Python 中的那些坑总结—

1.三元表达式之坑

很显然，Python把第一行的（10 + 4）看成了三元表达式的前部分，这个坑是看了《Python cookbook》(P5)中学到的，书中的代码：

2.Python生成器(yield)+递归

前两天一直纠结python的生成器递归该怎么写，今天看了os.walk()的代码恍然大悟，编程真是博大精深啊！不多说，上代码：

from os import path

def walk(top, topdown=True, onerror=None, followlinks=False):

    islink, join, isdir = path.islink, path.join, path.isdir

    try:

        # Note that listdir and error are globals in this module due

        # to earlier import-*.

        names = listdir(top)

    except error, err:

        if onerror is not None:

            onerror(err)

        return

    dirs, nondirs = [], []

    for name in names:

        if isdir(join(top, name)):

            dirs.append(name)

        else:

            nondirs.append(name)

    if topdown:

        yield top, dirs, nondirs

    for name in dirs:

        new_path = join(top, name)

        if followlinks or not islink(new_path):

            for x in walk(new_path, topdown, onerror, followlinks):  # 生成器递归

                yield x

    if not topdown:

        yield top, dirs, nondirs

3.try...finally + return:

　　如果写了try模块内有return且最后还有finally，那么会执行return后再执行finally。

　　这是从Queue的get方法里看到的，贴上自己写的测试代码：

　　附加Queue的get方法：

# Queue.py

......

    def get(self, block=True, timeout=None):

        self.not_empty.acquire()

        try:

            if not block:

                if not self._qsize():

                    raise Empty

            elif timeout is None:

                while not self._qsize():

                    self.not_empty.wait()

            elif timeout < 0:

                raise ValueError("'timeout' must be a non-negative number")

            else:

                endtime = _time() + timeout

                while not self._qsize():

                    remaining = endtime - _time()

                    if remaining <= 0.0:

                        raise Empty

                    self.not_empty.wait(remaining)

            item = self._get()

            self.not_full.notify()

            return item

        finally:

            self.not_empty.release()

巴特西

Python 中的那些坑总结——持续更新

1.三元表达式之坑

2.Python生成器(yield)+递归

3.try...finally + return:

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