python中的作用域

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字数统计

参考链接： http://python.jobbole.com/86465/

块间的作用域

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>>> if 1 ==1:
...     name = 'peter'
... 
>>> print(name)
peter
>>> if i in range(10):
...     age = 1
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'i' is not defined
>>> if i in range(10):
...     age = i
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'i' is not defined
>>> for i in range(10):
...     age = i
... 
>>> print(age)
9

局部作用域

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>>> name = 'zhangsan'
>>> def f1():
...     name = 'lisi'
...     def f2():
...         name = 'wangwu'
...         print(name)
...     f2()
... 
>>> f1()
wangwu

学过函数，肯定知道最后f1()执行完会输出wangwu；我们先记住一个概念，Python==中有作用域链，变量会由内到外找，先去自己作用域去找，自己没有再去上级去找，直到找不到报错==。

终极版作用域

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>>> name = 'peter'
>>> def f1():
...     print(name)
... 
>>> def f2():
...     name = 'eric'
...     return f1
... 
>>> ret = f2()
>>> ret()
peter

分析代码，这里执行ret()函数其实就是执行了函数f1(),因为函数f2()最后返回调用f1(),f1()和f2()并没有什么关系，调用f1()在f1()的作用域里寻找name。

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>>> li = [lambda:x for x in range(10)]
>>> li
[<function <listcomp>.<lambda> at 0x7fb196ec0bf8>, <function <listcomp>.<lambda> at 0x7fb196ec0c80>, <function <listcomp>.<lambda> at 0x7fb196ec0d08>, <function <listcomp>.<lambda> at 0x7fb196ec0d90>, <function <listcomp>.<lambda> at 0x7fb196ec0e18>, <function <listcomp>.<lambda> at 0x7fb196ec0ea0>, <function <listcomp>.<lambda> at 0x7fb196ec0f28>, <function <listcomp>.<lambda> at 0x7fb196ebe048>, <function <listcomp>.<lambda> at 0x7fb196ebe0d0>, <function <listcomp>.<lambda> at 0x7fb196ebe158>]
>>> type(li)
<class 'list'>
>>> type(li[0])
<class 'function'>
>>> print(li[0])
<function <listcomp>.<lambda> at 0x7fb196ec0bf8>
>>> print(li[0]())
9