email.parser
: 剖析 Email 消息
¶
Message object structures can be created in one of two ways: they can be created from whole cloth by instantiating
Message
objects and stringing them together via
attach()
and
set_payload()
calls, or they can be created by parsing a flat text representation of the email message.
The
email
package provides a standard parser that understands most email document structures, including MIME documents. You can pass the parser a string or a file object, and the parser will return to you the root
Message
实例的对象结构。对于简单非 MIME 消息，此根对象的负载可能是包含消息文本的字符串。对于 MIME 消息，根对象会返回
True
从其
is_multipart()
method, and the subparts can be accessed via the
get_payload()
and
walk()
方法。
There are actually two parser interfaces available for use, the classic
Parser
API 和增量
FeedParser
API. The classic
Parser
API is fine if you have the entire text of the message in memory as a string, or if the entire message lives in a file on the file system.
FeedParser
is more appropriate for when you’re reading the message from a stream which might block waiting for more input (e.g. reading an email message from a socket). The
FeedParser
can consume and parse the message incrementally, and only returns the root object when you close the parser
1
.
Note that the parser can be extended in limited ways, and of course you can implement your own parser completely from scratch. There is no magical connection between the
email
包的捆绑剖析器和
Message
class, so your custom parser can create message object trees any way it finds necessary.
2.4 版新增。
The
FeedParser
，导入从
email.feedparser
module, provides an API that is conducive to incremental parsing of email messages, such as would be necessary when reading the text of an email message from a source that can block (e.g. a socket). The
FeedParser
can of course be used to parse an email message fully contained in a string or a file, but the classic
Parser
API may be more convenient for such use cases. The semantics and results of the two parser APIs are identical.
The
FeedParser
’s API is simple; you create an instance, feed it a bunch of text until there’s no more to feed it, then close the parser to retrieve the root message object. The
FeedParser
is extremely accurate when parsing standards-compliant messages, and it does a very good job of parsing non-compliant messages, providing information about how a message was deemed broken. It will populate a message object’s
defects
attribute with a list of any problems it found in a message. See the
email.errors
module for the list of defects that it can find.
Here is the API for the
FeedParser
:
email.parser.
FeedParser
(
[
_factory
]
)
¶
创建
FeedParser
实例。可选
_factory
is a no-argument callable that will be called whenever a new message object is needed. It defaults to the
email.message.Message
类。
feed
(
data
)
¶
Feed the
FeedParser
some more data.
data
should be a string containing one or more lines. The lines can be partial and the
FeedParser
will stitch such partial lines together properly. The lines in the string can have any of the common three line endings, carriage return, newline, or carriage return and newline (they can even be mixed).
close
(
)
¶
Closing a
FeedParser
completes the parsing of all previously fed data, and returns the root message object. It is undefined what happens if you feed more data to a closed
FeedParser
.
The
Parser
类，导入自
email.parser
module, provides an API that can be used to parse a message when the complete contents of the message are available in a string or file. The
email.parser
module also provides a second class, called
HeaderParser
which can be used if you’re only interested in the headers of the message.
HeaderParser
can be much faster in these situations, since it does not attempt to parse the message body, instead setting the payload to the raw body as a string.
HeaderParser
has the same API as the
Parser
类。
email.parser.
Parser
(
[
_class
]
)
¶
The constructor for the
Parser
class takes an optional argument
_class
. This must be a callable factory (such as a function or a class), and it is used whenever a sub-message object needs to be created. It defaults to
Message
(见
email.message
). The factory will be called without arguments.
可选 strict flag is ignored.
Deprecated since version 2.4:
由于
Parser
class is a backward compatible API wrapper around the new-in-Python 2.4
FeedParser
,
all
parsing is effectively non-strict. You should simply stop passing a
strict
flag to the
Parser
构造函数。
Changed in version 2.2.2: The strict flag was added.
2.4 版改变： The strict flag was deprecated.
The other public
Parser
methods are:
parse
(
fp
[
,
headersonly
]
)
¶
Read all the data from the file-like object
fp
, parse the resulting text, and return the root message object.
fp
must support both the
readline()
和
read()
methods on file-like objects.
The text contained in fp must be formatted as a block of RFC 2822 style headers and header continuation lines, optionally preceded by an envelope header. The header block is terminated either by the end of the data or by a blank line. Following the header block is the body of the message (which may contain MIME-encoded subparts).
可选
headersonly
is a flag specifying whether to stop parsing after reading the headers or not. The default is
False
, meaning it parses the entire contents of the file.
Changed in version 2.2.2: The headersonly flag was added.
parsestr
(
text
[
,
headersonly
]
)
¶
类似于
parse()
method, except it takes a string object instead of a file-like object. Calling this method on a string is exactly equivalent to wrapping
text
在
StringIO
instance first and calling
parse()
.
可选
headersonly
is as with the
parse()
方法。
Changed in version 2.2.2: The headersonly flag was added.
Since creating a message object structure from a string or a file object is such a common task, two functions are provided as a convenience. They are available in the top-level
email
package namespace.
email.
message_from_string
(
s
[
,
_class
[
,
strict
]
]
)
¶
Return a message object structure from a string. This is exactly equivalent to
Parser().parsestr(s)
。可选
_class
and
strict
的解释就像
Parser
类构造函数。
Changed in version 2.2.2: The strict flag was added.
email.
message_from_file
(
fp
[
,
_class
[
,
strict
]
]
)
¶
Return a message object structure tree from an open file object. This is exactly equivalent to
Parser().parse(fp)
。可选
_class
and
strict
的解释就像
Parser
类构造函数。
Changed in version 2.2.2: The strict flag was added.
Here’s an example of how you might use this at an interactive Python prompt:
>>> import email >>> msg = email.message_from_string(myString)
这里是有关剖析语义的一些注意事项：
大多数非
multipart
type messages are parsed as a single message object with a string payload. These objects will return
False
for
is_multipart()
. Their
get_payload()
method will return a string object.
所有
multipart
type messages will be parsed as a container message object with a list of sub-message objects for their payload. The outer container message will return
True
for
is_multipart()
and their
get_payload()
method will return the list of
Message
subparts.
Most messages with a content type of
message/*
(如
message/delivery-status
and
message/rfc822
) will also be parsed as container object containing a list payload of length 1. Their
is_multipart()
method will return
True
. The single element in the list payload will be a sub-message object.
Some non-standards compliant messages may not be internally consistent about their
multipart
-edness. Such messages may have a
Content-Type
header of type
multipart
, but their
is_multipart()
method may return
False
. If such messages were parsed with the
FeedParser
, they will have an instance of the
MultipartInvariantViolationDefect
class in their
defects
attribute list. See
email.errors
了解细节。
脚注
As of email package version 3.0, introduced in Python 2.4, the classic
Parser
was re-implemented in terms of the
FeedParser
, so the semantics and results are identical between the two parsers.