global variables - UnboundLocalError in Python -

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• how change variable after defined in python 5 answers

what doing wrong here?

counter = 0  def increment():   counter += 1  increment() 

the above code throws unboundlocalerror.

python doesn't have variable declarations, has figure out scope of variables itself. simple rule: if there assignment variable inside function, variable considered local.^[1] thus, line

counter += 1 

implicitly makes counter local increment(). trying execute line, though, try read value of local variable counter before assigned, resulting in unboundlocalerror.^[2]

if counter global variable, global keyword help. if increment() local function , counter local variable, can use nonlocal in python 3.x.