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 <section id="module-email.headerregistry">
<h1><a class="reference internal" href="#module-email.headerregistry" title="email.headerregistry: Automatic Parsing of headers based on the field name"><code class="xref py py-mod docutils literal notranslate">email.headerregistry</code></a>: Custom Header Objects<a class="headerlink" href="#module-email.headerregistry" title="Permalink to this headline">¶</a></h1>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.10/Lib/email/headerregistry.py">Lib/email/headerregistry.py</a>
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New in version 3.6: <a class="footnote-reference brackets" href="#id2" id="id1">1</a>
</div>
Headers are represented by customized subclasses of <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>. The
particular class used to represent a given header is determined by the
<a class="reference internal" href="email.policy.html#email.policy.EmailPolicy.header_factory" title="email.policy.EmailPolicy.header_factory"><code class="xref py py-attr docutils literal notranslate">header_factory</code></a> of the <a class="reference internal" href="email.policy.html#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> in
effect when the headers are created. This section documents the particular
<code class="docutils literal notranslate">header_factory</code> implemented by the email package for handling <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>
compliant email messages, which not only provides customized header objects for
various header types, but also provides an extension mechanism for applications
to add their own custom header types.
When using any of the policy objects derived from
<a class="reference internal" href="email.policy.html#email.policy.EmailPolicy" title="email.policy.EmailPolicy"><code class="xref py py-data docutils literal notranslate">EmailPolicy</code></a>, all headers are produced by
<a class="reference internal" href="#email.headerregistry.HeaderRegistry" title="email.headerregistry.HeaderRegistry"><code class="xref py py-class docutils literal notranslate">HeaderRegistry</code></a> and have <a class="reference internal" href="#email.headerregistry.BaseHeader" title="email.headerregistry.BaseHeader"><code class="xref py py-class docutils literal notranslate">BaseHeader</code></a> as their last base
class. Each header class has an additional base class that is determined by
the type of the header. For example, many headers have the class
<a class="reference internal" href="#email.headerregistry.UnstructuredHeader" title="email.headerregistry.UnstructuredHeader"><code class="xref py py-class docutils literal notranslate">UnstructuredHeader</code></a> as their other base class. The specialized second
class for a header is determined by the name of the header, using a lookup
table stored in the <a class="reference internal" href="#email.headerregistry.HeaderRegistry" title="email.headerregistry.HeaderRegistry"><code class="xref py py-class docutils literal notranslate">HeaderRegistry</code></a>. All of this is managed
transparently for the typical application program, but interfaces are provided
for modifying the default behavior for use by more complex applications.
The sections below first document the header base classes and their attributes,
followed by the API for modifying the behavior of <a class="reference internal" href="#email.headerregistry.HeaderRegistry" title="email.headerregistry.HeaderRegistry"><code class="xref py py-class docutils literal notranslate">HeaderRegistry</code></a>, and
finally the support classes used to represent the data parsed from structured
headers.
<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.BaseHeader">
class email.headerregistry.BaseHeader(name, value)<a class="headerlink" href="#email.headerregistry.BaseHeader" title="Permalink to this definition">¶</a></dt>
<dd>name and value are passed to <code class="docutils literal notranslate">BaseHeader</code> from the
<a class="reference internal" href="email.policy.html#email.policy.EmailPolicy.header_factory" title="email.policy.EmailPolicy.header_factory"><code class="xref py py-attr docutils literal notranslate">header_factory</code></a> call. The string value of
any header object is the value fully decoded to unicode.
This base class defines the following read-only properties:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.BaseHeader.name">
name<a class="headerlink" href="#email.headerregistry.BaseHeader.name" title="Permalink to this definition">¶</a></dt>
<dd>The name of the header (the portion of the field before the ‘:’). This
is exactly the value passed in the
<a class="reference internal" href="email.policy.html#email.policy.EmailPolicy.header_factory" title="email.policy.EmailPolicy.header_factory"><code class="xref py py-attr docutils literal notranslate">header_factory</code></a> call for name; that
is, case is preserved.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.BaseHeader.defects">
defects<a class="headerlink" href="#email.headerregistry.BaseHeader.defects" title="Permalink to this definition">¶</a></dt>
<dd>A tuple of <code class="xref py py-exc docutils literal notranslate">HeaderDefect</code> instances reporting any
RFC compliance problems found during parsing. The email package tries to
be complete about detecting compliance issues. See the <a class="reference internal" href="email.errors.html#module-email.errors" title="email.errors: The exception classes used by the email package."><code class="xref py py-mod docutils literal notranslate">errors</code></a>
module for a discussion of the types of defects that may be reported.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.BaseHeader.max_count">
max_count<a class="headerlink" href="#email.headerregistry.BaseHeader.max_count" title="Permalink to this definition">¶</a></dt>
<dd>The maximum number of headers of this type that can have the same
<code class="docutils literal notranslate">name</code>. A value of <code class="docutils literal notranslate">None</code> means unlimited. The <code class="docutils literal notranslate">BaseHeader</code> value
for this attribute is <code class="docutils literal notranslate">None</code>; it is expected that specialized header
classes will override this value as needed.
</dd></dl>

<code class="docutils literal notranslate">BaseHeader</code> also provides the following method, which is called by the
email library code and should not in general be called by application
programs:
<dl class="py method">
<dt class="sig sig-object py" id="email.headerregistry.BaseHeader.fold">
fold(*, policy)<a class="headerlink" href="#email.headerregistry.BaseHeader.fold" title="Permalink to this definition">¶</a></dt>
<dd>Return a string containing <a class="reference internal" href="email.policy.html#email.policy.Policy.linesep" title="email.policy.Policy.linesep"><code class="xref py py-attr docutils literal notranslate">linesep</code></a>
characters as required to correctly fold the header according to
policy. A <a class="reference internal" href="email.policy.html#email.policy.Policy.cte_type" title="email.policy.Policy.cte_type"><code class="xref py py-attr docutils literal notranslate">cte_type</code></a> of <code class="docutils literal notranslate">8bit</code> will be
treated as if it were <code class="docutils literal notranslate">7bit</code>, since headers may not contain arbitrary
binary data. If <a class="reference internal" href="email.policy.html#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">False</code>,
non-ASCII data will be <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2047.html">RFC 2047</a> encoded.
</dd></dl>

<code class="docutils literal notranslate">BaseHeader</code> by itself cannot be used to create a header object. It
defines a protocol that each specialized header cooperates with in order to
produce the header object. Specifically, <code class="docutils literal notranslate">BaseHeader</code> requires that
the specialized class provide a <a class="reference internal" href="functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate">classmethod()</code></a> named <code class="docutils literal notranslate">parse</code>. This
method is called as follows:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>parse(string, kwds)
</pre></div>
</div>
<code class="docutils literal notranslate">kwds</code> is a dictionary containing one pre-initialized key, <code class="docutils literal notranslate">defects</code>.
<code class="docutils literal notranslate">defects</code> is an empty list. The parse method should append any detected
defects to this list. On return, the <code class="docutils literal notranslate">kwds</code> dictionary must contain
values for at least the keys <code class="docutils literal notranslate">decoded</code> and <code class="docutils literal notranslate">defects</code>. <code class="docutils literal notranslate">decoded</code>
should be the string value for the header (that is, the header value fully
decoded to unicode). The parse method should assume that string may
contain content-transfer-encoded parts, but should correctly handle all valid
unicode characters as well so that it can parse un-encoded header values.
<code class="docutils literal notranslate">BaseHeader</code>’s <code class="docutils literal notranslate">__new__</code> then creates the header instance, and calls its
<code class="docutils literal notranslate">init</code> method. The specialized class only needs to provide an <code class="docutils literal notranslate">init</code>
method if it wishes to set additional attributes beyond those provided by
<code class="docutils literal notranslate">BaseHeader</code> itself. Such an <code class="docutils literal notranslate">init</code> method should look like this:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>def init(self, /, *args, **kw):
 self._myattr = kw.pop(&#39;myattr&#39;)
 super().init(*args, **kw)
</pre></div>
</div>
That is, anything extra that the specialized class puts in to the <code class="docutils literal notranslate">kwds</code>
dictionary should be removed and handled, and the remaining contents of
<code class="docutils literal notranslate">kw</code> (and <code class="docutils literal notranslate">args</code>) passed to the <code class="docutils literal notranslate">BaseHeader</code> <code class="docutils literal notranslate">init</code> method.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.UnstructuredHeader">
class email.headerregistry.UnstructuredHeader<a class="headerlink" href="#email.headerregistry.UnstructuredHeader" title="Permalink to this definition">¶</a></dt>
<dd>An “unstructured” header is the default type of header in <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>.
Any header that does not have a specified syntax is treated as
unstructured. The classic example of an unstructured header is the
Subject header.
In <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>, an unstructured header is a run of arbitrary text in the
ASCII character set. <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2047.html">RFC 2047</a>, however, has an <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a> compatible
mechanism for encoding non-ASCII text as ASCII characters within a header
value. When a value containing encoded words is passed to the
constructor, the <code class="docutils literal notranslate">UnstructuredHeader</code> parser converts such encoded words
into unicode, following the <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2047.html">RFC 2047</a> rules for unstructured text. The
parser uses heuristics to attempt to decode certain non-compliant encoded
words. Defects are registered in such cases, as well as defects for issues
such as invalid characters within the encoded words or the non-encoded text.
This header type provides no additional attributes.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.DateHeader">
class email.headerregistry.DateHeader<a class="headerlink" href="#email.headerregistry.DateHeader" title="Permalink to this definition">¶</a></dt>
<dd><a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a> specifies a very specific format for dates within email headers.
The <code class="docutils literal notranslate">DateHeader</code> parser recognizes that date format, as well as
recognizing a number of variant forms that are sometimes found “in the
wild”.
This header type provides the following additional attributes:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.DateHeader.datetime">
datetime<a class="headerlink" href="#email.headerregistry.DateHeader.datetime" title="Permalink to this definition">¶</a></dt>
<dd>If the header value can be recognized as a valid date of one form or
another, this attribute will contain a <a class="reference internal" href="datetime.html#datetime.datetime" title="datetime.datetime"><code class="xref py py-class docutils literal notranslate">datetime</code></a>
instance representing that date. If the timezone of the input date is
specified as <code class="docutils literal notranslate">-0000</code> (indicating it is in UTC but contains no
information about the source timezone), then <a class="reference internal" href="#email.headerregistry.DateHeader.datetime" title="email.headerregistry.DateHeader.datetime"><code class="xref py py-attr docutils literal notranslate">datetime</code></a> will be a
naive <a class="reference internal" href="datetime.html#datetime.datetime" title="datetime.datetime"><code class="xref py py-class docutils literal notranslate">datetime</code></a>. If a specific timezone offset is
found (including <code class="docutils literal notranslate">+0000</code>), then <a class="reference internal" href="#email.headerregistry.DateHeader.datetime" title="email.headerregistry.DateHeader.datetime"><code class="xref py py-attr docutils literal notranslate">datetime</code></a> will contain an aware
<code class="docutils literal notranslate">datetime</code> that uses <a class="reference internal" href="datetime.html#datetime.timezone" title="datetime.timezone"><code class="xref py py-class docutils literal notranslate">datetime.timezone</code></a> to record the timezone
offset.
</dd></dl>

The <code class="docutils literal notranslate">decoded</code> value of the header is determined by formatting the
<code class="docutils literal notranslate">datetime</code> according to the <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a> rules; that is, it is set to:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>email.utils.format_datetime(self.datetime)
</pre></div>
</div>
When creating a <code class="docutils literal notranslate">DateHeader</code>, value may be
<a class="reference internal" href="datetime.html#datetime.datetime" title="datetime.datetime"><code class="xref py py-class docutils literal notranslate">datetime</code></a> instance. This means, for example, that
the following code is valid and does what one would expect:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>msg[&#39;Date&#39;] = datetime(2011, 7, 15, 21)
</pre></div>
</div>
Because this is a naive <code class="docutils literal notranslate">datetime</code> it will be interpreted as a UTC
timestamp, and the resulting value will have a timezone of <code class="docutils literal notranslate">-0000</code>. Much
more useful is to use the <a class="reference internal" href="email.utils.html#email.utils.localtime" title="email.utils.localtime"><code class="xref py py-func docutils literal notranslate">localtime()</code></a> function from the
<a class="reference internal" href="email.utils.html#module-email.utils" title="email.utils: Miscellaneous email package utilities."><code class="xref py py-mod docutils literal notranslate">utils</code></a> module:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>msg[&#39;Date&#39;] = utils.localtime()
</pre></div>
</div>
This example sets the date header to the current time and date using
the current timezone offset.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.AddressHeader">
class email.headerregistry.AddressHeader<a class="headerlink" href="#email.headerregistry.AddressHeader" title="Permalink to this definition">¶</a></dt>
<dd>Address headers are one of the most complex structured header types.
The <code class="docutils literal notranslate">AddressHeader</code> class provides a generic interface to any address
header.
This header type provides the following additional attributes:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.AddressHeader.groups">
groups<a class="headerlink" href="#email.headerregistry.AddressHeader.groups" title="Permalink to this definition">¶</a></dt>
<dd>A tuple of <a class="reference internal" href="#email.headerregistry.Group" title="email.headerregistry.Group"><code class="xref py py-class docutils literal notranslate">Group</code></a> objects encoding the
addresses and groups found in the header value. Addresses that are
not part of a group are represented in this list as single-address
<code class="docutils literal notranslate">Groups</code> whose <a class="reference internal" href="#email.headerregistry.Group.display_name" title="email.headerregistry.Group.display_name"><code class="xref py py-attr docutils literal notranslate">display_name</code></a> is <code class="docutils literal notranslate">None</code>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.AddressHeader.addresses">
addresses<a class="headerlink" href="#email.headerregistry.AddressHeader.addresses" title="Permalink to this definition">¶</a></dt>
<dd>A tuple of <a class="reference internal" href="#email.headerregistry.Address" title="email.headerregistry.Address"><code class="xref py py-class docutils literal notranslate">Address</code></a> objects encoding all
of the individual addresses from the header value. If the header value
contains any groups, the individual addresses from the group are included
in the list at the point where the group occurs in the value (that is,
the list of addresses is “flattened” into a one dimensional list).
</dd></dl>

The <code class="docutils literal notranslate">decoded</code> value of the header will have all encoded words decoded to
unicode. <a class="reference internal" href="codecs.html#module-encodings.idna" title="encodings.idna: Internationalized Domain Names implementation"><code class="xref py py-class docutils literal notranslate">idna</code></a> encoded domain names are also decoded to
unicode. The <code class="docutils literal notranslate">decoded</code> value is set by <a class="reference internal" href="stdtypes.html#str.join" title="str.join"><code class="xref py py-attr docutils literal notranslate">join</code></a>ing the
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> value of the elements of the <code class="docutils literal notranslate">groups</code> attribute with <code class="docutils literal notranslate">',
'</code>.
A list of <a class="reference internal" href="#email.headerregistry.Address" title="email.headerregistry.Address"><code class="xref py py-class docutils literal notranslate">Address</code></a> and <a class="reference internal" href="#email.headerregistry.Group" title="email.headerregistry.Group"><code class="xref py py-class docutils literal notranslate">Group</code></a> objects in any combination
may be used to set the value of an address header. <code class="docutils literal notranslate">Group</code> objects whose
<code class="docutils literal notranslate">display_name</code> is <code class="docutils literal notranslate">None</code> will be interpreted as single addresses, which
allows an address list to be copied with groups intact by using the list
obtained from the <code class="docutils literal notranslate">groups</code> attribute of the source header.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.SingleAddressHeader">
class email.headerregistry.SingleAddressHeader<a class="headerlink" href="#email.headerregistry.SingleAddressHeader" title="Permalink to this definition">¶</a></dt>
<dd>A subclass of <a class="reference internal" href="#email.headerregistry.AddressHeader" title="email.headerregistry.AddressHeader"><code class="xref py py-class docutils literal notranslate">AddressHeader</code></a> that adds one
additional attribute:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.SingleAddressHeader.address">
address<a class="headerlink" href="#email.headerregistry.SingleAddressHeader.address" title="Permalink to this definition">¶</a></dt>
<dd>The single address encoded by the header value. If the header value
actually contains more than one address (which would be a violation of
the RFC under the default <a class="reference internal" href="email.policy.html#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>), accessing this attribute
will result in a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a>.
</dd></dl>

</dd></dl>

Many of the above classes also have a <code class="docutils literal notranslate">Unique</code> variant (for example,
<code class="docutils literal notranslate">UniqueUnstructuredHeader</code>). The only difference is that in the <code class="docutils literal notranslate">Unique</code>
variant, <a class="reference internal" href="#email.headerregistry.BaseHeader.max_count" title="email.headerregistry.BaseHeader.max_count"><code class="xref py py-attr docutils literal notranslate">max_count</code></a> is set to 1.
<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.MIMEVersionHeader">
class email.headerregistry.MIMEVersionHeader<a class="headerlink" href="#email.headerregistry.MIMEVersionHeader" title="Permalink to this definition">¶</a></dt>
<dd>There is really only one valid value for the MIME-Version
header, and that is <code class="docutils literal notranslate">1.0</code>. For future proofing, this header class
supports other valid version numbers. If a version number has a valid value
per <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2045.html">RFC 2045</a>, then the header object will have non-<code class="docutils literal notranslate">None</code> values for
the following attributes:
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.MIMEVersionHeader.version">
version<a class="headerlink" href="#email.headerregistry.MIMEVersionHeader.version" title="Permalink to this definition">¶</a></dt>
<dd>The version number as a string, with any whitespace and/or comments
removed.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.MIMEVersionHeader.major">
major<a class="headerlink" href="#email.headerregistry.MIMEVersionHeader.major" title="Permalink to this definition">¶</a></dt>
<dd>The major version number as an integer
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.MIMEVersionHeader.minor">
minor<a class="headerlink" href="#email.headerregistry.MIMEVersionHeader.minor" title="Permalink to this definition">¶</a></dt>
<dd>The minor version number as an integer
</dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.ParameterizedMIMEHeader">
class email.headerregistry.ParameterizedMIMEHeader<a class="headerlink" href="#email.headerregistry.ParameterizedMIMEHeader" title="Permalink to this definition">¶</a></dt>
<dd>MIME headers all start with the prefix ‘Content-’. Each specific header has
a certain value, described under the class for that header. Some can
also take a list of supplemental parameters, which have a common format.
This class serves as a base for all the MIME headers that take parameters.
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.ParameterizedMIMEHeader.params">
params<a class="headerlink" href="#email.headerregistry.ParameterizedMIMEHeader.params" title="Permalink to this definition">¶</a></dt>
<dd>A dictionary mapping parameter names to parameter values.
</dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.ContentTypeHeader">
class email.headerregistry.ContentTypeHeader<a class="headerlink" href="#email.headerregistry.ContentTypeHeader" title="Permalink to this definition">¶</a></dt>
<dd>A <a class="reference internal" href="#email.headerregistry.ParameterizedMIMEHeader" title="email.headerregistry.ParameterizedMIMEHeader"><code class="xref py py-class docutils literal notranslate">ParameterizedMIMEHeader</code></a> class that handles the
Content-Type header.
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.ContentTypeHeader.content_type">
content_type<a class="headerlink" href="#email.headerregistry.ContentTypeHeader.content_type" title="Permalink to this definition">¶</a></dt>
<dd>The content type string, in the form <code class="docutils literal notranslate">maintype/subtype</code>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.ContentTypeHeader.maintype">
maintype<a class="headerlink" href="#email.headerregistry.ContentTypeHeader.maintype" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.ContentTypeHeader.subtype">
subtype<a class="headerlink" href="#email.headerregistry.ContentTypeHeader.subtype" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.ContentDispositionHeader">
class email.headerregistry.ContentDispositionHeader<a class="headerlink" href="#email.headerregistry.ContentDispositionHeader" title="Permalink to this definition">¶</a></dt>
<dd>A <a class="reference internal" href="#email.headerregistry.ParameterizedMIMEHeader" title="email.headerregistry.ParameterizedMIMEHeader"><code class="xref py py-class docutils literal notranslate">ParameterizedMIMEHeader</code></a> class that handles the
Content-Disposition header.
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.ContentDispositionHeader.content_disposition">
content_disposition<a class="headerlink" href="#email.headerregistry.ContentDispositionHeader.content_disposition" title="Permalink to this definition">¶</a></dt>
<dd><code class="docutils literal notranslate">inline</code> and <code class="docutils literal notranslate">attachment</code> are the only valid values in common use.
</dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.ContentTransferEncoding">
class email.headerregistry.ContentTransferEncoding<a class="headerlink" href="#email.headerregistry.ContentTransferEncoding" title="Permalink to this definition">¶</a></dt>
<dd>Handles the Content-Transfer-Encoding header.
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.ContentTransferEncoding.cte">
cte<a class="headerlink" href="#email.headerregistry.ContentTransferEncoding.cte" title="Permalink to this definition">¶</a></dt>
<dd>Valid values are <code class="docutils literal notranslate">7bit</code>, <code class="docutils literal notranslate">8bit</code>, <code class="docutils literal notranslate">base64</code>, and
<code class="docutils literal notranslate">quoted-printable</code>. See <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2045.html">RFC 2045</a> for more information.
</dd></dl>

</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.HeaderRegistry">
class email.headerregistry.HeaderRegistry(base_class=BaseHeader, default_class=UnstructuredHeader, use_default_map=True)<a class="headerlink" href="#email.headerregistry.HeaderRegistry" title="Permalink to this definition">¶</a></dt>
<dd>This is the factory used by <a class="reference internal" href="email.policy.html#email.policy.EmailPolicy" title="email.policy.EmailPolicy"><code class="xref py py-class docutils literal notranslate">EmailPolicy</code></a> by default.
<code class="docutils literal notranslate">HeaderRegistry</code> builds the class used to create a header instance
dynamically, using base_class and a specialized class retrieved from a
registry that it holds. When a given header name does not appear in the
registry, the class specified by default_class is used as the specialized
class. When use_default_map is <code class="docutils literal notranslate">True</code> (the default), the standard
mapping of header names to classes is copied in to the registry during
initialization. base_class is always the last class in the generated
class’s <code class="docutils literal notranslate">__bases__</code> list.
The default mappings are:
<blockquote>
<div><dl class="field-list simple">
<dt class="field-odd">subject</dt>
<dd class="field-odd">UniqueUnstructuredHeader
</dd>
<dt class="field-even">date</dt>
<dd class="field-even">UniqueDateHeader
</dd>
<dt class="field-odd">resent-date</dt>
<dd class="field-odd">DateHeader
</dd>
<dt class="field-even">orig-date</dt>
<dd class="field-even">UniqueDateHeader
</dd>
<dt class="field-odd">sender</dt>
<dd class="field-odd">UniqueSingleAddressHeader
</dd>
<dt class="field-even">resent-sender</dt>
<dd class="field-even">SingleAddressHeader
</dd>
<dt class="field-odd">to</dt>
<dd class="field-odd">UniqueAddressHeader
</dd>
<dt class="field-even">resent-to</dt>
<dd class="field-even">AddressHeader
</dd>
<dt class="field-odd">cc</dt>
<dd class="field-odd">UniqueAddressHeader
</dd>
<dt class="field-even">resent-cc</dt>
<dd class="field-even">AddressHeader
</dd>
<dt class="field-odd">bcc</dt>
<dd class="field-odd">UniqueAddressHeader
</dd>
<dt class="field-even">resent-bcc</dt>
<dd class="field-even">AddressHeader
</dd>
<dt class="field-odd">from</dt>
<dd class="field-odd">UniqueAddressHeader
</dd>
<dt class="field-even">resent-from</dt>
<dd class="field-even">AddressHeader
</dd>
<dt class="field-odd">reply-to</dt>
<dd class="field-odd">UniqueAddressHeader
</dd>
<dt class="field-even">mime-version</dt>
<dd class="field-even">MIMEVersionHeader
</dd>
<dt class="field-odd">content-type</dt>
<dd class="field-odd">ContentTypeHeader
</dd>
<dt class="field-even">content-disposition</dt>
<dd class="field-even">ContentDispositionHeader
</dd>
<dt class="field-odd">content-transfer-encoding</dt>
<dd class="field-odd">ContentTransferEncodingHeader
</dd>
<dt class="field-even">message-id</dt>
<dd class="field-even">MessageIDHeader
</dd>
</dl>
</div></blockquote>
<code class="docutils literal notranslate">HeaderRegistry</code> has the following methods:
<dl class="py method">
<dt class="sig sig-object py" id="email.headerregistry.HeaderRegistry.map_to_type">
map_to_type(self, name, cls)<a class="headerlink" href="#email.headerregistry.HeaderRegistry.map_to_type" title="Permalink to this definition">¶</a></dt>
<dd>name is the name of the header to be mapped. It will be converted to
lower case in the registry. cls is the specialized class to be used,
along with base_class, to create the class used to instantiate headers
that match name.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.headerregistry.HeaderRegistry.__getitem__">
__getitem__(name)<a class="headerlink" href="#email.headerregistry.HeaderRegistry.__getitem__" title="Permalink to this definition">¶</a></dt>
<dd>Construct and return a class to handle creating a name header.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.headerregistry.HeaderRegistry.__call__">
__call__(name, value)<a class="headerlink" href="#email.headerregistry.HeaderRegistry.__call__" title="Permalink to this definition">¶</a></dt>
<dd>Retrieves the specialized header associated with name from the
registry (using default_class if name does not appear in the
registry) and composes it with base_class to produce a class,
calls the constructed class’s constructor, passing it the same
argument list, and finally returns the class instance created thereby.
</dd></dl>

</dd></dl>

The following classes are the classes used to represent data parsed from
structured headers and can, in general, be used by an application program to
construct structured values to assign to specific headers.
<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.Address">
class email.headerregistry.Address(display_name='', username='', domain='', addr_spec=None)<a class="headerlink" href="#email.headerregistry.Address" title="Permalink to this definition">¶</a></dt>
<dd>The class used to represent an email address. The general form of an
address is:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>[display_name] &lt;username@domain&gt;
</pre></div>
</div>
or:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>username@domain
</pre></div>
</div>
where each part must conform to specific syntax rules spelled out in
<a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>.
As a convenience addr_spec can be specified instead of username and
domain, in which case username and domain will be parsed from the
addr_spec. An addr_spec must be a properly RFC quoted string; if it is
not <code class="docutils literal notranslate">Address</code> will raise an error. Unicode characters are allowed and
will be property encoded when serialized. However, per the RFCs, unicode is
not allowed in the username portion of the address.
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.Address.display_name">
display_name<a class="headerlink" href="#email.headerregistry.Address.display_name" title="Permalink to this definition">¶</a></dt>
<dd>The display name portion of the address, if any, with all quoting
removed. If the address does not have a display name, this attribute
will be an empty string.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.Address.username">
username<a class="headerlink" href="#email.headerregistry.Address.username" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">username</code> portion of the address, with all quoting removed.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.Address.domain">
domain<a class="headerlink" href="#email.headerregistry.Address.domain" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">domain</code> portion of the address.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.Address.addr_spec">
addr_spec<a class="headerlink" href="#email.headerregistry.Address.addr_spec" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">username&#64;domain</code> portion of the address, correctly quoted
for use as a bare address (the second form shown above). This
attribute is not mutable.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.headerregistry.Address.__str__">
__str__()<a class="headerlink" href="#email.headerregistry.Address.__str__" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">str</code> value of the object is the address quoted according to
<a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a> rules, but with no Content Transfer Encoding of any non-ASCII
characters.
</dd></dl>

To support SMTP (<a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5321.html">RFC 5321</a>), <code class="docutils literal notranslate">Address</code> handles one special case: if
<code class="docutils literal notranslate">username</code> and <code class="docutils literal notranslate">domain</code> are both the empty string (or <code class="docutils literal notranslate">None</code>), then
the string value of the <code class="docutils literal notranslate">Address</code> is <code class="docutils literal notranslate">&lt;&gt;</code>.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="email.headerregistry.Group">
class email.headerregistry.Group(display_name=None, addresses=None)<a class="headerlink" href="#email.headerregistry.Group" title="Permalink to this definition">¶</a></dt>
<dd>The class used to represent an address group. The general form of an
address group is:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>display_name: [address-list];
</pre></div>
</div>
As a convenience for processing lists of addresses that consist of a mixture
of groups and single addresses, a <code class="docutils literal notranslate">Group</code> may also be used to represent
single addresses that are not part of a group by setting display_name to
<code class="docutils literal notranslate">None</code> and providing a list of the single address as addresses.
<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.Group.display_name">
display_name<a class="headerlink" href="#email.headerregistry.Group.display_name" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">display_name</code> of the group. If it is <code class="docutils literal notranslate">None</code> and there is
exactly one <code class="docutils literal notranslate">Address</code> in <code class="docutils literal notranslate">addresses</code>, then the <code class="docutils literal notranslate">Group</code> represents a
single address that is not in a group.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="email.headerregistry.Group.addresses">
addresses<a class="headerlink" href="#email.headerregistry.Group.addresses" title="Permalink to this definition">¶</a></dt>
<dd>A possibly empty tuple of <a class="reference internal" href="#email.headerregistry.Address" title="email.headerregistry.Address"><code class="xref py py-class docutils literal notranslate">Address</code></a> objects representing the
addresses in the group.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="email.headerregistry.Group.__str__">
__str__()<a class="headerlink" href="#email.headerregistry.Group.__str__" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">str</code> value of a <code class="docutils literal notranslate">Group</code> is formatted according to <a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc5322.html">RFC 5322</a>,
but with no Content Transfer Encoding of any non-ASCII characters. If
<code class="docutils literal notranslate">display_name</code> is none and there is a single <code class="docutils literal notranslate">Address</code> in the
<code class="docutils literal notranslate">addresses</code> list, the <code class="docutils literal notranslate">str</code> value will be the same as the <code class="docutils literal notranslate">str</code> of
that single <code class="docutils literal notranslate">Address</code>.
</dd></dl>

</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 module</a>
</dd>
</dl>
</section>

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