email.message.Message
: Representing an email message using the
compat32
API
¶
Message
class is very similar to the
EmailMessage
class, without the methods added by that class, and with the default behavior of certain other methods being slightly different. We also document here some methods that, while supported by the
EmailMessage
class, are not recommended unless you are dealing with legacy code.
The philosophy and structure of the two classes is otherwise the same.
This document describes the behavior under the default (for
Message
) policy
Compat32
. If you are going to use another policy, you should be using the
EmailMessage
class instead.
An email message consists of headers 和 payload . Headers must be RFC 5233 style names and values, where the field name and value are separated by a colon. The colon is not part of either the field name or the field value. The payload may be a simple text message, or a binary object, or a structured sequence of sub-messages each with their own set of headers and their own payload. The latter type of payload is indicated by the message having a MIME type such as multipart/* or message/rfc822 .
The conceptual model provided by a
Message
object is that of an ordered dictionary of headers with additional methods for accessing both specialized information from the headers, for accessing the payload, for generating a serialized version of the message, and for recursively walking over the object tree. Note that duplicate headers are supported but special methods must be used to access them.
Message
pseudo-dictionary is indexed by the header names, which must be ASCII values. The values of the dictionary are strings that are supposed to contain only ASCII characters; there is some special handling for non-ASCII input, but it doesn’t always produce the correct results. Headers are stored and returned in case-preserving form, but field names are matched case-insensitively. There may also be a single envelope header, also known as the
Unix-From
header or the
From_
header. The
payload
is either a string or bytes, in the case of simple message objects, or a list of
Message
objects, for MIME container documents (e.g.
multipart/*
and
message/rfc822
).
Here are the methods of the
Message
类：
email.message.
Message
(
policy=compat32
)
¶
若
policy
is specified (it must be an instance of a
policy
class) use the rules it specifies to update and serialize the representation of the message. If
policy
is not set, use the
compat32
policy, which maintains backward compatibility with the Python 3.2 version of the email package. For more information see the
policy
文档编制。
3.3 版改变： policy 关键词自变量被添加。
as_string
(
unixfrom=False
,
maxheaderlen=0
,
policy=None
)
¶
Return the entire message flattened as a string. When optional
unixfrom
is true, the envelope header is included in the returned string.
unixfrom
默认为
False
. For backward compatibility reasons,
maxheaderlen
默认为
0
, so if you want a different value you must override it explicitly (the value specified for
max_line_length
in the policy will be ignored by this method). The
policy
argument may be used to override the default policy obtained from the message instance. This can be used to control some of the formatting produced by the method, since the specified
policy
will be passed to the
生成器
.
Flattening the message may trigger changes to the
Message
if defaults need to be filled in to complete the transformation to a string (for example, MIME boundaries may be generated or modified).
Note that this method is provided as a convenience and may not always format the message the way you want. For example, by default it does not do the mangling of lines that begin with
From
that is required by the unix mbox format. For more flexibility, instantiate a
生成器
instance and use its
flatten()
method directly. For example:
from io import StringIO
from email.generator import Generator
fp = StringIO()
g = Generator(fp, mangle_from_=True, maxheaderlen=60)
g.flatten(msg)
text = fp.getvalue()
If the message object contains binary data that is not encoded according to RFC standards, the non-compliant data will be replaced by unicode “unknown character” code points. (See also
as_bytes()
and
BytesGenerator
.)
3.4 版改变： the policy 关键词自变量被添加。
__str__
(
)
¶
相当于
as_string()
. Allows
str(msg)
to produce a string containing the formatted message.
as_bytes
(
unixfrom=False
,
policy=None
)
¶
Return the entire message flattened as a bytes object. When optional
unixfrom
is true, the envelope header is included in the returned string.
unixfrom
默认为
False
。
policy
argument may be used to override the default policy obtained from the message instance. This can be used to control some of the formatting produced by the method, since the specified
policy
will be passed to the
BytesGenerator
.
Flattening the message may trigger changes to the
Message
if defaults need to be filled in to complete the transformation to a string (for example, MIME boundaries may be generated or modified).
Note that this method is provided as a convenience and may not always format the message the way you want. For example, by default it does not do the mangling of lines that begin with
From
that is required by the unix mbox format. For more flexibility, instantiate a
BytesGenerator
instance and use its
flatten()
method directly. For example:
from io import BytesIO
from email.generator import BytesGenerator
fp = BytesIO()
g = BytesGenerator(fp, mangle_from_=True, maxheaderlen=60)
g.flatten(msg)
text = fp.getvalue()
3.4 版新增。
__bytes__
(
)
¶
相当于
as_bytes()
. Allows
bytes(msg)
to produce a bytes object containing the formatted message.
3.4 版新增。
is_multipart
(
)
¶
返回
True
if the message’s payload is a list of sub-
Message
objects, otherwise return
False
。当
is_multipart()
返回
False
, the payload should be a string object (which might be a CTE encoded binary payload). (Note that
is_multipart()
returning
True
does not necessarily mean that “msg.get_content_maintype() == ‘multipart’” will return the
True
。例如，
is_multipart
will return
True
when the
Message
是类型
message/rfc822
.)
set_unixfrom
(
unixfrom
)
¶
Set the message’s envelope header to unixfrom , which should be a string.
get_unixfrom
(
)
¶
Return the message’s envelope header. Defaults to
None
if the envelope header was never set.
attach
(
payload
)
¶
Add the given
payload
to the current payload, which must be
None
or a list of
Message
objects before the call. After the call, the payload will always be a list of
Message
objects. If you want to set the payload to a scalar object (e.g. a string), use
set_payload()
代替。
This is a legacy method. On the
EmailMessage
class its functionality is replaced by
set_content()
and the related
make
and
add
方法。
get_payload
(
i=None
,
decode=False
)
¶
Return the current payload, which will be a list of
Message
objects when
is_multipart()
is
True
, or a string when
is_multipart()
is
False
. If the payload is a list and you mutate the list object, you modify the message’s payload in place.
With optional argument
i
,
get_payload()
will return the
i
-th element of the payload, counting from zero, if
is_multipart()
is
True
. An
IndexError
会被引发若
i
is less than 0 or greater than or equal to the number of items in the payload. If the payload is a string (i.e.
is_multipart()
is
False
) 和
i
is given, a
TypeError
被引发。
可选
decode
is a flag indicating whether the payload should be decoded or not, according to the
Content-Transfer-Encoding
header. When
True
and the message is not a multipart, the payload will be decoded if this header’s value is
quoted-printable
or
base64
. If some other encoding is used, or
Content-Transfer-Encoding
header is missing, the payload is returned as-is (undecoded). In all cases the returned value is binary data. If the message is a multipart and the
decode
flag is
True
, then
None
is returned. If the payload is base64 and it was not perfectly formed (missing padding, characters outside the base64 alphabet), then an appropriate defect will be added to the message’s defect property (
InvalidBase64PaddingDefect
or
InvalidBase64CharactersDefect
, respectively).
当
decode
is
False
(the default) the body is returned as a string without decoding the
Content-Transfer-Encoding
. However, for a
Content-Transfer-Encoding
of 8bit, an attempt is made to decode the original bytes using the
charset
specified by the
Content-Type
header, using the
replace
error handler. If no
charset
is specified, or if the
charset
given is not recognized by the email package, the body is decoded using the default ASCII charset.
This is a legacy method. On the
EmailMessage
class its functionality is replaced by
get_content()
and
iter_parts()
.
set_payload
(
payload
,
charset=None
)
¶
Set the entire message object’s payload to
payload
. It is the client’s responsibility to ensure the payload invariants. Optional
charset
sets the message’s default character set; see
set_charset()
了解细节。
This is a legacy method. On the
EmailMessage
class its functionality is replaced by
set_content()
.
set_charset
(
charset
)
¶
Set the character set of the payload to
charset
, which can either be a
Charset
实例 (见
email.charset
), a string naming a character set, or
None
. If it is a string, it will be converted to a
Charset
instance. If
charset
is
None
，
charset
parameter will be removed from the
Content-Type
header (the message will not be otherwise modified). Anything else will generate a
TypeError
.
If there is no existing
MIME-Version
header one will be added. If there is no existing
Content-Type
header, one will be added with a value of
text/plain
. Whether the
Content-Type
header already exists or not, its
charset
parameter will be set to
charset.output_charset
。若
charset.input_charset
and
charset.output_charset
differ, the payload will be re-encoded to the
output_charset
. If there is no existing
Content-Transfer-Encoding
header, then the payload will be transfer-encoded, if needed, using the specified
Charset
, and a header with the appropriate value will be added. If a
Content-Transfer-Encoding
header already exists, the payload is assumed to already be correctly encoded using that
Content-Transfer-Encoding
and is not modified.
This is a legacy method. On the
EmailMessage
class its functionality is replaced by the
charset
parameter of the
email.emailmessage.EmailMessage.set_content()
方法。
get_charset
(
)
¶
返回
Charset
instance associated with the message’s payload.
This is a legacy method. On the
EmailMessage
class it always returns
None
.
The following methods implement a mapping-like interface for accessing the message’s
RFC 2822
headers. Note that there are some semantic differences between these methods and a normal mapping (i.e. dictionary) interface. For example, in a dictionary there are no duplicate keys, but here there may be duplicate message headers. Also, in dictionaries there is no guaranteed order to the keys returned by
keys()
, but in a
Message
object, headers are always returned in the order they appeared in the original message, or were added to the message later. Any header deleted and then re-added are always appended to the end of the header list.
These semantic differences are intentional and are biased toward maximal convenience.
Note that in all cases, any envelope header present in the message is not included in the mapping interface.
In a model generated from bytes, any header values that (in contravention of the RFCs) contain non-ASCII bytes will, when retrieved through this interface, be represented as
Header
objects with a charset of
unknown-8bit
.
__len__
(
)
¶
Return the total number of headers, including duplicates.
__contains__
(
name
)
¶
Return true if the message object has a field named
name
. Matching is done case-insensitively and
name
should not include the trailing colon. Used for the
in
operator, e.g.:
if 'message-id' in myMessage:
print('Message-ID:', myMessage['message-id'])
__getitem__
(
name
)
¶
Return the value of the named header field.
name
should not include the colon field separator. If the header is missing,
None
is returned; a
KeyError
is never raised.
Note that if the named field appears more than once in the message’s headers, exactly which of those field values will be returned is undefined. Use the
get_all()
method to get the values of all the extant named headers.
__setitem__
(
name
,
val
)
¶
Add a header to the message with field name name and value val . The field is appended to the end of the message’s existing fields.
Note that this does not overwrite or delete any existing header with the same name. If you want to ensure that the new header is the only one present in the message with field name name , delete the field first, e.g.:
del msg['subject']
msg['subject'] = 'Python roolz!'
__delitem__
(
name
)
¶
Delete all occurrences of the field with name name from the message’s headers. No exception is raised if the named field isn’t present in the headers.
keys
(
)
¶
Return a list of all the message’s header field names.
values
(
)
¶
Return a list of all the message’s field values.
items
(
)
¶
Return a list of 2-tuples containing all the message’s field headers and values.
get
(
name
,
failobj=None
)
¶
Return the value of the named header field. This is identical to
__getitem__()
except that optional
failobj
is returned if the named header is missing (defaults to
None
).
Here are some additional useful methods:
get_all
(
name
,
failobj=None
)
¶
Return a list of all the values for the field named
name
. If there are no such named headers in the message,
failobj
is returned (defaults to
None
).
add_header
(
_name
,
_value
,
**_params
)
¶
Extended header setting. This method is similar to
__setitem__()
except that additional header parameters can be provided as keyword arguments.
_name
is the header field to add and
_value
是
primary
value for the header.
For each item in the keyword argument dictionary
_params
, the key is taken as the parameter name, with underscores converted to dashes (since dashes are illegal in Python identifiers). Normally, the parameter will be added as
key="value"
unless the value is
None
, in which case only the key will be added. If the value contains non-ASCII characters, it can be specified as a three tuple in the format
(CHARSET,
LANGUAGE,
VALUE)
，其中
CHARSET
is a string naming the charset to be used to encode the value,
LANGUAGE
can usually be set to
None
or the empty string (see
RFC 2231
for other possibilities), and
VALUE
is the string value containing non-ASCII code points. If a three tuple is not passed and the value contains non-ASCII characters, it is automatically encoded in
RFC 2231
format using a
CHARSET
of
utf-8
和
LANGUAGE
of
None
.
Here’s an example:
msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')
This will add a header that looks like
Content-Disposition: attachment; filename="bud.gif"
An example with non-ASCII characters:
msg.add_header('Content-Disposition', 'attachment',
filename=('iso-8859-1', '', 'Fußballer.ppt'))
Which produces
Content-Disposition: attachment; filename*="iso-8859-1''Fu%DFballer.ppt"
replace_header
(
_name
,
_value
)
¶
Replace a header. Replace the first header found in the message that matches
_name
, retaining header order and field name case. If no matching header was found, a
KeyError
被引发。
get_content_type
(
)
¶
Return the message’s content type. The returned string is coerced to lower case of the form
maintype/subtype
. If there was no
Content-Type
header in the message the default type as given by
get_default_type()
will be returned. Since according to
RFC 2045
, messages always have a default type,
get_content_type()
will always return a value.
RFC 2045 defines a message’s default type to be text/plain unless it appears inside a multipart/digest container, in which case it would be message/rfc822 。若 Content-Type header has an invalid type specification, RFC 2045 mandates that the default type be text/plain .
get_content_maintype
(
)
¶
Return the message’s main content type. This is the
maintype
part of the string returned by
get_content_type()
.
get_content_subtype
(
)
¶
Return the message’s sub-content type. This is the
subtype
part of the string returned by
get_content_type()
.
get_default_type
(
)
¶
Return the default content type. Most messages have a default content type of text/plain , except for messages that are subparts of multipart/digest containers. Such subparts have a default content type of message/rfc822 .
set_default_type
(
ctype
)
¶
Set the default content type. ctype should either be text/plain or message/rfc822 , although this is not enforced. The default content type is not stored in the Content-Type header.
get_params
(
failobj=None
,
header='content-type'
,
unquote=True
)
¶
Return the message’s
Content-Type
parameters, as a list. The elements of the returned list are 2-tuples of key/value pairs, as split on the
'='
sign. The left hand side of the
'='
is the key, while the right hand side is the value. If there is no
'='
sign in the parameter the value is the empty string, otherwise the value is as described in
get_param()
and is unquoted if optional
unquote
is
True
(the default).
可选 failobj is the object to return if there is no Content-Type header. Optional header is the header to search instead of Content-Type .
This is a legacy method. On the
EmailMessage
class its functionality is replaced by the
params
property of the individual header objects returned by the header access methods.
get_param
(
param
,
failobj=None
,
header='content-type'
,
unquote=True
)
¶
Return the value of the
Content-Type
header’s parameter
param
as a string. If the message has no
Content-Type
header or if there is no such parameter, then
failobj
is returned (defaults to
None
).
可选 header if given, specifies the message header to use instead of Content-Type .
Parameter keys are always compared case insensitively. The return value can either be a string, or a 3-tuple if the parameter was
RFC 2231
encoded. When it’s a 3-tuple, the elements of the value are of the form
(CHARSET,
LANGUAGE,
VALUE)
. Note that both
CHARSET
and
LANGUAGE
可以是
None
, in which case you should consider
VALUE
to be encoded in the
us-ascii
charset. You can usually ignore
LANGUAGE
.
If your application doesn’t care whether the parameter was encoded as in
RFC 2231
, you can collapse the parameter value by calling
email.utils.collapse_rfc2231_value()
, passing in the return value from
get_param()
. This will return a suitably decoded Unicode string when the value is a tuple, or the original string unquoted if it isn’t. For example:
rawparam = msg.get_param('foo')
param = email.utils.collapse_rfc2231_value(rawparam)
In any case, the parameter value (either the returned string, or the
VALUE
item in the 3-tuple) is always unquoted, unless
unquote
被设为
False
.
This is a legacy method. On the
EmailMessage
class its functionality is replaced by the
params
property of the individual header objects returned by the header access methods.
set_param
(
param
,
value
,
header='Content-Type'
,
requote=True
,
charset=None
,
language=''
,
replace=False
)
¶
Set a parameter in the Content-Type header. If the parameter already exists in the header, its value will be replaced with value 。若 Content-Type header as not yet been defined for this message, it will be set to text/plain and the new parameter value will be appended as per RFC 2045 .
可选
header
specifies an alternative header to
Content-Type
, and all parameters will be quoted as necessary unless optional
requote
is
False
(the default is
True
).
If optional charset is specified, the parameter will be encoded according to RFC 2231 . Optional language specifies the RFC 2231 language, defaulting to the empty string. Both charset and language should be strings.
若
replace
is
False
(the default) the header is moved to the end of the list of headers. If
replace
is
True
, the header will be updated in place.
3.4 版改变：
replace
keyword was added.
del_param
(
param
,
header='content-type'
,
requote=True
)
¶
Remove the given parameter completely from the
Content-Type
header. The header will be re-written in place without the parameter or its value. All values will be quoted as necessary unless
requote
is
False
(the default is
True
). Optional
header
specifies an alternative to
Content-Type
.
set_type
(
type
,
header='Content-Type'
,
requote=True
)
¶
Set the main type and subtype for the
Content-Type
header.
type
must be a string in the form
maintype/subtype
, otherwise a
ValueError
被引发。
This method replaces the
Content-Type
header, keeping all the parameters in place. If
requote
is
False
, this leaves the existing header’s quoting as is, otherwise the parameters will be quoted (the default).
An alternative header can be specified in the header argument. When the Content-Type header is set a MIME-Version header is also added.
This is a legacy method. On the
EmailMessage
class its functionality is replaced by the
make_
and
add_
方法。
get_filename
(
failobj=None
)
¶
Return the value of the
filename
parameter of the
Content-Disposition
header of the message. If the header does not have a
filename
parameter, this method falls back to looking for the
name
parameter on the
Content-Type
header. If neither is found, or the header is missing, then
failobj
is returned. The returned string will always be unquoted as per
email.utils.unquote()
.
get_boundary
(
failobj=None
)
¶
Return the value of the
boundary
parameter of the
Content-Type
header of the message, or
failobj
if either the header is missing, or has no
boundary
parameter. The returned string will always be unquoted as per
email.utils.unquote()
.
set_boundary
(
boundary
)
¶
设置
boundary
parameter of the
Content-Type
header to
boundary
.
set_boundary()
will always quote
boundary
if necessary. A
HeaderParseError
is raised if the message object has no
Content-Type
header.
Note that using this method is subtly different than deleting the old
Content-Type
header and adding a new one with the new boundary via
add_header()
, because
set_boundary()
preserves the order of the
Content-Type
header in the list of headers. However, it does
not
preserve any continuation lines which may have been present in the original
Content-Type
header.
get_content_charset
(
failobj=None
)
¶
返回
charset
parameter of the
Content-Type
header, coerced to lower case. If there is no
Content-Type
header, or if that header has no
charset
参数，
failobj
被返回。
Note that this method differs from
get_charset()
which returns the
Charset
instance for the default encoding of the message body.
get_charsets
(
failobj=None
)
¶
Return a list containing the character set names in the message. If the message is a multipart , then the list will contain one element for each subpart in the payload, otherwise, it will be a list of length 1.
Each item in the list will be a string which is the value of the
charset
parameter in the
Content-Type
header for the represented subpart. However, if the subpart has no
Content-Type
header, no
charset
parameter, or is not of the
text
main MIME type, then that item in the returned list will be
failobj
.
get_content_disposition
(
)
¶
Return the lowercased value (without parameters) of the message’s
Content-Disposition
header if it has one, or
None
. The possible values for this method are
inline
,
attachment
or
None
if the message follows
RFC 2183
.
3.5 版新增。
walk
(
)
¶
walk()
method is an all-purpose generator which can be used to iterate over all the parts and subparts of a message object tree, in depth-first traversal order. You will typically use
walk()
as the iterator in a
for
loop; each iteration returns the next subpart.
Here’s an example that prints the MIME type of every part of a multipart message structure:
>>> for part in msg.walk():
... print(part.get_content_type())
multipart/report
text/plain
message/delivery-status
text/plain
text/plain
message/rfc822
text/plain
walk
iterates over the subparts of any part where
is_multipart()
返回
True
, even though
msg.get_content_maintype()
==
'multipart'
may return
False
. We can see this in our example by making use of the
_structure
debug helper function:
>>> for part in msg.walk():
... print(part.get_content_maintype() == 'multipart'),
... part.is_multipart())
True True
False False
False True
False False
False False
False True
False False
>>> _structure(msg)
multipart/report
text/plain
message/delivery-status
text/plain
text/plain
message/rfc822
text/plain
Here the
message
parts are not
multiparts
, but they do contain subparts.
is_multipart()
返回
True
and
walk
descends into the subparts.
Message
objects can also optionally contain two instance attributes, which can be used when generating the plain text of a MIME message.
preamble
¶
The format of a MIME document allows for some text between the blank line following the headers, and the first multipart boundary string. Normally, this text is never visible in a MIME-aware mail reader because it falls outside the standard MIME armor. However, when viewing the raw text of the message, or when viewing the message in a non-MIME aware reader, this text can become visible.
preamble
attribute contains this leading extra-armor text for MIME documents. When the
Parser
discovers some text after the headers but before the first boundary string, it assigns this text to the message’s
preamble
attribute. When the
生成器
is writing out the plain text representation of a MIME message, and it finds the message has a
preamble
attribute, it will write this text in the area between the headers and the first boundary. See
email.parser
and
email.generator
了解细节。
Note that if the message object has no preamble, the
preamble
属性将是
None
.
epilogue
¶
epilogue attribute acts the same way as the preamble attribute, except that it contains text that appears between the last boundary and the end of the message.
You do not need to set the epilogue to the empty string in order for the
生成器
to print a newline at the end of the file.
defects
¶
defects
attribute contains a list of all the problems found when parsing this message. See
email.errors
for a detailed description of the possible parsing defects.