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Unified Diff: Doc/library/email.policy.rst

Issue 10839: email module should not allow some header field repetitions
Patch Set: Created 7 years, 10 months ago
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--- a/Doc/library/email.policy.rst
+++ b/Doc/library/email.policy.rst
@@ -196,6 +196,25 @@
custom ``Message`` objects) should also provide such an attribute,
otherwise defects in parsed messages will raise unexpected errors.
+ .. method:: header_max_count(name)
+
+ Return the maximum allowed number of headers named *name*.
+
+ Called when a header is added to a :class:`~email.message.Message`
+ object. If the returned value is not ``0`` or ``None``, and there are
+ already a number of headers with the name *name* equal to the value
+ returned, a :exc:`ValueError` is raised.
+
+ Because the default behavior of ``Message.__setitem__`` 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
+ ``Message`` 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 ``None`` for all header names.
+
.. method:: header_source_parse(sourcelines)
The email package calls this method with a list of strings, each string
@@ -366,6 +385,12 @@
The class provides the following concrete implementations of the abstract
methods of :class:`Policy`:
+ .. method:: header_max_count(name)
+
+ Returns the value of the
+ :attr:`~email.headerregistry.BaseHeader.max_count` attribute of the
+ specialized class used to represent the header with the given name.
+
.. method:: header_source_parse(sourcelines)
The implementation of this method is the same as that for the
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