UnboundLocalError: local variable 'pi' referenced

redstoneleo

于 2017-04-09 14:00:46 发布

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本文详细解释了Python中局部变量与全局变量的区别及使用规则，包括变量声明为global的情况以及未声明时默认行为的说明，并通过示例展示了如何正确处理变量的作用域。

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In Python, variables that are only referenced inside a function are implicitly global. If a variable is assigned a value anywhere within the function’s body（即便没用到）, it’s assumed to be a local unless explicitly declared as global.

https://docs.python.org/3/faq/programming.html#what-are-the-rules-for-local-and-global-variables-in-python

>>> from math import pi
>>> pi
3.141592653589793
>>> def s():
	if pi:
		print('if pi')
	else:
		print('in else')

		
>>> s()
if pi
>>> def s():
	if pi:
		print('if pi')
		pi=3
	elif pi<3:
		print('elif pi<3')

		
>>> s()
Traceback (most recent call last):
  File "", line 1, in 
    s()
  File "", line 2, in s
    if pi:
UnboundLocalError: local variable 'pi' referenced before assignment