Python 中的那些坑总结——持续更新

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()