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 <section id="module-email.policy">
<h1><a class="reference internal" href="#module-email.policy" title="email.policy: Controlling the parsing and generating of messages"><code class="xref py py-mod docutils literal notranslate">email.policy</code></a>: Policy Objects<a class="headerlink" href="#module-email.policy" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
New in version 3.3.
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Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/email/policy.py">Lib/email/policy.py</a>
<hr class="docutils" />
The <a class="reference internal" href="email.html#module-email" title="email: Package supporting the parsing, manipulating, and generating email messages."><code class="xref py py-mod docutils literal notranslate">email</code></a> package’s prime focus is the handling of email messages as
described by the various email and MIME RFCs. However, the general format of
email messages (a block of header fields each consisting of a name followed by
a colon followed by a value, the whole block followed by a blank line and an
arbitrary ‘body’), is a format that has found utility outside of the realm of
email. Some of these uses conform fairly closely to the main email RFCs, some
do not. Even when working with email, there are times when it is desirable to
break strict compliance with the RFCs, such as generating emails that
interoperate with email servers that do not themselves follow the standards, or
that implement extensions you want to use in ways that violate the
standards.
Policy objects give the email package the flexibility to handle all these
disparate use cases.
A <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> object encapsulates a set of attributes and methods that
control the behavior of various components of the email package during use.
<a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> instances can be passed to various classes and methods in the
email package to alter the default behavior. The settable values and their
defaults are described below.
There is a default policy used by all classes in the email package. For all of
the <a class="reference internal" href="email.parser.html#module-email.parser" title="email.parser: Parse flat text email messages to produce a message object structure."><code class="xref py py-mod docutils literal notranslate">parser</code></a> classes and the related convenience functions, and for
the <a class="reference internal" href="email.compat32-message.html#email.message.Message" title="email.message.Message"><code class="xref py py-class docutils literal notranslate">Message</code></a> class, this is the <a class="reference internal" href="#email.policy.Compat32" title="email.policy.Compat32"><code class="xref py py-class docutils literal notranslate">Compat32</code></a>
policy, via its corresponding pre-defined instance <a class="reference internal" href="#email.policy.compat32" title="email.policy.compat32"><code class="xref py py-const docutils literal notranslate">compat32</code></a>. This
policy provides for complete backward compatibility (in some cases, including
bug compatibility) with the pre-Python3.3 version of the email package.
This default value for the policy keyword to
<a class="reference internal" href="email.message.html#email.message.EmailMessage" title="email.message.EmailMessage"><code class="xref py py-class docutils literal notranslate">EmailMessage</code></a> is the <a class="reference internal" href="#email.policy.EmailPolicy" title="email.policy.EmailPolicy"><code class="xref py py-class docutils literal notranslate">EmailPolicy</code></a> policy, via
its pre-defined instance <a class="reference internal" href="#email.policy.default" title="email.policy.default"><code class="xref py py-data docutils literal notranslate">default</code></a>.
When a <a class="reference internal" href="email.compat32-message.html#email.message.Message" title="email.message.Message"><code class="xref py py-class docutils literal notranslate">Message</code></a> or <a class="reference internal" href="email.message.html#email.message.EmailMessage" title="email.message.EmailMessage"><code class="xref py py-class docutils literal notranslate">EmailMessage</code></a>
object is created, it acquires a policy. If the message is created by a
<a class="reference internal" href="email.parser.html#module-email.parser" title="email.parser: Parse flat text email messages to produce a message object structure."><code class="xref py py-mod docutils literal notranslate">parser</code></a>, a policy passed to the parser will be the policy used by
the message it creates. If the message is created by the program, then the
policy can be specified when it is created. When a message is passed to a
<a class="reference internal" href="email.generator.html#module-email.generator" title="email.generator: Generate flat text email messages from a message structure."><code class="xref py py-mod docutils literal notranslate">generator</code></a>, the generator uses the policy from the message by
default, but you can also pass a specific policy to the generator that will
override the one stored on the message object.
The default value for the policy keyword for the <a class="reference internal" href="email.parser.html#module-email.parser" title="email.parser: Parse flat text email messages to produce a message object structure."><code class="xref py py-mod docutils literal notranslate">email.parser</code></a> classes
and the parser convenience functions will be changing in a future version of
Python. Therefore you should always specify explicitly which policy you want
to use when calling any of the classes and functions described in the
<a class="reference internal" href="email.parser.html#module-email.parser" title="email.parser: Parse flat text email messages to produce a message object structure."><code class="xref py py-mod docutils literal notranslate">parser</code></a> module.
The first part of this documentation covers the features of <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a>, an
<a class="reference internal" href="../glossary.html#term-abstract-base-class">abstract base class</a> that defines the features that are common to all
policy objects, including <a class="reference internal" href="#email.policy.compat32" title="email.policy.compat32"><code class="xref py py-const docutils literal notranslate">compat32</code></a>. This includes certain hook
methods that are called internally by the email package, which a custom policy
could override to obtain different behavior. The second part describes the
concrete classes <a class="reference internal" href="#email.policy.EmailPolicy" title="email.policy.EmailPolicy"><code class="xref py py-class docutils literal notranslate">EmailPolicy</code></a> and <a class="reference internal" href="#email.policy.Compat32" title="email.policy.Compat32"><code class="xref py py-class docutils literal notranslate">Compat32</code></a>, which implement
the hooks that provide the standard behavior and the backward compatible
behavior and features, respectively.
<a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> instances are immutable, but they can be cloned, accepting the
same keyword arguments as the class constructor and returning a new
<a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> instance that is a copy of the original but with the specified
attributes values changed.
As an example, the following code could be used to read an email message from a
file on disk and pass it to the system <code class="docutils literal notranslate">sendmail</code> program on a Unix system:
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from email import message_from_binary_file
&gt;&gt;&gt; from email.generator import BytesGenerator
&gt;&gt;&gt; from email import policy
&gt;&gt;&gt; from subprocess import Popen, PIPE
&gt;&gt;&gt; with open(&#39;mymsg.txt&#39;, &#39;rb&#39;) as f:
... msg = message_from_binary_file(f, policy=policy.default)
&gt;&gt;&gt; p = Popen([&#39;sendmail&#39;, msg[&#39;To&#39;].addresses[0]], stdin=PIPE)
&gt;&gt;&gt; g = BytesGenerator(p.stdin, policy=msg.policy.clone(linesep=&#39;\r\n&#39;))
&gt;&gt;&gt; g.flatten(msg)
&gt;&gt;&gt; p.stdin.close()
&gt;&gt;&gt; rc = p.wait()
</pre></div>
</div>
Here we are telling <a class="reference internal" href="email.generator.html#email.generator.BytesGenerator" title="email.generator.BytesGenerator"><code class="xref py py-class docutils literal notranslate">BytesGenerator</code></a> to use the RFC
correct line separator characters when creating the binary string to feed into
<code class="docutils literal notranslate">sendmail's</code> <code class="docutils literal notranslate">stdin</code>, where the default policy would use <code class="docutils literal notranslate">\n</code> line
separators.
Some email package methods accept a policy keyword argument, allowing the
policy to be overridden for that method. For example, the following code uses
the <a class="reference internal" href="email.compat32-message.html#email.message.Message.as_bytes" title="email.message.Message.as_bytes"><code class="xref py py-meth docutils literal notranslate">as_bytes()</code></a> method of the msg object from
the previous example and writes the message to a file using the native line
separators for the platform on which it is running:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import os
&gt;&gt;&gt; with open(&#39;converted.txt&#39;, &#39;wb&#39;) as f:
... f.write(msg.as_bytes(policy=msg.policy.clone(linesep=os.linesep)))
17
</pre></div>
</div>
Policy objects can also be combined using the addition operator, producing a
policy object whose settings are a combination of the non-default values of the
summed objects:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; compat_SMTP = policy.compat32.clone(linesep=&#39;\r\n&#39;)
&gt;&gt;&gt; compat_strict = policy.compat32.clone(raise_on_defect=True)
&gt;&gt;&gt; compat_strict_SMTP = compat_SMTP + compat_strict
</pre></div>
</div>
This operation is not commutative; that is, the order in which the objects are
added matters. To illustrate:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; policy100 = policy.compat32.clone(max_line_length=100)
&gt;&gt;&gt; policy80 = policy.compat32.clone(max_line_length=80)
&gt;&gt;&gt; apolicy = policy100 + policy80
&gt;&gt;&gt; apolicy.max_line_length
80
&gt;&gt;&gt; apolicy = policy80 + policy100
&gt;&gt;&gt; apolicy.max_line_length
100
</pre></div>
</div>
<dl class="py class">
<dt class="sig sig-object py" id="email.policy.Policy">
class email.policy.Policy(**kw)<a class="headerlink" href="#email.policy.Policy" title="Permalink to this definition">¶</a></dt>
<dd>This is the <a class="reference internal" href="../glossary.html#term-abstract-base-class">abstract base class</a> for all policy classes. It provides
default implementations for a couple of trivial methods, as well as the
implementation of the immutability property, the <a class="reference internal" href="#email.policy.Policy.clone" title="email.policy.Policy.clone"><code class="xref py py-meth docutils literal notranslate">clone()</code></a> method, and
the constructor semantics.
The constructor of a policy class can be passed various keyword arguments.
The arguments that may be specified are any non-method properties on this
class, plus any additional non-method properties on the concrete class. A
value specified in the constructor will override the default value for the
corresponding attribute.
This class defines the following properties, and thus values for the
following may be passed in the constructor of any policy class:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.max_line_length">
max_line_length<a class="headerlink" href="#email.policy.Policy.max_line_length" title="Permalink to this definition">¶</a></dt>
<dd>The maximum length of any line in the serialized output, not counting the
end of line character(s). Default is 78, per <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>. A value of
<code class="docutils literal notranslate">0</code> or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate">None</code></a> indicates that no line wrapping should be
done at all.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.linesep">
linesep<a class="headerlink" href="#email.policy.Policy.linesep" title="Permalink to this definition">¶</a></dt>
<dd>The string to be used to terminate lines in serialized output. The
default is <code class="docutils literal notranslate">\n</code> because that’s the internal end-of-line discipline used
by Python, though <code class="docutils literal notranslate">\r\n</code> is required by the RFCs.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.cte_type">
cte_type<a class="headerlink" href="#email.policy.Policy.cte_type" title="Permalink to this definition">¶</a></dt>
<dd>Controls the type of Content Transfer Encodings that may be or are
required to be used. The possible values are:
<table class="docutils align-default">
<colgroup>
<col style="width: 11%" />
<col style="width: 89%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><code class="docutils literal notranslate">7bit</code></td>
<td>all data must be “7 bit clean” (ASCII-only). This means that
where necessary data will be encoded using either
quoted-printable or base64 encoding.</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">8bit</code></td>
<td>data is not constrained to be 7 bit clean. Data in headers is
still required to be ASCII-only and so will be encoded (see
<a class="reference internal" href="#email.policy.Policy.fold_binary" title="email.policy.Policy.fold_binary"><code class="xref py py-meth docutils literal notranslate">fold_binary()</code></a> and <a class="reference internal" href="#email.policy.EmailPolicy.utf8" title="email.policy.EmailPolicy.utf8"><code class="xref py py-attr docutils literal notranslate">utf8</code></a> below for
exceptions), but body parts may use the <code class="docutils literal notranslate">8bit</code> CTE.</td>
</tr>
</tbody>
</table>
A <code class="docutils literal notranslate">cte_type</code> value of <code class="docutils literal notranslate">8bit</code> only works with <code class="docutils literal notranslate">BytesGenerator</code>, not
<code class="docutils literal notranslate">Generator</code>, because strings cannot contain binary data. If a
<code class="docutils literal notranslate">Generator</code> is operating under a policy that specifies
<code class="docutils literal notranslate">cte_type=8bit</code>, it will act as if <code class="docutils literal notranslate">cte_type</code> is <code class="docutils literal notranslate">7bit</code>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.raise_on_defect">
raise_on_defect<a class="headerlink" href="#email.policy.Policy.raise_on_defect" title="Permalink to this definition">¶</a></dt>
<dd>If <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>, any defects encountered will be raised as errors. If
<a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a> (the default), defects will be passed to the
<a class="reference internal" href="#email.policy.Policy.register_defect" title="email.policy.Policy.register_defect"><code class="xref py py-meth docutils literal notranslate">register_defect()</code></a> method.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.mangle_from_">
mangle_from_<a class="headerlink" href="#email.policy.Policy.mangle_from_" title="Permalink to this definition">¶</a></dt>
<dd>If <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>, lines starting with “From “ in the body are
escaped by putting a <code class="docutils literal notranslate">&gt;</code> in front of them. This parameter is used when
the message is being serialized by a generator.
Default: <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a>.
<div class="versionadded">
New in version 3.5: The mangle_from_ parameter.
</div>
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.message_factory">
message_factory<a class="headerlink" href="#email.policy.Policy.message_factory" title="Permalink to this definition">¶</a></dt>
<dd>A factory function for constructing a new empty message object. Used
by the parser when building messages. Defaults to <code class="docutils literal notranslate">None</code>, in
which case <a class="reference internal" href="email.compat32-message.html#email.message.Message" title="email.message.Message"><code class="xref py py-class docutils literal notranslate">Message</code></a> is used.
<div class="versionadded">
New in version 3.6.
</div>
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Policy.verify_generated_headers">
verify_generated_headers<a class="headerlink" href="#email.policy.Policy.verify_generated_headers" title="Permalink to this definition">¶</a></dt>
<dd>If <code class="docutils literal notranslate">True</code> (the default), the generator will raise
<a class="reference internal" href="email.errors.html#email.errors.HeaderWriteError" title="email.errors.HeaderWriteError"><code class="xref py py-exc docutils literal notranslate">HeaderWriteError</code></a> instead of writing a header
that is improperly folded or delimited, such that it would
be parsed as multiple headers or joined with adjacent data.
Such headers can be generated by custom header classes or bugs
in the <code class="docutils literal notranslate">email</code> module.
As it’s a security feature, this defaults to <code class="docutils literal notranslate">True</code> even in the
<a class="reference internal" href="#email.policy.Compat32" title="email.policy.Compat32"><code class="xref py py-class docutils literal notranslate">Compat32</code></a> policy.
For backwards compatible, but unsafe, behavior, it must be set to
<code class="docutils literal notranslate">False</code> explicitly.
<div class="versionadded">
New in version 3.10.15.
</div>
</dd></dl>

The following <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> method is intended to be called by code using
the email library to create policy instances with custom settings:
<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.clone">
clone(**kw)<a class="headerlink" href="#email.policy.Policy.clone" title="Permalink to this definition">¶</a></dt>
<dd>Return a new <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> instance whose attributes have the same
values as the current instance, except where those attributes are
given new values by the keyword arguments.
</dd></dl>

The remaining <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> methods are called by the email package code,
and are not intended to be called by an application using the email package.
A custom policy must implement all of these methods.
<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.handle_defect">
handle_defect(obj, defect)<a class="headerlink" href="#email.policy.Policy.handle_defect" title="Permalink to this definition">¶</a></dt>
<dd>Handle a defect found on obj. When the email package calls this
method, defect will always be a subclass of
<code class="xref py py-class docutils literal notranslate">Defect</code>.
The default implementation checks the <a class="reference internal" href="#email.policy.Policy.raise_on_defect" title="email.policy.Policy.raise_on_defect"><code class="xref py py-attr docutils literal notranslate">raise_on_defect</code></a> flag. If
it is <code class="docutils literal notranslate">True</code>, defect is raised as an exception. If it is <code class="docutils literal notranslate">False</code>
(the default), obj and defect are passed to <a class="reference internal" href="#email.policy.Policy.register_defect" title="email.policy.Policy.register_defect"><code class="xref py py-meth docutils literal notranslate">register_defect()</code></a>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.register_defect">
register_defect(obj, defect)<a class="headerlink" href="#email.policy.Policy.register_defect" title="Permalink to this definition">¶</a></dt>
<dd>Register a defect on obj. In the email package, defect will always
be a subclass of <code class="xref py py-class docutils literal notranslate">Defect</code>.
The default implementation calls the <code class="docutils literal notranslate">append</code> method of the <code class="docutils literal notranslate">defects</code>
attribute of obj. When the email package calls <a class="reference internal" href="#email.policy.Policy.handle_defect" title="email.policy.Policy.handle_defect"><code class="xref py py-attr docutils literal notranslate">handle_defect</code></a>,
obj will normally have a <code class="docutils literal notranslate">defects</code> attribute that has an <code class="docutils literal notranslate">append</code>
method. Custom object types used with the email package (for example,
custom <code class="docutils literal notranslate">Message</code> objects) should also provide such an attribute,
otherwise defects in parsed messages will raise unexpected errors.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.header_max_count">
header_max_count(name)<a class="headerlink" href="#email.policy.Policy.header_max_count" title="Permalink to this definition">¶</a></dt>
<dd>Return the maximum allowed number of headers named name.
Called when a header is added to an <a class="reference internal" href="email.message.html#email.message.EmailMessage" title="email.message.EmailMessage"><code class="xref py py-class docutils literal notranslate">EmailMessage</code></a>
or <a class="reference internal" href="email.compat32-message.html#email.message.Message" title="email.message.Message"><code class="xref py py-class docutils literal notranslate">Message</code></a> object. If the returned value is not
<code class="docutils literal notranslate">0</code> or <code class="docutils literal notranslate">None</code>, and there are already a number of headers with the
name name greater than or equal to the value returned, a
<a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a> is raised.
Because the default behavior of <code class="docutils literal notranslate">Message.__setitem__</code> is to append the
value to the list of headers, it is easy to create duplicate headers
without realizing it. This method allows certain headers to be limited
in the number of instances of that header that may be added to a
<code class="docutils literal notranslate">Message</code> programmatically. (The limit is not observed by the parser,
which will faithfully produce as many headers as exist in the message
being parsed.)
The default implementation returns <code class="docutils literal notranslate">None</code> for all header names.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.header_source_parse">
header_source_parse(sourcelines)<a class="headerlink" href="#email.policy.Policy.header_source_parse" title="Permalink to this definition">¶</a></dt>
<dd>The email package calls this method with a list of strings, each string
ending with the line separation characters found in the source being
parsed. The first line includes the field header name and separator.
All whitespace in the source is preserved. The method should return the
<code class="docutils literal notranslate">(name, value)</code> tuple that is to be stored in the <code class="docutils literal notranslate">Message</code> to
represent the parsed header.
If an implementation wishes to retain compatibility with the existing
email package policies, name should be the case preserved name (all
characters up to the ‘<code class="docutils literal notranslate">:</code>’ separator), while value should be the
unfolded value (all line separator characters removed, but whitespace
kept intact), stripped of leading whitespace.
sourcelines may contain surrogateescaped binary data.
There is no default implementation
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.header_store_parse">
header_store_parse(name, value)<a class="headerlink" href="#email.policy.Policy.header_store_parse" title="Permalink to this definition">¶</a></dt>
<dd>The email package calls this method with the name and value provided by
the application program when the application program is modifying a
<code class="docutils literal notranslate">Message</code> programmatically (as opposed to a <code class="docutils literal notranslate">Message</code> created by a
parser). The method should return the <code class="docutils literal notranslate">(name, value)</code> tuple that is to
be stored in the <code class="docutils literal notranslate">Message</code> to represent the header.
If an implementation wishes to retain compatibility with the existing
email package policies, the name and value should be strings or
string subclasses that do not change the content of the passed in
arguments.
There is no default implementation
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.header_fetch_parse">
header_fetch_parse(name, value)<a class="headerlink" href="#email.policy.Policy.header_fetch_parse" title="Permalink to this definition">¶</a></dt>
<dd>The email package calls this method with the name and value currently
stored in the <code class="docutils literal notranslate">Message</code> when that header is requested by the
application program, and whatever the method returns is what is passed
back to the application as the value of the header being retrieved.
Note that there may be more than one header with the same name stored in
the <code class="docutils literal notranslate">Message</code>; the method is passed the specific name and value of the
header destined to be returned to the application.
value may contain surrogateescaped binary data. There should be no
surrogateescaped binary data in the value returned by the method.
There is no default implementation
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.fold">
fold(name, value)<a class="headerlink" href="#email.policy.Policy.fold" title="Permalink to this definition">¶</a></dt>
<dd>The email package calls this method with the name and value currently
stored in the <code class="docutils literal notranslate">Message</code> for a given header. The method should return a
string that represents that header “folded” correctly (according to the
policy settings) by composing the name with the value and inserting
<a class="reference internal" href="#email.policy.Policy.linesep" title="email.policy.Policy.linesep"><code class="xref py py-attr docutils literal notranslate">linesep</code></a> characters at the appropriate places. See <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>
for a discussion of the rules for folding email headers.
value may contain surrogateescaped binary data. There should be no
surrogateescaped binary data in the string returned by the method.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Policy.fold_binary">
fold_binary(name, value)<a class="headerlink" href="#email.policy.Policy.fold_binary" title="Permalink to this definition">¶</a></dt>
<dd>The same as <a class="reference internal" href="#email.policy.Policy.fold" title="email.policy.Policy.fold"><code class="xref py py-meth docutils literal notranslate">fold()</code></a>, except that the returned value should be a
bytes object rather than a string.
value may contain surrogateescaped binary data. These could be
converted back into binary data in the returned bytes object.
</dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.policy.EmailPolicy">
class email.policy.EmailPolicy(**kw)<a class="headerlink" href="#email.policy.EmailPolicy" title="Permalink to this definition">¶</a></dt>
<dd>This concrete <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> provides behavior that is intended to be fully
compliant with the current email RFCs. These include (but are not limited
to) <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>, <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2047.html">RFC 2047</a>, and the current MIME RFCs.
This policy adds new header parsing and folding algorithms. Instead of
simple strings, headers are <code class="docutils literal notranslate">str</code> subclasses with attributes that depend
on the type of the field. The parsing and folding algorithm fully implement
<a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2047.html">RFC 2047</a> and <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>.
The default value for the <a class="reference internal" href="#email.policy.Policy.message_factory" title="email.policy.Policy.message_factory"><code class="xref py py-attr docutils literal notranslate">message_factory</code></a>
attribute is <a class="reference internal" href="email.message.html#email.message.EmailMessage" title="email.message.EmailMessage"><code class="xref py py-class docutils literal notranslate">EmailMessage</code></a>.
In addition to the settable attributes listed above that apply to all
policies, this policy adds the following additional attributes:
<div class="versionadded">
New in version 3.6: <a class="footnote-reference brackets" href="#id2" id="id1">1</a>
</div>
<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.utf8">
utf8<a class="headerlink" href="#email.policy.EmailPolicy.utf8" title="Permalink to this definition">¶</a></dt>
<dd>If <code class="docutils literal notranslate">False</code>, follow <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>, supporting non-ASCII characters in
headers by encoding them as “encoded words”. If <code class="docutils literal notranslate">True</code>, follow
<a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc6532.html">RFC 6532</a> and use <code class="docutils literal notranslate">utf-8</code> encoding for headers. Messages
formatted in this way may be passed to SMTP servers that support
the <code class="docutils literal notranslate">SMTPUTF8</code> extension (<a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc6531.html">RFC 6531</a>).
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.refold_source">
refold_source<a class="headerlink" href="#email.policy.EmailPolicy.refold_source" title="Permalink to this definition">¶</a></dt>
<dd>If the value for a header in the <code class="docutils literal notranslate">Message</code> object originated from a
<a class="reference internal" href="email.parser.html#module-email.parser" title="email.parser: Parse flat text email messages to produce a message object structure."><code class="xref py py-mod docutils literal notranslate">parser</code></a> (as opposed to being set by a program), this
attribute indicates whether or not a generator should refold that value
when transforming the message back into serialized form. The possible
values are:
<table class="docutils align-default">
<colgroup>
<col style="width: 11%" />
<col style="width: 89%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><code class="docutils literal notranslate">none</code></td>
<td>all source values use original folding</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate">long</code></td>
<td>source values that have any line that is longer than
<code class="docutils literal notranslate">max_line_length</code> will be refolded</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate">all</code></td>
<td>all values are refolded.</td>
</tr>
</tbody>
</table>
The default is <code class="docutils literal notranslate">long</code>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.header_factory">
header_factory<a class="headerlink" href="#email.policy.EmailPolicy.header_factory" title="Permalink to this definition">¶</a></dt>
<dd>A callable that takes two arguments, <code class="docutils literal notranslate">name</code> and <code class="docutils literal notranslate">value</code>, where
<code class="docutils literal notranslate">name</code> is a header field name and <code class="docutils literal notranslate">value</code> is an unfolded header field
value, and returns a string subclass that represents that header. A
default <code class="docutils literal notranslate">header_factory</code> (see <a class="reference internal" href="email.headerregistry.html#module-email.headerregistry" title="email.headerregistry: Automatic Parsing of headers based on the field name"><code class="xref py py-mod docutils literal notranslate">headerregistry</code></a>) is provided
that supports custom parsing for the various address and date <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>
header field types, and the major MIME header field stypes. Support for
additional custom parsing will be added in the future.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.content_manager">
content_manager<a class="headerlink" href="#email.policy.EmailPolicy.content_manager" title="Permalink to this definition">¶</a></dt>
<dd>An object with at least two methods: get_content and set_content. When
the <a class="reference internal" href="email.message.html#email.message.EmailMessage.get_content" title="email.message.EmailMessage.get_content"><code class="xref py py-meth docutils literal notranslate">get_content()</code></a> or
<a class="reference internal" href="email.message.html#email.message.EmailMessage.set_content" title="email.message.EmailMessage.set_content"><code class="xref py py-meth docutils literal notranslate">set_content()</code></a> method of an
<a class="reference internal" href="email.message.html#email.message.EmailMessage" title="email.message.EmailMessage"><code class="xref py py-class docutils literal notranslate">EmailMessage</code></a> object is called, it calls the
corresponding method of this object, passing it the message object as its
first argument, and any arguments or keywords that were passed to it as
additional arguments. By default <code class="docutils literal notranslate">content_manager</code> is set to
<a class="reference internal" href="email.contentmanager.html#email.contentmanager.raw_data_manager" title="email.contentmanager.raw_data_manager"><code class="xref py py-data docutils literal notranslate">raw_data_manager</code></a>.
<div class="versionadded">
New in version 3.4.
</div>
</dd></dl>

The class provides the following concrete implementations of the abstract
methods of <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a>:
<dl class="py method">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.header_max_count">
header_max_count(name)<a class="headerlink" href="#email.policy.EmailPolicy.header_max_count" title="Permalink to this definition">¶</a></dt>
<dd>Returns the value of the
<a class="reference internal" href="email.headerregistry.html#email.headerregistry.BaseHeader.max_count" title="email.headerregistry.BaseHeader.max_count"><code class="xref py py-attr docutils literal notranslate">max_count</code></a> attribute of the
specialized class used to represent the header with the given name.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.header_source_parse">
header_source_parse(sourcelines)<a class="headerlink" href="#email.policy.EmailPolicy.header_source_parse" title="Permalink to this definition">¶</a></dt>
<dd>The name is parsed as everything up to the ‘<code class="docutils literal notranslate">:</code>’ and returned
unmodified. The value is determined by stripping leading whitespace off
the remainder of the first line, joining all subsequent lines together,
and stripping any trailing carriage return or linefeed characters.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.header_store_parse">
header_store_parse(name, value)<a class="headerlink" href="#email.policy.EmailPolicy.header_store_parse" title="Permalink to this definition">¶</a></dt>
<dd>The name is returned unchanged. If the input value has a <code class="docutils literal notranslate">name</code>
attribute and it matches name ignoring case, the value is returned
unchanged. Otherwise the name and value are passed to
<code class="docutils literal notranslate">header_factory</code>, and the resulting header object is returned as
the value. In this case a <code class="docutils literal notranslate">ValueError</code> is raised if the input value
contains CR or LF characters.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.header_fetch_parse">
header_fetch_parse(name, value)<a class="headerlink" href="#email.policy.EmailPolicy.header_fetch_parse" title="Permalink to this definition">¶</a></dt>
<dd>If the value has a <code class="docutils literal notranslate">name</code> attribute, it is returned to unmodified.
Otherwise the name, and the value with any CR or LF characters
removed, are passed to the <code class="docutils literal notranslate">header_factory</code>, and the resulting
header object is returned. Any surrogateescaped bytes get turned into
the unicode unknown-character glyph.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.fold">
fold(name, value)<a class="headerlink" href="#email.policy.EmailPolicy.fold" title="Permalink to this definition">¶</a></dt>
<dd>Header folding is controlled by the <a class="reference internal" href="#email.policy.EmailPolicy.refold_source" title="email.policy.EmailPolicy.refold_source"><code class="xref py py-attr docutils literal notranslate">refold_source</code></a> policy setting.
A value is considered to be a ‘source value’ if and only if it does not
have a <code class="docutils literal notranslate">name</code> attribute (having a <code class="docutils literal notranslate">name</code> attribute means it is a
header object of some sort). If a source value needs to be refolded
according to the policy, it is converted into a header object by
passing the name and the value with any CR and LF characters removed
to the <code class="docutils literal notranslate">header_factory</code>. Folding of a header object is done by
calling its <code class="docutils literal notranslate">fold</code> method with the current policy.
Source values are split into lines using <a class="reference internal" href="stdtypes.html#str.splitlines" title="str.splitlines"><code class="xref py py-meth docutils literal notranslate">splitlines()</code></a>. If
the value is not to be refolded, the lines are rejoined using the
<code class="docutils literal notranslate">linesep</code> from the policy and returned. The exception is lines
containing non-ascii binary data. In that case the value is refolded
regardless of the <code class="docutils literal notranslate">refold_source</code> setting, which causes the binary data
to be CTE encoded using the <code class="docutils literal notranslate">unknown-8bit</code> charset.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.EmailPolicy.fold_binary">
fold_binary(name, value)<a class="headerlink" href="#email.policy.EmailPolicy.fold_binary" title="Permalink to this definition">¶</a></dt>
<dd>The same as <a class="reference internal" href="#email.policy.EmailPolicy.fold" title="email.policy.EmailPolicy.fold"><code class="xref py py-meth docutils literal notranslate">fold()</code></a> if <a class="reference internal" href="#email.policy.Policy.cte_type" title="email.policy.Policy.cte_type"><code class="xref py py-attr docutils literal notranslate">cte_type</code></a> is <code class="docutils literal notranslate">7bit</code>, except
that the returned value is bytes.
If <a class="reference internal" href="#email.policy.Policy.cte_type" title="email.policy.Policy.cte_type"><code class="xref py py-attr docutils literal notranslate">cte_type</code></a> is <code class="docutils literal notranslate">8bit</code>, non-ASCII binary data is
converted back
into bytes. Headers with binary data are not refolded, regardless of the
<code class="docutils literal notranslate">refold_header</code> setting, since there is no way to know whether the
binary data consists of single byte characters or multibyte characters.
</dd></dl>

</dd></dl>

The following instances of <a class="reference internal" href="#email.policy.EmailPolicy" title="email.policy.EmailPolicy"><code class="xref py py-class docutils literal notranslate">EmailPolicy</code></a> provide defaults suitable for
specific application domains. Note that in the future the behavior of these
instances (in particular the <code class="docutils literal notranslate">HTTP</code> instance) may be adjusted to conform even
more closely to the RFCs relevant to their domains.
<dl class="py data">
<dt class="sig sig-object py" id="email.policy.default">
email.policy.default<a class="headerlink" href="#email.policy.default" title="Permalink to this definition">¶</a></dt>
<dd>An instance of <code class="docutils literal notranslate">EmailPolicy</code> with all defaults unchanged. This policy
uses the standard Python <code class="docutils literal notranslate">\n</code> line endings rather than the RFC-correct
<code class="docutils literal notranslate">\r\n</code>.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="email.policy.SMTP">
email.policy.SMTP<a class="headerlink" href="#email.policy.SMTP" title="Permalink to this definition">¶</a></dt>
<dd>Suitable for serializing messages in conformance with the email RFCs.
Like <code class="docutils literal notranslate">default</code>, but with <code class="docutils literal notranslate">linesep</code> set to <code class="docutils literal notranslate">\r\n</code>, which is RFC
compliant.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="email.policy.SMTPUTF8">
email.policy.SMTPUTF8<a class="headerlink" href="#email.policy.SMTPUTF8" title="Permalink to this definition">¶</a></dt>
<dd>The same as <code class="docutils literal notranslate">SMTP</code> except that <a class="reference internal" href="#email.policy.EmailPolicy.utf8" title="email.policy.EmailPolicy.utf8"><code class="xref py py-attr docutils literal notranslate">utf8</code></a> is <code class="docutils literal notranslate">True</code>.
Useful for serializing messages to a message store without using encoded
words in the headers. Should only be used for SMTP transmission if the
sender or recipient addresses have non-ASCII characters (the
<a class="reference internal" href="smtplib.html#smtplib.SMTP.send_message" title="smtplib.SMTP.send_message"><code class="xref py py-meth docutils literal notranslate">smtplib.SMTP.send_message()</code></a> method handles this automatically).
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="email.policy.HTTP">
email.policy.HTTP<a class="headerlink" href="#email.policy.HTTP" title="Permalink to this definition">¶</a></dt>
<dd>Suitable for serializing headers with for use in HTTP traffic. Like
<code class="docutils literal notranslate">SMTP</code> except that <code class="docutils literal notranslate">max_line_length</code> is set to <code class="docutils literal notranslate">None</code> (unlimited).
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="email.policy.strict">
email.policy.strict<a class="headerlink" href="#email.policy.strict" title="Permalink to this definition">¶</a></dt>
<dd>Convenience instance. The same as <code class="docutils literal notranslate">default</code> except that
<code class="docutils literal notranslate">raise_on_defect</code> is set to <code class="docutils literal notranslate">True</code>. This allows any policy to be made
strict by writing:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>somepolicy + policy.strict
</pre></div>
</div>
</dd></dl>

With all of these <a class="reference internal" href="#email.policy.EmailPolicy" title="email.policy.EmailPolicy"><code class="xref py py-class docutils literal notranslate">EmailPolicies</code></a>, the effective API of
the email package is changed from the Python 3.2 API in the following ways:
<blockquote>
<div><ul class="simple">
<li>Setting a header on a <a class="reference internal" href="email.compat32-message.html#email.message.Message" title="email.message.Message"><code class="xref py py-class docutils literal notranslate">Message</code></a> results in that
header being parsed and a header object created.</li>
<li>Fetching a header value from a <a class="reference internal" href="email.compat32-message.html#email.message.Message" title="email.message.Message"><code class="xref py py-class docutils literal notranslate">Message</code></a> results
in that header being parsed and a header object created and
returned.</li>
<li>Any header object, or any header that is refolded due to the
policy settings, is folded using an algorithm that fully implements the
RFC folding algorithms, including knowing where encoded words are required
and allowed.</li>
</ul>
</div></blockquote>
From the application view, this means that any header obtained through the
<a class="reference internal" href="email.message.html#email.message.EmailMessage" title="email.message.EmailMessage"><code class="xref py py-class docutils literal notranslate">EmailMessage</code></a> is a header object with extra
attributes, whose string value is the fully decoded unicode value of the
header. Likewise, a header may be assigned a new value, or a new header
created, using a unicode string, and the policy will take care of converting
the unicode string into the correct RFC encoded form.
The header objects and their attributes are described in
<a class="reference internal" href="email.headerregistry.html#module-email.headerregistry" title="email.headerregistry: Automatic Parsing of headers based on the field name"><code class="xref py py-mod docutils literal notranslate">headerregistry</code></a>.
<dl class="py class">
<dt class="sig sig-object py" id="email.policy.Compat32">
class email.policy.Compat32(**kw)<a class="headerlink" href="#email.policy.Compat32" title="Permalink to this definition">¶</a></dt>
<dd>This concrete <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> is the backward compatibility policy. It
replicates the behavior of the email package in Python 3.2. The
<a class="reference internal" href="#module-email.policy" title="email.policy: Controlling the parsing and generating of messages"><code class="xref py py-mod docutils literal notranslate">policy</code></a> module also defines an instance of this class,
<a class="reference internal" href="#email.policy.compat32" title="email.policy.compat32"><code class="xref py py-const docutils literal notranslate">compat32</code></a>, that is used as the default policy. Thus the default
behavior of the email package is to maintain compatibility with Python 3.2.
The following attributes have values that are different from the
<a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a> default:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.policy.Compat32.mangle_from_">
mangle_from_<a class="headerlink" href="#email.policy.Compat32.mangle_from_" title="Permalink to this definition">¶</a></dt>
<dd>The default is <code class="docutils literal notranslate">True</code>.
</dd></dl>

The class provides the following concrete implementations of the
abstract methods of <a class="reference internal" href="#email.policy.Policy" title="email.policy.Policy"><code class="xref py py-class docutils literal notranslate">Policy</code></a>:
<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Compat32.header_source_parse">
header_source_parse(sourcelines)<a class="headerlink" href="#email.policy.Compat32.header_source_parse" title="Permalink to this definition">¶</a></dt>
<dd>The name is parsed as everything up to the ‘<code class="docutils literal notranslate">:</code>’ and returned
unmodified. The value is determined by stripping leading whitespace off
the remainder of the first line, joining all subsequent lines together,
and stripping any trailing carriage return or linefeed characters.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Compat32.header_store_parse">
header_store_parse(name, value)<a class="headerlink" href="#email.policy.Compat32.header_store_parse" title="Permalink to this definition">¶</a></dt>
<dd>The name and value are returned unmodified.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Compat32.header_fetch_parse">
header_fetch_parse(name, value)<a class="headerlink" href="#email.policy.Compat32.header_fetch_parse" title="Permalink to this definition">¶</a></dt>
<dd>If the value contains binary data, it is converted into a
<a class="reference internal" href="email.header.html#email.header.Header" title="email.header.Header"><code class="xref py py-class docutils literal notranslate">Header</code></a> object using the <code class="docutils literal notranslate">unknown-8bit</code> charset.
Otherwise it is returned unmodified.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Compat32.fold">
fold(name, value)<a class="headerlink" href="#email.policy.Compat32.fold" title="Permalink to this definition">¶</a></dt>
<dd>Headers are folded using the <a class="reference internal" href="email.header.html#email.header.Header" title="email.header.Header"><code class="xref py py-class docutils literal notranslate">Header</code></a> folding
algorithm, which preserves existing line breaks in the value, and wraps
each resulting line to the <code class="docutils literal notranslate">max_line_length</code>. Non-ASCII binary data are
CTE encoded using the <code class="docutils literal notranslate">unknown-8bit</code> charset.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.policy.Compat32.fold_binary">
fold_binary(name, value)<a class="headerlink" href="#email.policy.Compat32.fold_binary" title="Permalink to this definition">¶</a></dt>
<dd>Headers are folded using the <a class="reference internal" href="email.header.html#email.header.Header" title="email.header.Header"><code class="xref py py-class docutils literal notranslate">Header</code></a> folding
algorithm, which preserves existing line breaks in the value, and wraps
each resulting line to the <code class="docutils literal notranslate">max_line_length</code>. If <code class="docutils literal notranslate">cte_type</code> is
<code class="docutils literal notranslate">7bit</code>, non-ascii binary data is CTE encoded using the <code class="docutils literal notranslate">unknown-8bit</code>
charset. Otherwise the original source header is used, with its existing
line breaks and any (RFC invalid) binary data it may contain.
</dd></dl>

</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="email.policy.compat32">
email.policy.compat32<a class="headerlink" href="#email.policy.compat32" title="Permalink to this definition">¶</a></dt>
<dd>An instance of <a class="reference internal" href="#email.policy.Compat32" title="email.policy.Compat32"><code class="xref py py-class docutils literal notranslate">Compat32</code></a>, providing backward compatibility with the
behavior of the email package in Python 3.2.
</dd></dl>

Footnotes
<dl class="footnote brackets">
<dt class="label" id="id2"><a class="fn-backref" href="#id1">1</a></dt>
<dd>Originally added in 3.3 as a <a class="reference internal" href="../glossary.html#term-provisional-package">provisional feature</a>.
</dd>
</dl>
</section>

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