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Lib/email/mime/base.py

Source:

cpython 3.14 @ ab2d84fe1023/Lib/email/mime/base.py

Lib/email/mime/base.py defines MIMEBase, the root of the MIME class hierarchy, and MIMENonMultipart, a guard subclass that prevents attaching sub-parts to leaf message types. All concrete MIME classes (MIMEText, MIMEImage, MIMEApplication, etc.) ultimately inherit from MIMEBase.

Map​

LinesSymbolRole
1-10importsmessage.Message, errors
12-35MIMEBaseSets Content-Type header; wraps add_header
37-40MIMENonMultipartRaises MultipartConversionError on attach()

Reading​

MIMEBase constructor​

MIMEBase.__init__ calls Message.__init__ and then adds the Content-Type header using the _maintype and _subtype arguments. Additional keyword arguments are passed to Message.add_header as MIME parameters.

# CPython: Lib/email/mime/base.py:12 MIMEBase.__init__
class MIMEBase(message.Message):
    def __init__(self, _maintype, _subtype, *, policy=None, **_params):
        if policy is None:
            from email.policy import compat32
            policy = compat32
        message.Message.__init__(self, policy=policy)
        ctype = '%s/%s' % (_maintype, _subtype)
        self.add_header('Content-Type', ctype, **_params)
        if 'MIME-Version' not in self:
            self.add_header('MIME-Version', '1.0')

MIMENonMultipart attach guard​

MIMENonMultipart is a mixin that raises MultipartConversionError if code tries to call attach() on a non-multipart part. This makes programming errors explicit rather than silently producing malformed messages.

# CPython: Lib/email/mime/base.py:37 MIMENonMultipart.attach
class MIMENonMultipart(MIMEBase):
    def attach(self, payload):
        raise errors.MultipartConversionError(
            'Cannot attach additional subparts to non-multipart/*')

Content-Type parameter encoding​

Message.add_header (called from MIMEBase.__init__) handles RFC 2231 parameter encoding for non-ASCII values in MIME parameters like name or filename. Parameters are passed as keyword arguments with underscores replaced by hyphens.

gopy notes​

Not yet ported. The planned package path is module/email/mime/. In Go the hierarchy maps to a struct embedding chain; MIMEBase functionality maps to methods on the base Message struct that set the Content-Type header on construction.