email
— Email 和 MIME 处理包
»
email.policy
：策略对象
¶
3.3 版新增。
The
email
package’s prime focus is the handling of email messages as described by the various email and MIME RFCs. However, the general format of email messages (a block of header fields each consisting of a name followed by a colon followed by a value, the whole block followed by a blank line and an arbitrary ‘body’), is a format that has found utility outside of the realm of email. Some of these uses conform fairly closely to the main RFCs, some do not. And even when working with email, there are times when it is desirable to break strict compliance with the RFCs.
策略对象赋予 email 包灵活处理所有这些迥然不同的用例。
A
Policy
对象封装了一组属性和方法，用于控制 email 包在使用期间各个组件的行为。
Policy
实例可以将各种类和方法传入 email 包以改变其默认行为。可设置的值及其默认值的描述见下文。
There is a default policy used by all classes in the email package. This policy is named
Compat32
, with a corresponding pre-defined instance named
compat32
. It provides for complete backward compatibility (in some cases, including bug compatibility) with the pre-Python3.3 version of the email package.
The first part of this documentation covers the features of
Policy
，
抽象基类
that defines the features that are common to all policy objects, including
compat32
. This includes certain hook methods that are called internally by the email package, which a custom policy could override to obtain different behavior.
当
Message
object is created, it acquires a policy. By default this will be
compat32
, but a different policy can be specified. If the
Message
is created by a
parser
, a policy passed to the parser will be the policy used by the
Message
it creates. If the
Message
is created by the program, then the policy can be specified when it is created. When a
Message
is passed to a
generator
, the generator uses the policy from the
Message
by default, but you can also pass a specific policy to the generator that will override the one stored on the
Message
对象。
Policy
instances are immutable, but they can be cloned, accepting the same keyword arguments as the class constructor and returning a new
Policy
instance that is a copy of the original but with the specified attributes values changed.
As an example, the following code could be used to read an email message from a file on disk and pass it to the system
sendmail
程序在 Unix 系统：
>>> from email import message_from_binary_file >>> from email.generator import BytesGenerator >>> from email import policy >>> from subprocess import Popen, PIPE >>> with open('mymsg.txt', 'rb') as f: ... msg = message_from_binary_file(f, policy=policy.default) >>> p = Popen(['sendmail', msg['To'].addresses[0]], stdin=PIPE) >>> g = BytesGenerator(p.stdin, policy=msg.policy.clone(linesep='\r\n')) >>> g.flatten(msg) >>> p.stdin.close() >>> rc = p.wait()
Here we are telling
BytesGenerator
to use the RFC correct line separator characters when creating the binary string to feed into
sendmail's
stdin
, where the default policy would use
\n
line separators.
Some email package methods accept a
policy
keyword argument, allowing the policy to be overridden for that method. For example, the following code uses the
as_bytes()
方法在
msg
object from the previous example and writes the message to a file using the native line separators for the platform on which it is running:
>>> import os >>> with open('converted.txt', 'wb') as f: ... f.write(msg.as_bytes(policy=msg.policy.clone(linesep=os.linesep))) 17
Policy objects can also be combined using the addition operator, producing a policy object whose settings are a combination of the non-default values of the summed objects:
>>> compat_SMTP = policy.compat32.clone(linesep='\r\n') >>> compat_strict = policy.compat32.clone(raise_on_defect=True) >>> compat_strict_SMTP = compat_SMTP + compat_strict
This operation is not commutative; that is, the order in which the objects are added matters. To illustrate:
>>> policy100 = policy.compat32.clone(max_line_length=100) >>> policy80 = policy.compat32.clone(max_line_length=80) >>> apolicy = policy100 + policy80 >>> apolicy.max_line_length 80 >>> apolicy = policy80 + policy100 >>> apolicy.max_line_length 100
email.policy.
Policy
(
**kw
)
¶
这是
抽象基类
for all policy classes. It provides default implementations for a couple of trivial methods, as well as the implementation of the immutability property, the
clone()
方法，和构造函数语义。
The constructor of a policy class can be passed various keyword arguments. The arguments that may be specified are any non-method properties on this class, plus any additional non-method properties on the concrete class. A value specified in the constructor will override the default value for the corresponding attribute.
This class defines the following properties, and thus values for the following may be passed in the constructor of any policy class:
max_line_length
¶
The maximum length of any line in the serialized output, not counting the end of line character(s). Default is 78, per
RFC 5322
。值为
0
or
None
indicates that no line wrapping should be done at all.
linesep
¶
The string to be used to terminate lines in serialized output. The default is
\n
because that’s the internal end-of-line discipline used by Python, though
\r\n
is required by the RFCs.
cte_type
¶
Controls the type of Content Transfer Encodings that may be or are required to be used. The possible values are:
7bit
|
all data must be “7 bit clean” (ASCII-only). This means that where necessary data will be encoded using either quoted-printable or base64 encoding. |
8bit
|
data is not constrained to be 7 bit clean. Data in headers is
still required to be ASCII-only and so will be encoded (see
‘binary_fold’ below for an exception), but body parts may use
the
8bit
CTE.
|
A
cte_type
value of
8bit
only works with
BytesGenerator
, not
Generator
, because strings cannot contain binary data. If a
Generator
is operating under a policy that specifies
cte_type=8bit
, it will act as if
cte_type
is
7bit
.
raise_on_defect
¶
若
True
, any defects encountered will be raised as errors. If
False
(the default), defects will be passed to the
register_defect()
方法。
下列
Policy
method is intended to be called by code using the email library to create policy instances with custom settings:
clone
(
**kw
)
¶
返回新的
Policy
instance whose attributes have the same values as the current instance, except where those attributes are given new values by the keyword arguments.
The remaining
Policy
methods are called by the email package code, and are not intended to be called by an application using the email package. A custom policy must implement all of these methods.
handle_defect
(
obj
,
defect
)
¶
处理
defect
found on
obj
. When the email package calls this method,
defect
will always be a subclass of
Defect
.
默认实现校验
raise_on_defect
标志。若它是
True
,
defect
被引发作为异常。若它是
False
(默认)，
obj
and
defect
被传递给
register_defect()
.
register_defect
(
obj
,
defect
)
¶
注册
defect
on
obj
. In the email package,
defect
will always be a subclass of
Defect
.
默认实现调用
append
方法在
defects
attribute of
obj
. When the email package calls
handle_defect
,
obj
will normally have a
defects
attribute that has an
append
method. Custom object types used with the email package (for example, custom
Message
objects) should also provide such an attribute, otherwise defects in parsed messages will raise unexpected errors.
header_max_count
(
name
)
¶
Return the maximum allowed number of headers named name .
Called when a header is added to a
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
ValueError
被引发。
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.)
默认实现返回
None
对于所有头名称。
header_source_parse
(
sourcelines
)
¶
The email package calls this method with a list of strings, each string ending with the line separation characters found in the source being parsed. The first line includes the field header name and separator. All whitespace in the source is preserved. The method should return the
(name, value)
tuple that is to be stored in the
Message
to represent the parsed header.
If an implementation wishes to retain compatibility with the existing email package policies,
name
should be the case preserved name (all characters up to the ‘
:
‘ separator), while
value
should be the unfolded value (all line separator characters removed, but whitespace kept intact), stripped of leading whitespace.
sourcelines 可能包含替代转义二进制数据。
没有默认实现
header_store_parse
(
name
,
value
)
¶
The email package calls this method with the name and value provided by the application program when the application program is modifying a
Message
programmatically (as opposed to a
Message
created by a parser). The method should return the
(name, value)
tuple that is to be stored in the
Message
to represent the header.
If an implementation wishes to retain compatibility with the existing email package policies, the name and value should be strings or string subclasses that do not change the content of the passed in arguments.
没有默认实现
header_fetch_parse
(
name
,
value
)
¶
The email package calls this method with the
name
and
value
currently stored in the
Message
when that header is requested by the application program, and whatever the method returns is what is passed back to the application as the value of the header being retrieved. Note that there may be more than one header with the same name stored in the
Message
; the method is passed the specific name and value of the header destined to be returned to the application.
value may contain surrogateescaped binary data. There should be no surrogateescaped binary data in the value returned by the method.
没有默认实现
fold
(
name
,
value
)
¶
The email package calls this method with the
name
and
value
currently stored in the
Message
for a given header. The method should return a string that represents that header “folded” correctly (according to the policy settings) by composing the
name
采用
value
and inserting
linesep
characters at the appropriate places. See
RFC 5322
for a discussion of the rules for folding email headers.
value may contain surrogateescaped binary data. There should be no surrogateescaped binary data in the string returned by the method.
fold_binary
(
name
,
value
)
¶
如同
fold()
, except that the returned value should be a bytes object rather than a string.
value 可能包含替代转义二进制数据。可以将这些转换回二进制数据，当返回字节对象时。
email.policy.
Compat32
(
**kw
)
¶
此具体
Policy
is the backward compatibility policy. It replicates the behavior of the email package in Python 3.2. The
policy
module also defines an instance of this class,
compat32
, that is used as the default policy. Thus the default behavior of the email package is to maintain compatibility with Python 3.2.
类提供以下具体抽象方法实现对于
Policy
:
header_source_parse
(
sourcelines
)
¶
The name is parsed as everything up to the ‘
:
‘ and returned unmodified. The value is determined by stripping leading whitespace off the remainder of the first line, joining all subsequent lines together, and stripping any trailing carriage return or linefeed characters.
header_store_parse
(
name
,
value
)
¶
不修改返回名称和值。
fold
(
name
,
value
)
¶
Headers are folded using the
Header
folding algorithm, which preserves existing line breaks in the value, and wraps each resulting line to the
max_line_length
. Non-ASCII binary data are CTE encoded using the
unknown-8bit
字符集。
fold_binary
(
name
,
value
)
¶
Headers are folded using the
Header
folding algorithm, which preserves existing line breaks in the value, and wraps each resulting line to the
max_line_length
。若
cte_type
is
7bit
, non-ascii binary data is CTE encoded using the
unknown-8bit
charset. Otherwise the original source header is used, with its existing line breaks and any (RFC invalid) binary data it may contain.
注意
The documentation below describes new policies that are included in the standard library on a provisional basis . Backwards incompatible changes (up to and including removal of the feature) may occur if deemed necessary by the core developers.
email.policy.
EmailPolicy
(
**kw
)
¶
此具体
Policy
provides behavior that is intended to be fully compliant with the current email RFCs. These include (but are not limited to)
RFC 5322
,
RFC 2047
, and the current MIME RFCs.
This policy adds new header parsing and folding algorithms. Instead of simple strings, headers are
str
subclasses with attributes that depend on the type of the field. The parsing and folding algorithm fully implement
RFC 2047
and
RFC 5322
.
In addition to the settable attributes listed above that apply to all policies, this policy adds the following additional attributes:
refold_source
¶
If the value for a header in the
Message
object originated from a
parser
(as opposed to being set by a program), this attribute indicates whether or not a generator should refold that value when transforming the message back into stream form. The possible values are:
none
|
所有源值使用原始折叠 |
long
|
source values that have any line that is longer than
max_line_length
will be refolded
|
all
|
所有值被重新折叠。 |
默认为
long
.
header_factory
¶
可调用接受 2 自变量，
name
and
value
，其中
name
是头字段名称和
value
是展开头的字段值，并返回表示该头的字符串子类。默认
header_factory
(见
headerregistry
) is provided that understands some of the
RFC 5322
header field types. (Currently address fields and date fields have special treatment, while all other fields are treated as unstructured. This list will be completed before the extension is marked stable.)
content_manager
¶
An object with at least two methods: get_content and set_content. When the
get_content()
or
set_content()
方法对于
Message
object is called, it calls the corresponding method of this object, passing it the message object as its first argument, and any arguments or keywords that were passed to it as additional arguments. By default
content_manager
被设为
raw_data_manager
.
3.4 版新增。
类提供以下具体抽象方法实现对于
Policy
:
header_max_count
(
name
)
¶
返回值为
max_count
attribute of the specialized class used to represent the header with the given name.
header_source_parse
(
sourcelines
)
¶
The implementation of this method is the same as that for the
Compat32
policy.
header_store_parse
(
name
,
value
)
¶
The name is returned unchanged. If the input value has a
name
attribute and it matches
name
ignoring case, the value is returned unchanged. Otherwise the
name
and
value
被传递给
header_factory
, and the resulting header object is returned as the value. In this case a
ValueError
is raised if the input value contains CR or LF characters.
header_fetch_parse
(
name
,
value
)
¶
若值拥有
name
attribute, it is returned to unmodified. Otherwise the
name
，和
value
with any CR or LF characters removed, are passed to the
header_factory
, and the resulting header object is returned. Any surrogateescaped bytes get turned into the unicode unknown-character glyph.
fold
(
name
,
value
)
¶
Header folding is controlled by the
refold_source
policy setting. A value is considered to be a ‘source value’ if and only if it does not have a
name
attribute (having a
name
attribute means it is a header object of some sort). If a source value needs to be refolded according to the policy, it is converted into a header object by passing the
name
和
value
with any CR and LF characters removed to the
header_factory
. Folding of a header object is done by calling its
fold
method with the current policy.
Source values are split into lines using
splitlines()
. If the value is not to be refolded, the lines are rejoined using the
linesep
from the policy and returned. The exception is lines containing non-ascii binary data. In that case the value is refolded regardless of the
refold_source
setting, which causes the binary data to be CTE encoded using the
unknown-8bit
字符集。
fold_binary
(
name
,
value
)
¶
如同
fold()
if
cte_type
is
7bit
, except that the returned value is bytes.
若
cte_type
is
8bit
, non-ASCII binary data is converted back into bytes. Headers with binary data are not refolded, regardless of the
refold_header
setting, since there is no way to know whether the binary data consists of single byte characters or multibyte characters.
The following instances of
EmailPolicy
provide defaults suitable for specific application domains. Note that in the future the behavior of these instances (in particular the
HTTP
instance) may be adjusted to conform even more closely to the RFCs relevant to their domains.
email.policy.
default
¶
实例化的
EmailPolicy
采用所有不变默认值。此策略使用标准 Python
\n
行结束而不是 RFC 正确
\r\n
.
email.policy.
SMTP
¶
Suitable for serializing messages in conformance with the email RFCs. Like
default
, but with
linesep
设为
\r\n
, which is RFC compliant.
email.policy.
HTTP
¶
Suitable for serializing headers with for use in HTTP traffic. Like
SMTP
除了
max_line_length
被设为
None
(unlimited).
email.policy.
strict
¶
方便实例。如同
default
除了
raise_on_defect
被设为
True
. This allows any policy to be made strict by writing:
somepolicy + policy.strict
With all of these
EmailPolicies
, the effective API of the email package is changed from the Python 3.2 API in the following ways:
Message
results in that
header being parsed and a header object created.
Message
结果
in that header being parsed and a header object created and
被返回。
From the application view, this means that any header obtained through the
Message
is a header object with extra attributes, whose string value is the fully decoded unicode value of the header. Likewise, a header may be assigned a new value, or a new header created, using a unicode string, and the policy will take care of converting the unicode string into the correct RFC encoded form.
The header objects and their attributes are described in
headerregistry
.