Python的poplib.POP3和poplib.POP3_SSL包装器

Question

我不时地使用Python的poplib模块来检查/操作POP3邮箱，通常是交互的。然而，我发现接口非常麻烦，所以我决定尝试制作一个更容易使用的包装器。我没有试图使它完成，而是它基本上只是做我需要它做的。

我对此很满意(尽管建设性的批评总是受欢迎的)，但有一件事让我觉得有点奇怪。我没有多少写上下文经理的经验。我认为让Pop3类本身成为上下文管理器通常要简单得多，但是我创建了两个上下文管理器，而不是Pop3类，因为这允许我用最少的重复代码处理连接的代码。也许还有更好的方法？

import email
import email.utils
import poplib
from collections import OrderedDict
from functools import lru_cache

"""
Wrapper around poplib.POP3/poplib.POP3_SSL to make it easier to use. Doesn't (currently)
offer all functionality of poplib, but it does what I need it to.

Best used via the context manager connect() or connect_ssl():

    with pop3.connect_ssl(host, username, password) as p:
        for msg in p.messages.values():   # messages is a mapping: `num` -> `message`
            print(msg.summary)
            print('   to:', msg.headers['To'])
"""

class Message:
    """Message represents a message on a POP3 server"""

    def __init__(self, pop3, num, size):
        """Initialize a new instance. Don't call this manually: this is only
        meant to be called by Pop3 instances."""
        self.pop3 = pop3
        self.num = num
        self.size = size
        self.marked_for_deletion = False

    def __repr__(self):
        return 'Message(num=%d, size=%d)' % (self.num, self.size)

    def __str__(self):
        return self.summary

    @property
    @lru_cache()
    def headers(self):
        """The message's headers as an email.message instance"""
        return self.pop3._top(self.num, 0)

    @property
    @lru_cache()
    def email(self):
        """The complete email as an email.message instance"""
        return self.pop3._retr(self.num)

    @property
    def summary(self):
        """Summary line: deletion flag, message number, from, date, subject"""
        return '%s%-3d %-20s %-25s %s' % (
            '*' if self.marked_for_deletion else ' ',
            self.num,
            self.headers['From'],
            email.utils.parsedate_to_datetime(self.headers['Date']).isoformat(sep=' '),
            self.headers['Subject'],
            )

    def mark_for_deletion(self):
        """Mark this message for deletion. The server will delete the message
        when the connection is closed."""
        self.pop3._mark_for_deletion(self.num)

class Pop3:
    """Connection to a POP3 mailbox (simple wrapper around poplib.POP3 or poplib.POP3_SSL)

    Attribute `messages` holds the messages in the mailbox, as follows:
    Messages are represented by Message instances. Each message has an attribute num which
    is used to uniquely identify the message when communication with the server. 
    `messages` is an OrderedDict indexed on `num`.
    Use e.g. `messages.values()` to get all messages.
    """

    def __init__(self, poplib_pop3, username, password):
        """Initialize a new instance. This is normally called from the connect or
        connect_ssl context managers.

        poplib_pop3: pre-made poplib.POP3 or poplib.POP3_SSL instance
        username: username
        password: password
        """
        self.poplib_pop3 = poplib_pop3
        self.poplib_pop3.user(username)
        self.poplib_pop3.pass_(password)
        self.messages = self._request_list()

    def _request_list(self):
        """Request the list of messages from the server"""
        response, msg_infos, size = self.poplib_pop3.list()
        messages = OrderedDict()
        for msg_info in msg_infos:
            msg_num_string, size_string = msg_info.split()
            msg_num = int(msg_num_string)
            size = int(size_string)
            messages[msg_num] = Message(self, msg_num, size)
        return messages

    @property
    def greeting(self):
        """Server greeting"""
        return self.poplib_pop3.getwelcome()

    def _mark_for_deletion(self, num):
        """Mark message <num> for deletion"""
        if num not in self.messages:
            raise KeyError('Invalid message number %d' % num)
        self.poplib_pop3.dele(num)
        self.messages[num].marked_for_deletion = True

    def _email_from_lines(self, lines):
        """Parse email as email.message from lines as we get them from the server"""
        # lines as we get them from the poplib module are bytestrings, but the
        # email module needs a string. Which codec to use? Depends on the
        # encoding specified in the headers, I would think, but we don't know
        # that yet.
        # Use UTF-8 for now ...
        message = ''.join(line.decode('UTF-8') + '\n' for line in lines)
        return email.message_from_string(message)

    def _top(self, num, nr_lines_extra):
        """Retrieve header + nr_lines_extra lines from server as an email.message instance"""
        if num not in self.messages:
            raise KeyError('Invalid message number %d' % num)
        response, lines, size = self.poplib_pop3.top(num, nr_lines_extra)
        return self._email_from_lines(lines)

    def _retr(self, num):
        """Retrieve message <num> from server as an email.message instance"""
        if num not in self.messages:
            raise KeyError('Invalid message number %d' % num)
        response, lines, size = self.poplib_pop3.retr(num)
        return self._email_from_lines(lines)

    def reset_deletion_marks(self):
        """Reset all deletion marks"""
        self.poplib_pop3.rset()

    def close(self):
        """Close the connection. Normally handed for you by the context manager."""
        self.poplib_pop3.quit()

class connect:
    """Context manager for Pop3 without SSL"""
    def __init__(self, host, username, password, port=poplib.POP3_PORT, timeout=None):
        self.pop3 = Pop3(
            poplib.POP3(host, port, timeout),
            username,
            password
            )
    def __enter__(self):
        return self.pop3
    def __exit__(self, exc_type, exc_value, traceback):
        self.pop3.close()

class connect_ssl:
    """Context manager for Pop3 with SSL"""
    def __init__(self, host, username, password, port=poplib.POP3_SSL_PORT, keyfile=None, certfile=None, timeout=None, context=None):
        self.pop3 = Pop3(
            poplib.POP3_SSL(host, port, keyfile, certfile, timeout, context),
            username,
            password
            )
    def __enter__(self):
        return self.pop3
    def __exit__(self, exc_type, exc_value, traceback):
        self.pop3.close()

您还可以在https://gitlab.com/roelschroeven-unixtools/pop3tool上找到代码

Answer 1

干得好，这是一些非常干净的代码。有一些小的东西你可以改进，但在大多数情况下，这是可读的和重点。我将先讨论一些较小的问题，然后讨论你的主要问题。

• 模块级的文档字符串应该位于源代码文件的最顶端。这也清楚地表明，它属于整个模块，并不是特定代码的附加文档。
• "%"-formatting已经过时了，可能是一种痛苦，而且(可以说)很难读懂。幸运的是，有str.format，它解决了这些问题。
• 行不应超过79个字符，根据PEP8 8。某些场景允许您打破这条规则，比如使用多行字符串，或者在长行包装会损害可读性的情况下。非正式地说，限制通常是80个或100个字符。

我认为让Pop3类本身成为上下文管理器通常要简单得多，但是我创建了两个上下文管理器，而不是Pop3类，因为这允许我用最少的重复代码处理连接的代码。也许还有更好的方法？

严格地说，不需要connect和connect_ssl，所以您应该取消它们，让Pop3实现上下文管理器协议。

另一方面，我对当前的实现没有什么奇怪的地方(尽管如果您真的想过火，您应该创建一个Pop3SSL类以避免违反单一责任原则)，只要它适合您，就保持它的原样吧！