python中那些鲜为人知的功能特性

经常逛GitHub的可能关注一个牛叉的项目，叫 What the f*ck Python!

这个项目列出了几乎所有python中那些鲜为人知的功能特性，有些功能第一次遇见时，你会冒出 what the f**k 的感叹。

因为这些例子看起来反人类直觉。

但是如果你理解了它背后的真正原理，你又会惊叹what the f**k， 竟然还有这么骚的操作。

来看看几个例子吧。

微妙的字符串

>>> a = "wtf"
>>> b = "wtf"
>>> a is b
True

>>> a = "wtf!"
>>> b = "wtf!"
>>> a is b
False

>>> a, b = "wtf!", "wtf!"
>>> a is b 
True # 3.7 版本返回结果为 False.
复制代码

出乎意料的"is"

>>> a = 256
>>> b = 256
>>> a is b
True

>>> a = 257
>>> b = 257
>>> a is b
False

>>> a = 257; b = 257
>>> a is b
True
复制代码

说好的元组不可变呢

some_tuple = ("A", "tuple", "with", "values")
another_tuple = ([1, 2], [3, 4], [5, 6])


>>> some_tuple[2] = "change this"
TypeError: 'tuple' object does not support item assignment
>>> another_tuple[2].append(1000) # 这里不出现错误
>>> another_tuple
([1, 2], [3, 4], [5, 6, 1000])
>>> another_tuple[2] += [99, 999]
TypeError: 'tuple' object does not support item assignment
>>> another_tuple
([1, 2], [3, 4], [5, 6, 1000, 99, 999])
复制代码

消失的全局变量

e = 7
try:
    raise Exception()
except Exception as e:
    pass
复制代码

输出

>>> print(e)
NameError: name 'e' is not defined
复制代码

到底返回哪个值

def some_func():
    try:
        return 'from_try'
    finally:
        return 'from_finally'
复制代码

输出

>>> some_func()
'from_finally'