python中鲜为人知的功能特性有哪些
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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.
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
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])
消失的全局变量
e = 7
try:
raise Exception()
except Exception as e:
pass
输出
>>> print(e)
NameError: name 'e' is not defined
try 遇到 finally到底返回哪个值
def some_func():
try:
return 'from_try'
finally:
return 'from_finally'
输出
>>> some_func()
'from_finally'
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