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This module provides a class Charset for representing character sets
and character set conversions in email messages, as well as a character set registry and
several convenience methods for manipulating this registry. Instances of Charset
are used in several other modules within the email package.
New in version 2.2.2.
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| class Charset( |
[input_charset]) |
- Map character sets to their email properties.
This class provides information about the requirements imposed on email for a specific
character set. It also provides convenience routines for converting between character
sets, given the availability of the applicable codecs. Given a character set, it will do
its best to provide information on how to use that character set in an email message in an
RFC-compliant way.
Certain character sets must be encoded with quoted-printable or base64 when used in
email headers or bodies. Certain character sets must be converted outright, and are not
allowed in email.
Optional input_charset is as described below; it is always coerced to lower
case. After being alias normalized it is also used as a lookup into the registry of
character sets to find out the header encoding, body encoding, and output conversion codec
to be used for the character set. For example, if input_charset is iso-8859-1,
then headers and bodies will be encoded using quoted-printable and no output conversion
codec is necessary. If input_charset is euc-jp, then headers will
be encoded with base64, bodies will not be encoded, but output text will be converted from
the euc-jp character set to the iso-2022-jp character set.
Charset instances have the following data attributes:
- input_charset
- The initial character set specified. Common aliases are converted to their official
email names (e.g.
latin_1 is converted to iso-8859-1). Defaults
to 7-bit us-ascii.
- header_encoding
- If the character set must be encoded before it can be used in an email header, this
attribute will be set to
Charset.QP (for quoted-printable), Charset.BASE64
(for base64 encoding), or Charset.SHORTEST for the shortest of QP or BASE64
encoding. Otherwise, it will be None.
- body_encoding
- Same as header_encoding, but describes the encoding for the mail message's
body, which indeed may be different than the header encoding.
Charset.SHORTEST
is not allowed for body_encoding.
- output_charset
- Some character sets must be converted before they can be used in email headers or
bodies. If the input_charset is one of them, this attribute will contain the
name of the character set output will be converted to. Otherwise, it will be
None.
- input_codec
- The name of the Python codec used to convert the input_charset to Unicode. If
no conversion codec is necessary, this attribute will be
None.
- output_codec
- The name of the Python codec used to convert Unicode to the output_charset.
If no conversion codec is necessary, this attribute will have the same value as the input_codec.
Charset instances also have the following methods:
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- Return the content transfer encoding used for body encoding.
This is either the string "quoted-printable" or "base64"depending on the encoding used, or it is a function, in
which case you should call the function with a single argument, the Message object being
encoded. The function should then set the
header itself to whatever is appropriate.
Returns the string "quoted-printable" if body_encoding
is QP, returns the string "base64" if body_encoding
is BASE64, and returns the string "7bit"
otherwise.
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- Convert the string s from the input_codec to the output_codec.
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- Convert a possibly multibyte string to a safely splittable format. s is the
string to split.
Uses the input_codec to try and convert the string to Unicode, so it can be
safely split on character boundaries (even for multibyte characters).
Returns the string as-is if it isn't known how to convert s to Unicode with
the input_charset.
Characters that could not be converted to Unicode will be replaced with the Unicode
replacement character "U+FFFD".
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| from_splittable( |
ustr[, to_output]) |
- Convert a splittable string back into an encoded string. ustr is a Unicode
string to ``unsplit''.
This method uses the proper codec to try and convert the string from Unicode back into
an encoded format. Return the string as-is if it is not Unicode, or if it could not be
converted from Unicode.
Characters that could not be converted from Unicode will be replaced with an
appropriate character (usually "?").
If to_output is True (the default), uses output_codec
to convert to an encoded format. If to_output is False, it uses input_codec.
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- Return the output character set.
This is the output_charset attribute if that is not None,
otherwise it is input_charset.
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- Return the length of the encoded header string, properly calculating for
quoted-printable or base64 encoding.
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| header_encode( |
s[, convert]) |
- Header-encode the string s.
If convert is True, the string will be converted from the input
charset to the output charset automatically. This is not useful for multibyte character
sets, which have line length issues (multibyte characters must be split on a character,
not a byte boundary); use the higher-level Header class to deal
with these issues (see email.Header).
convert defaults to False.
The type of encoding (base64 or quoted-printable) will be based on the header_encoding
attribute.
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| body_encode( |
s[, convert]) |
- Body-encode the string s.
If convert is True (the default), the string will be converted
from the input charset to output charset automatically. Unlike header_encode(),
there are no issues with byte boundaries and multibyte charsets in email bodies, so this
is usually pretty safe.
The type of encoding (base64 or quoted-printable) will be based on the body_encoding
attribute.
The Charset class also provides a number of methods to support
standard operations and built-in functions.
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- Returns input_charset as a string coerced to lower case. __repr__()
is an alias for __str__().
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- This method allows you to compare two Charset instances for
equality.
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- This method allows you to compare two Charset instances for
inequality.
The email.Charset module also provides the following functions for
adding new entries to the global character set, alias, and codec registries:
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| add_charset( |
charset[, header_enc[, body_enc[,
output_charset]]]) |
- Add character properties to the global registry.
charset is the input character set, and must be the canonical name of a
character set.
Optional header_enc and body_enc is either Charset.QP
for quoted-printable, Charset.BASE64 for base64 encoding, Charset.SHORTEST
for the shortest of quoted-printable or base64 encoding, or None for no
encoding. SHORTEST is only valid for header_enc. The default is None
for no encoding.
Optional output_charset is the character set that the output should be in.
Conversions will proceed from input charset, to Unicode, to the output charset when the
method Charset.convert() is called. The default is to output in
the same character set as the input.
Both input_charset and output_charset must have Unicode codec
entries in the module's character set-to-codec mapping; use add_codec()
to add codecs the module does not know about. See the codecs module's documentation for more information.
The global character set registry is kept in the module global dictionary CHARSETS.
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| add_alias( |
alias, canonical) |
- Add a character set alias. alias is the alias name, e.g.
latin-1.
canonical is the character set's canonical name, e.g. iso-8859-1.
The global charset alias registry is kept in the module global dictionary ALIASES.
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| add_codec( |
charset, codecname) |
- Add a codec that map characters in the given character set to and from Unicode.
charset is the canonical name of a character set. codecname is
the name of a Python codec, as appropriate for the second argument to the unicode() built-in, or to the encode()
method of a Unicode string.
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