notes ： This article is reprinted to CSDN Blogger 「onlyanyz」 The original article of
Link to the original text ：https://blog.csdn.net/onlyanyz/article/details/45009697
We write Python When , Sometimes it happens ： Clearly, variables have been defined outside the function n, Print the value inside the function first , Then make the variable increase by itself , The runtime encountered such an error ：
UnboundLocalError： local variable ‘xxx’ referenced before assignment
As shown in the following code chip ：
n=0
def func():
print n
n+=1
func()
As a result, the error mentioned above appears at runtime .
This is because After modifying the variable assignment inside the function , The variable will be Python The interpreter thinks it's a local variable, not a global variable , When the program is executed to n+=1 When , Because this sentence is for n assignment , therefore n Becomes a local variable , Then in execution print n When , because n This local variable has not been defined yet , It's natural to throw such a mistake .
Consider the following code snippet ：
n=0
def func():
print n
func()
Because there's no such thing as n assignment , So then ,print n What you print is a global variable n Value .
that , How do we get to print first inside a function , What about reassignment ？ The conclusion is to use global keyword , Declare inside the function n This variable is a global variable . The code is as follows ：
n=0
def func():
global n
print n
n+=1
func()
print n
give the result as follows ：
0
1
[Finished in 1.0s]
At this time ,n It becomes a global variable , Modify the variable inside the function , There will be no problem .
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Link to the original text ：https://blog.csdn.net/onlyanyz/article/details/45009697
