Python's Variable scope detail

#定义变量a

The code is as follows	Copy Code
>>> A = 0 >>> Print a

0# definition function P ()

The code is as follows	Copy Code
>>> def p (): ... print a ... >>> P ()

0# definition function P2 ()

The code is as follows	Copy Code
>>> def p2 (): ... print a .. A = 3 ... print a ...

>>> P2 () # Run error, external variable A is referenced first, cannot be assigned again

The code is as follows	Copy Code
Traceback (most recent call last): File "<interactive input>", line 1, in <module> File "<interactive input>", line 2, in P2 Unboundlocalerror:local variable ' A ' referenced before assignment# definition function p3 () >>> def P3 ():

. A = 3 # do not reference direct assignment

The code is as follows	Copy Code
... print a ... >>> P3 () 3 >>> Print a

0 # External variable A does not change