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HomeBackend DevelopmentPython Tutorial详解Python函数作用域的LEGB顺序

详解Python函数作用域的LEGB顺序

Jun 10, 2016 pm 03:04 PM
pythonfunction scopeorder

本文为大家介绍了Python函数作用域的查找顺序,供大家参考,具体内容如下

1.什么是LEGB?
L:local 函数内部作用域
E:enclosing 函数内部与内嵌函数之间
G:global 全局作用域
B:build-in 内置作用域

2.LEGB是作什么用的?
为什么非要介绍这个呢?或者说它们的作用是什么?
原因是因为我们的在学习Python函数的时候,经常会遇到很多定义域的问题,全部变量,内部变量,内部嵌入的函数,等等,Python是如何查找的呢?以及Python又是按照什么顺序来查找的呢?这里做一个顺序的说明

3.顺序是什么
跟名字一样,Python在函数里面的查找分为4种,称之为LEGB,也正是按照这种顺序来查找的。

首先,是local,先查找函数内部
然后,是enclosing,再查找函数内部与嵌入函数之间(是指在函数内部再次定义一个函数)
其次,是global,查找全局
最后,是build-in,内置作用域

4.举例说明
ex1

passline = 60

def func(val):
  if val >= passline:
    print('pass')
  else:
    print('failed')

func(89)  

'''''''''''' 
pass
[Finished in 0.2s] 
''''''''''''

Python函数首先查找local,在局部变量作用域里并没有passline的定义,然后发现函数内部并没有内嵌函数,这时Python开始查找global,在全局里查找到passline的定义,被调用。

ex2

def Max(val1, val2):
  return max(val1, val2)

print(Max(90, 100))

'''''''''
100
[Finished in 0.1s]
'''''''''

Max函数里面直接调用另外一个函数,调用的max()(注意两个函数的大小写不一样),该函数并没有被定义,但是却属于我们上述的第四种,属于build-in函数,既是在python标准库里的函数,内置的,可以直接调用的。最后一步才会查找到这里

关于第二种,属于内嵌函数,即使在函数里面再次定义一个函数,这时会首先查找local函数里面是否有定义,然后才会查找函数里面内嵌函数里面有没有定义,这一种有专门的名词,叫做闭包,闭包在之前一些文章中都有介绍,希望大家阅读。

以上就是本文的全部内容,希望对大家的学习有所帮助。

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