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<div class="section" id="module-email.headerregistry">
<span id="email-headerregistry-custom-header-objects"></span><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"><span class="pre">email.headerregistry</span></code></a>: Custom Header Objects<a class="headerlink" href="#module-email.headerregistry" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/email/headerregistry.py">Lib/email/headerregistry.py</a></p>
<hr class="docutils" />
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6: </span><a class="footnote-reference brackets" href="#id2" id="id1">1</a></p>
</div>
<p>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"><span class="pre">str</span></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"><span class="pre">header_factory</span></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"><span class="pre">policy</span></code></a> in
effect when the headers are created. This section documents the particular
<code class="docutils literal notranslate"><span class="pre">header_factory</span></code> implemented by the email package for handling <span class="target" id="index-0"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></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.</p>
<p>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"><span class="pre">EmailPolicy</span></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"><span class="pre">HeaderRegistry</span></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"><span class="pre">BaseHeader</span></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"><span class="pre">UnstructuredHeader</span></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"><span class="pre">HeaderRegistry</span></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.</p>
<p>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"><span class="pre">HeaderRegistry</span></code></a>, and
finally the support classes used to represent the data parsed from structured
headers.</p>
<dl class="class">
<dt id="email.headerregistry.BaseHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">BaseHeader</code><span class="sig-paren">(</span><em class="sig-param">name</em>, <em class="sig-param">value</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.BaseHeader" title="Permalink to this definition">¶</a></dt>
<dd><p><em>name</em> and <em>value</em> are passed to <code class="docutils literal notranslate"><span class="pre">BaseHeader</span></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"><span class="pre">header_factory</span></code></a> call. The string value of
any header object is the <em>value</em> fully decoded to unicode.</p>
<p>This base class defines the following read-only properties:</p>
<dl class="attribute">
<dt id="email.headerregistry.BaseHeader.name">
<code class="sig-name descname">name</code><a class="headerlink" href="#email.headerregistry.BaseHeader.name" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><span class="pre">header_factory</span></code></a> call for <em>name</em>; that
is, case is preserved.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.BaseHeader.defects">
<code class="sig-name descname">defects</code><a class="headerlink" href="#email.headerregistry.BaseHeader.defects" title="Permalink to this definition">¶</a></dt>
<dd><p>A tuple of <code class="xref py py-exc docutils literal notranslate"><span class="pre">HeaderDefect</span></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"><span class="pre">errors</span></code></a>
module for a discussion of the types of defects that may be reported.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.BaseHeader.max_count">
<code class="sig-name descname">max_count</code><a class="headerlink" href="#email.headerregistry.BaseHeader.max_count" title="Permalink to this definition">¶</a></dt>
<dd><p>The maximum number of headers of this type that can have the same
<code class="docutils literal notranslate"><span class="pre">name</span></code>. A value of <code class="docutils literal notranslate"><span class="pre">None</span></code> means unlimited. The <code class="docutils literal notranslate"><span class="pre">BaseHeader</span></code> value
for this attribute is <code class="docutils literal notranslate"><span class="pre">None</span></code>; it is expected that specialized header
classes will override this value as needed.</p>
</dd></dl>
<p><code class="docutils literal notranslate"><span class="pre">BaseHeader</span></code> also provides the following method, which is called by the
email library code and should not in general be called by application
programs:</p>
<dl class="method">
<dt id="email.headerregistry.BaseHeader.fold">
<code class="sig-name descname">fold</code><span class="sig-paren">(</span><em class="sig-param">*</em>, <em class="sig-param">policy</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.BaseHeader.fold" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><span class="pre">linesep</span></code></a>
characters as required to correctly fold the header according to
<em>policy</em>. 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"><span class="pre">cte_type</span></code></a> of <code class="docutils literal notranslate"><span class="pre">8bit</span></code> will be
treated as if it were <code class="docutils literal notranslate"><span class="pre">7bit</span></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"><span class="pre">utf8</span></code></a> is <code class="docutils literal notranslate"><span class="pre">False</span></code>,
non-ASCII data will be <span class="target" id="index-1"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2047.html"><strong>RFC 2047</strong></a> encoded.</p>
</dd></dl>
<p><code class="docutils literal notranslate"><span class="pre">BaseHeader</span></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"><span class="pre">BaseHeader</span></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"><span class="pre">classmethod()</span></code></a> named <code class="docutils literal notranslate"><span class="pre">parse</span></code>. This
method is called as follows:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">parse</span><span class="p">(</span><span class="n">string</span><span class="p">,</span> <span class="n">kwds</span><span class="p">)</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">kwds</span></code> is a dictionary containing one pre-initialized key, <code class="docutils literal notranslate"><span class="pre">defects</span></code>.
<code class="docutils literal notranslate"><span class="pre">defects</span></code> is an empty list. The parse method should append any detected
defects to this list. On return, the <code class="docutils literal notranslate"><span class="pre">kwds</span></code> dictionary <em>must</em> contain
values for at least the keys <code class="docutils literal notranslate"><span class="pre">decoded</span></code> and <code class="docutils literal notranslate"><span class="pre">defects</span></code>. <code class="docutils literal notranslate"><span class="pre">decoded</span></code>
should be the string value for the header (that is, the header value fully
decoded to unicode). The parse method should assume that <em>string</em> 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.</p>
<p><code class="docutils literal notranslate"><span class="pre">BaseHeader</span></code>’s <code class="docutils literal notranslate"><span class="pre">__new__</span></code> then creates the header instance, and calls its
<code class="docutils literal notranslate"><span class="pre">init</span></code> method. The specialized class only needs to provide an <code class="docutils literal notranslate"><span class="pre">init</span></code>
method if it wishes to set additional attributes beyond those provided by
<code class="docutils literal notranslate"><span class="pre">BaseHeader</span></code> itself. Such an <code class="docutils literal notranslate"><span class="pre">init</span></code> method should look like this:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">init</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_myattr</span> <span class="o">=</span> <span class="n">kw</span><span class="o">.</span><span class="n">pop</span><span class="p">(</span><span class="s1">'myattr'</span><span class="p">)</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="n">init</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kw</span><span class="p">)</span>
</pre></div>
</div>
<p>That is, anything extra that the specialized class puts in to the <code class="docutils literal notranslate"><span class="pre">kwds</span></code>
dictionary should be removed and handled, and the remaining contents of
<code class="docutils literal notranslate"><span class="pre">kw</span></code> (and <code class="docutils literal notranslate"><span class="pre">args</span></code>) passed to the <code class="docutils literal notranslate"><span class="pre">BaseHeader</span></code> <code class="docutils literal notranslate"><span class="pre">init</span></code> method.</p>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.UnstructuredHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">UnstructuredHeader</code><a class="headerlink" href="#email.headerregistry.UnstructuredHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>An “unstructured” header is the default type of header in <span class="target" id="index-2"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a>.
Any header that does not have a specified syntax is treated as
unstructured. The classic example of an unstructured header is the
<em class="mailheader">Subject</em> header.</p>
<p>In <span class="target" id="index-3"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a>, an unstructured header is a run of arbitrary text in the
ASCII character set. <span class="target" id="index-4"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2047.html"><strong>RFC 2047</strong></a>, however, has an <span class="target" id="index-5"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a> compatible
mechanism for encoding non-ASCII text as ASCII characters within a header
value. When a <em>value</em> containing encoded words is passed to the
constructor, the <code class="docutils literal notranslate"><span class="pre">UnstructuredHeader</span></code> parser converts such encoded words
into unicode, following the <span class="target" id="index-6"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2047.html"><strong>RFC 2047</strong></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.</p>
<p>This header type provides no additional attributes.</p>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.DateHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">DateHeader</code><a class="headerlink" href="#email.headerregistry.DateHeader" title="Permalink to this definition">¶</a></dt>
<dd><p><span class="target" id="index-7"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a> specifies a very specific format for dates within email headers.
The <code class="docutils literal notranslate"><span class="pre">DateHeader</span></code> parser recognizes that date format, as well as
recognizing a number of variant forms that are sometimes found “in the
wild”.</p>
<p>This header type provides the following additional attributes:</p>
<dl class="attribute">
<dt id="email.headerregistry.DateHeader.datetime">
<code class="sig-name descname">datetime</code><a class="headerlink" href="#email.headerregistry.DateHeader.datetime" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><span class="pre">datetime</span></code></a>
instance representing that date. If the timezone of the input date is
specified as <code class="docutils literal notranslate"><span class="pre">-0000</span></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"><span class="pre">datetime</span></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"><span class="pre">datetime</span></code></a>. If a specific timezone offset is
found (including <cite>+0000</cite>), then <a class="reference internal" href="#email.headerregistry.DateHeader.datetime" title="email.headerregistry.DateHeader.datetime"><code class="xref py py-attr docutils literal notranslate"><span class="pre">datetime</span></code></a> will contain an aware
<code class="docutils literal notranslate"><span class="pre">datetime</span></code> that uses <a class="reference internal" href="datetime.html#datetime.timezone" title="datetime.timezone"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime.timezone</span></code></a> to record the timezone
offset.</p>
</dd></dl>
<p>The <code class="docutils literal notranslate"><span class="pre">decoded</span></code> value of the header is determined by formatting the
<code class="docutils literal notranslate"><span class="pre">datetime</span></code> according to the <span class="target" id="index-8"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a> rules; that is, it is set to:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">email</span><span class="o">.</span><span class="n">utils</span><span class="o">.</span><span class="n">format_datetime</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">datetime</span><span class="p">)</span>
</pre></div>
</div>
<p>When creating a <code class="docutils literal notranslate"><span class="pre">DateHeader</span></code>, <em>value</em> may be
<a class="reference internal" href="datetime.html#datetime.datetime" title="datetime.datetime"><code class="xref py py-class docutils literal notranslate"><span class="pre">datetime</span></code></a> instance. This means, for example, that
the following code is valid and does what one would expect:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">msg</span><span class="p">[</span><span class="s1">'Date'</span><span class="p">]</span> <span class="o">=</span> <span class="n">datetime</span><span class="p">(</span><span class="mi">2011</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">15</span><span class="p">,</span> <span class="mi">21</span><span class="p">)</span>
</pre></div>
</div>
<p>Because this is a naive <code class="docutils literal notranslate"><span class="pre">datetime</span></code> it will be interpreted as a UTC
timestamp, and the resulting value will have a timezone of <code class="docutils literal notranslate"><span class="pre">-0000</span></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"><span class="pre">localtime()</span></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"><span class="pre">utils</span></code></a> module:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">msg</span><span class="p">[</span><span class="s1">'Date'</span><span class="p">]</span> <span class="o">=</span> <span class="n">utils</span><span class="o">.</span><span class="n">localtime</span><span class="p">()</span>
</pre></div>
</div>
<p>This example sets the date header to the current time and date using
the current timezone offset.</p>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.AddressHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">AddressHeader</code><a class="headerlink" href="#email.headerregistry.AddressHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>Address headers are one of the most complex structured header types.
The <code class="docutils literal notranslate"><span class="pre">AddressHeader</span></code> class provides a generic interface to any address
header.</p>
<p>This header type provides the following additional attributes:</p>
<dl class="attribute">
<dt id="email.headerregistry.AddressHeader.groups">
<code class="sig-name descname">groups</code><a class="headerlink" href="#email.headerregistry.AddressHeader.groups" title="Permalink to this definition">¶</a></dt>
<dd><p>A tuple of <a class="reference internal" href="#email.headerregistry.Group" title="email.headerregistry.Group"><code class="xref py py-class docutils literal notranslate"><span class="pre">Group</span></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"><span class="pre">Groups</span></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"><span class="pre">display_name</span></code></a> is <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.AddressHeader.addresses">
<code class="sig-name descname">addresses</code><a class="headerlink" href="#email.headerregistry.AddressHeader.addresses" title="Permalink to this definition">¶</a></dt>
<dd><p>A tuple of <a class="reference internal" href="#email.headerregistry.Address" title="email.headerregistry.Address"><code class="xref py py-class docutils literal notranslate"><span class="pre">Address</span></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).</p>
</dd></dl>
<p>The <code class="docutils literal notranslate"><span class="pre">decoded</span></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"><span class="pre">idna</span></code></a> encoded domain names are also decoded to
unicode. The <code class="docutils literal notranslate"><span class="pre">decoded</span></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"><span class="pre">join</span></code></a>ing the
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> value of the elements of the <code class="docutils literal notranslate"><span class="pre">groups</span></code> attribute with <code class="docutils literal notranslate"><span class="pre">',</span>
<span class="pre">'</span></code>.</p>
<p>A list of <a class="reference internal" href="#email.headerregistry.Address" title="email.headerregistry.Address"><code class="xref py py-class docutils literal notranslate"><span class="pre">Address</span></code></a> and <a class="reference internal" href="#email.headerregistry.Group" title="email.headerregistry.Group"><code class="xref py py-class docutils literal notranslate"><span class="pre">Group</span></code></a> objects in any combination
may be used to set the value of an address header. <code class="docutils literal notranslate"><span class="pre">Group</span></code> objects whose
<code class="docutils literal notranslate"><span class="pre">display_name</span></code> is <code class="docutils literal notranslate"><span class="pre">None</span></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"><span class="pre">groups</span></code> attribute of the source header.</p>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.SingleAddressHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">SingleAddressHeader</code><a class="headerlink" href="#email.headerregistry.SingleAddressHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>A subclass of <a class="reference internal" href="#email.headerregistry.AddressHeader" title="email.headerregistry.AddressHeader"><code class="xref py py-class docutils literal notranslate"><span class="pre">AddressHeader</span></code></a> that adds one
additional attribute:</p>
<dl class="attribute">
<dt id="email.headerregistry.SingleAddressHeader.address">
<code class="sig-name descname">address</code><a class="headerlink" href="#email.headerregistry.SingleAddressHeader.address" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><span class="pre">policy</span></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"><span class="pre">ValueError</span></code></a>.</p>
</dd></dl>
</dd></dl>
<p>Many of the above classes also have a <code class="docutils literal notranslate"><span class="pre">Unique</span></code> variant (for example,
<code class="docutils literal notranslate"><span class="pre">UniqueUnstructuredHeader</span></code>). The only difference is that in the <code class="docutils literal notranslate"><span class="pre">Unique</span></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"><span class="pre">max_count</span></code></a> is set to 1.</p>
<dl class="class">
<dt id="email.headerregistry.MIMEVersionHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">MIMEVersionHeader</code><a class="headerlink" href="#email.headerregistry.MIMEVersionHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>There is really only one valid value for the <em class="mailheader">MIME-Version</em>
header, and that is <code class="docutils literal notranslate"><span class="pre">1.0</span></code>. For future proofing, this header class
supports other valid version numbers. If a version number has a valid value
per <span class="target" id="index-9"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2045.html"><strong>RFC 2045</strong></a>, then the header object will have non-<code class="docutils literal notranslate"><span class="pre">None</span></code> values for
the following attributes:</p>
<dl class="attribute">
<dt id="email.headerregistry.MIMEVersionHeader.version">
<code class="sig-name descname">version</code><a class="headerlink" href="#email.headerregistry.MIMEVersionHeader.version" title="Permalink to this definition">¶</a></dt>
<dd><p>The version number as a string, with any whitespace and/or comments
removed.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.MIMEVersionHeader.major">
<code class="sig-name descname">major</code><a class="headerlink" href="#email.headerregistry.MIMEVersionHeader.major" title="Permalink to this definition">¶</a></dt>
<dd><p>The major version number as an integer</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.MIMEVersionHeader.minor">
<code class="sig-name descname">minor</code><a class="headerlink" href="#email.headerregistry.MIMEVersionHeader.minor" title="Permalink to this definition">¶</a></dt>
<dd><p>The minor version number as an integer</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.ParameterizedMIMEHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">ParameterizedMIMEHeader</code><a class="headerlink" href="#email.headerregistry.ParameterizedMIMEHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>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.</p>
<dl class="attribute">
<dt id="email.headerregistry.ParameterizedMIMEHeader.params">
<code class="sig-name descname">params</code><a class="headerlink" href="#email.headerregistry.ParameterizedMIMEHeader.params" title="Permalink to this definition">¶</a></dt>
<dd><p>A dictionary mapping parameter names to parameter values.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.ContentTypeHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">ContentTypeHeader</code><a class="headerlink" href="#email.headerregistry.ContentTypeHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="#email.headerregistry.ParameterizedMIMEHeader" title="email.headerregistry.ParameterizedMIMEHeader"><code class="xref py py-class docutils literal notranslate"><span class="pre">ParameterizedMIMEHeader</span></code></a> class that handles the
<em class="mailheader">Content-Type</em> header.</p>
<dl class="attribute">
<dt id="email.headerregistry.ContentTypeHeader.content_type">
<code class="sig-name descname">content_type</code><a class="headerlink" href="#email.headerregistry.ContentTypeHeader.content_type" title="Permalink to this definition">¶</a></dt>
<dd><p>The content type string, in the form <code class="docutils literal notranslate"><span class="pre">maintype/subtype</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.ContentTypeHeader.maintype">
<code class="sig-name descname">maintype</code><a class="headerlink" href="#email.headerregistry.ContentTypeHeader.maintype" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.ContentTypeHeader.subtype">
<code class="sig-name descname">subtype</code><a class="headerlink" href="#email.headerregistry.ContentTypeHeader.subtype" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.ContentDispositionHeader">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">ContentDispositionHeader</code><a class="headerlink" href="#email.headerregistry.ContentDispositionHeader" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="#email.headerregistry.ParameterizedMIMEHeader" title="email.headerregistry.ParameterizedMIMEHeader"><code class="xref py py-class docutils literal notranslate"><span class="pre">ParameterizedMIMEHeader</span></code></a> class that handles the
<em class="mailheader">Content-Disposition</em> header.</p>
<dl class="attribute">
<dt>
<code class="sig-name descname">content-disposition</code></dt>
<dd><p><code class="docutils literal notranslate"><span class="pre">inline</span></code> and <code class="docutils literal notranslate"><span class="pre">attachment</span></code> are the only valid values in common use.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.ContentTransferEncoding">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">ContentTransferEncoding</code><a class="headerlink" href="#email.headerregistry.ContentTransferEncoding" title="Permalink to this definition">¶</a></dt>
<dd><p>Handles the <em class="mailheader">Content-Transfer-Encoding</em> header.</p>
<dl class="attribute">
<dt id="email.headerregistry.ContentTransferEncoding.cte">
<code class="sig-name descname">cte</code><a class="headerlink" href="#email.headerregistry.ContentTransferEncoding.cte" title="Permalink to this definition">¶</a></dt>
<dd><p>Valid values are <code class="docutils literal notranslate"><span class="pre">7bit</span></code>, <code class="docutils literal notranslate"><span class="pre">8bit</span></code>, <code class="docutils literal notranslate"><span class="pre">base64</span></code>, and
<code class="docutils literal notranslate"><span class="pre">quoted-printable</span></code>. See <span class="target" id="index-10"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2045.html"><strong>RFC 2045</strong></a> for more information.</p>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.HeaderRegistry">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">HeaderRegistry</code><span class="sig-paren">(</span><em class="sig-param">base_class=BaseHeader</em>, <em class="sig-param">default_class=UnstructuredHeader</em>, <em class="sig-param">use_default_map=True</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.HeaderRegistry" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><span class="pre">EmailPolicy</span></code></a> by default.
<code class="docutils literal notranslate"><span class="pre">HeaderRegistry</span></code> builds the class used to create a header instance
dynamically, using <em>base_class</em> 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 <em>default_class</em> is used as the specialized
class. When <em>use_default_map</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code> (the default), the standard
mapping of header names to classes is copied in to the registry during
initialization. <em>base_class</em> is always the last class in the generated
class’s <code class="docutils literal notranslate"><span class="pre">__bases__</span></code> list.</p>
<p>The default mappings are:</p>
<blockquote>
<div><dl class="field-list simple">
<dt class="field-odd">subject</dt>
<dd class="field-odd"><p>UniqueUnstructuredHeader</p>
</dd>
<dt class="field-even">date</dt>
<dd class="field-even"><p>UniqueDateHeader</p>
</dd>
<dt class="field-odd">resent-date</dt>
<dd class="field-odd"><p>DateHeader</p>
</dd>
<dt class="field-even">orig-date</dt>
<dd class="field-even"><p>UniqueDateHeader</p>
</dd>
<dt class="field-odd">sender</dt>
<dd class="field-odd"><p>UniqueSingleAddressHeader</p>
</dd>
<dt class="field-even">resent-sender</dt>
<dd class="field-even"><p>SingleAddressHeader</p>
</dd>
<dt class="field-odd">to</dt>
<dd class="field-odd"><p>UniqueAddressHeader</p>
</dd>
<dt class="field-even">resent-to</dt>
<dd class="field-even"><p>AddressHeader</p>
</dd>
<dt class="field-odd">cc</dt>
<dd class="field-odd"><p>UniqueAddressHeader</p>
</dd>
<dt class="field-even">resent-cc</dt>
<dd class="field-even"><p>AddressHeader</p>
</dd>
<dt class="field-odd">from</dt>
<dd class="field-odd"><p>UniqueAddressHeader</p>
</dd>
<dt class="field-even">resent-from</dt>
<dd class="field-even"><p>AddressHeader</p>
</dd>
<dt class="field-odd">reply-to</dt>
<dd class="field-odd"><p>UniqueAddressHeader</p>
</dd>
</dl>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">HeaderRegistry</span></code> has the following methods:</p>
<dl class="method">
<dt id="email.headerregistry.HeaderRegistry.map_to_type">
<code class="sig-name descname">map_to_type</code><span class="sig-paren">(</span><em class="sig-param">self</em>, <em class="sig-param">name</em>, <em class="sig-param">cls</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.HeaderRegistry.map_to_type" title="Permalink to this definition">¶</a></dt>
<dd><p><em>name</em> is the name of the header to be mapped. It will be converted to
lower case in the registry. <em>cls</em> is the specialized class to be used,
along with <em>base_class</em>, to create the class used to instantiate headers
that match <em>name</em>.</p>
</dd></dl>
<dl class="method">
<dt id="email.headerregistry.HeaderRegistry.__getitem__">
<code class="sig-name descname">__getitem__</code><span class="sig-paren">(</span><em class="sig-param">name</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.HeaderRegistry.__getitem__" title="Permalink to this definition">¶</a></dt>
<dd><p>Construct and return a class to handle creating a <em>name</em> header.</p>
</dd></dl>
<dl class="method">
<dt id="email.headerregistry.HeaderRegistry.__call__">
<code class="sig-name descname">__call__</code><span class="sig-paren">(</span><em class="sig-param">name</em>, <em class="sig-param">value</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.HeaderRegistry.__call__" title="Permalink to this definition">¶</a></dt>
<dd><p>Retrieves the specialized header associated with <em>name</em> from the
registry (using <em>default_class</em> if <em>name</em> does not appear in the
registry) and composes it with <em>base_class</em> to produce a class,
calls the constructed class’s constructor, passing it the same
argument list, and finally returns the class instance created thereby.</p>
</dd></dl>
</dd></dl>
<p>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.</p>
<dl class="class">
<dt id="email.headerregistry.Address">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">Address</code><span class="sig-paren">(</span><em class="sig-param">display_name=''</em>, <em class="sig-param">username=''</em>, <em class="sig-param">domain=''</em>, <em class="sig-param">addr_spec=None</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.Address" title="Permalink to this definition">¶</a></dt>
<dd><p>The class used to represent an email address. The general form of an
address is:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">display_name</span><span class="p">]</span> <span class="o"><</span><span class="n">username</span><span class="nd">@domain</span><span class="o">></span>
</pre></div>
</div>
<p>or:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">username</span><span class="nd">@domain</span>
</pre></div>
</div>
<p>where each part must conform to specific syntax rules spelled out in
<span class="target" id="index-11"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a>.</p>
<p>As a convenience <em>addr_spec</em> can be specified instead of <em>username</em> and
<em>domain</em>, in which case <em>username</em> and <em>domain</em> will be parsed from the
<em>addr_spec</em>. An <em>addr_spec</em> must be a properly RFC quoted string; if it is
not <code class="docutils literal notranslate"><span class="pre">Address</span></code> will raise an error. Unicode characters are allowed and
will be property encoded when serialized. However, per the RFCs, unicode is
<em>not</em> allowed in the username portion of the address.</p>
<dl class="attribute">
<dt id="email.headerregistry.Address.display_name">
<code class="sig-name descname">display_name</code><a class="headerlink" href="#email.headerregistry.Address.display_name" title="Permalink to this definition">¶</a></dt>
<dd><p>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.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.Address.username">
<code class="sig-name descname">username</code><a class="headerlink" href="#email.headerregistry.Address.username" title="Permalink to this definition">¶</a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">username</span></code> portion of the address, with all quoting removed.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.Address.domain">
<code class="sig-name descname">domain</code><a class="headerlink" href="#email.headerregistry.Address.domain" title="Permalink to this definition">¶</a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">domain</span></code> portion of the address.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.Address.addr_spec">
<code class="sig-name descname">addr_spec</code><a class="headerlink" href="#email.headerregistry.Address.addr_spec" title="Permalink to this definition">¶</a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">username@domain</span></code> portion of the address, correctly quoted
for use as a bare address (the second form shown above). This
attribute is not mutable.</p>
</dd></dl>
<dl class="method">
<dt id="email.headerregistry.Address.__str__">
<code class="sig-name descname">__str__</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.Address.__str__" title="Permalink to this definition">¶</a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">str</span></code> value of the object is the address quoted according to
<span class="target" id="index-12"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a> rules, but with no Content Transfer Encoding of any non-ASCII
characters.</p>
</dd></dl>
<p>To support SMTP (<span class="target" id="index-13"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5321.html"><strong>RFC 5321</strong></a>), <code class="docutils literal notranslate"><span class="pre">Address</span></code> handles one special case: if
<code class="docutils literal notranslate"><span class="pre">username</span></code> and <code class="docutils literal notranslate"><span class="pre">domain</span></code> are both the empty string (or <code class="docutils literal notranslate"><span class="pre">None</span></code>), then
the string value of the <code class="docutils literal notranslate"><span class="pre">Address</span></code> is <code class="docutils literal notranslate"><span class="pre"><></span></code>.</p>
</dd></dl>
<dl class="class">
<dt id="email.headerregistry.Group">
<em class="property">class </em><code class="sig-prename descclassname">email.headerregistry.</code><code class="sig-name descname">Group</code><span class="sig-paren">(</span><em class="sig-param">display_name=None</em>, <em class="sig-param">addresses=None</em><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.Group" title="Permalink to this definition">¶</a></dt>
<dd><p>The class used to represent an address group. The general form of an
address group is:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">display_name</span><span class="p">:</span> <span class="p">[</span><span class="n">address</span><span class="o">-</span><span class="nb">list</span><span class="p">];</span>
</pre></div>
</div>
<p>As a convenience for processing lists of addresses that consist of a mixture
of groups and single addresses, a <code class="docutils literal notranslate"><span class="pre">Group</span></code> may also be used to represent
single addresses that are not part of a group by setting <em>display_name</em> to
<code class="docutils literal notranslate"><span class="pre">None</span></code> and providing a list of the single address as <em>addresses</em>.</p>
<dl class="attribute">
<dt id="email.headerregistry.Group.display_name">
<code class="sig-name descname">display_name</code><a class="headerlink" href="#email.headerregistry.Group.display_name" title="Permalink to this definition">¶</a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">display_name</span></code> of the group. If it is <code class="docutils literal notranslate"><span class="pre">None</span></code> and there is
exactly one <code class="docutils literal notranslate"><span class="pre">Address</span></code> in <code class="docutils literal notranslate"><span class="pre">addresses</span></code>, then the <code class="docutils literal notranslate"><span class="pre">Group</span></code> represents a
single address that is not in a group.</p>
</dd></dl>
<dl class="attribute">
<dt id="email.headerregistry.Group.addresses">
<code class="sig-name descname">addresses</code><a class="headerlink" href="#email.headerregistry.Group.addresses" title="Permalink to this definition">¶</a></dt>
<dd><p>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"><span class="pre">Address</span></code></a> objects representing the
addresses in the group.</p>
</dd></dl>
<dl class="method">
<dt id="email.headerregistry.Group.__str__">
<code class="sig-name descname">__str__</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#email.headerregistry.Group.__str__" title="Permalink to this definition">¶</a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">str</span></code> value of a <code class="docutils literal notranslate"><span class="pre">Group</span></code> is formatted according to <span class="target" id="index-14"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5322.html"><strong>RFC 5322</strong></a>,
but with no Content Transfer Encoding of any non-ASCII characters. If
<code class="docutils literal notranslate"><span class="pre">display_name</span></code> is none and there is a single <code class="docutils literal notranslate"><span class="pre">Address</span></code> in the
<code class="docutils literal notranslate"><span class="pre">addresses</span></code> list, the <code class="docutils literal notranslate"><span class="pre">str</span></code> value will be the same as the <code class="docutils literal notranslate"><span class="pre">str</span></code> of
that single <code class="docutils literal notranslate"><span class="pre">Address</span></code>.</p>
</dd></dl>
</dd></dl>
<p class="rubric">Footnotes</p>
<dl class="footnote brackets">
<dt class="label" id="id2"><span class="brackets"><a class="fn-backref" href="#id1">1</a></span></dt>
<dd><p>Originally added in 3.3 as a <a class="reference internal" href="../glossary.html#term-provisional-package"><span class="xref std std-term">provisional module</span></a></p>
</dd>
</dl>
</div>
</div>
</div>
</div>
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