While loop conditional expression local variable behavior

Asked May 31 '22 at 18:16

Active May 31 '22 at 18:19

Viewed 41 times

-1

What is the behavior of local variables in while loops? I would have imagined the value of a would be taken from the global variable external to the function. Is there some kind of rule which excludes global variables from within the conditional expression of a while statement? It seems to detect that a is not defined within the function. If i change the while loop to an if statement using the same variable a, there is no local unbound error

Ofcourse i could jsut move the assignment of a into the function, but im interested in the behaviour of local variables in while loop expressions

FiboList = []
a, b = 0, 1
def i_fibonacci(n):
    while a < n:
        FiboList.append(a)
        a, b = b, a+b



File "c:\Users\Dell\Desktop\PythonPlayground\fibonacci.py", line 30, in i_fibonacci
        while a < n:
    UnboundLocalError: local variable 'a' referenced before assignment

edited May 31 '22 at 18:18

asked May 31 '22 at 18:16

ThreadBucks

1

it's the `def`, not the `while` that creates a new name scope – Kurt May 31 '22 at 18:19
1

You can thoroughly enjoy reading about [scopes in Python](https://docs.python.org/3/tutorial/classes.html#python-scopes-and-namespaces) – sudden_appearance May 31 '22 at 18:19
a, b = 0, 1 def i_fibonacci(n): if(a != 5): print(True) No errors – ThreadBucks May 31 '22 at 18:20
Do you *call* `i_fibonacci` anywhere? – Scott Hunter May 31 '22 at 18:21
2

"If i change the while loop to an if statement using the same variable a, there is no local unbound error" If I do that, I get the same error ([proof](https://ideone.com/qpKSKN)), so I'd wager you changed more than just replacing the `while` with an `if`. – sepp2k May 31 '22 at 18:22
You must make sure to call `i_fibonacci` after the `a, b = 0, 1` line. – bjhend May 31 '22 at 18:23
Thank you, i would have found the documentation without your help. Obviously im looking for a specific answer...# – ThreadBucks May 31 '22 at 18:24
@bjHend it is called after the assignments – ThreadBucks May 31 '22 at 18:24
This will give you an error with either `if` or `while`: `if a < n: print(True); a=n` – PM 77-1 May 31 '22 at 18:31
The first *duplicate* link gives the answer. – PM 77-1 May 31 '22 at 18:33
I think the pre-requisite condition here for when the error appears in when the variable is apart of an assignment statement, including within if and while statements – ThreadBucks May 31 '22 at 18:45

While loop conditional expression local variable behavior

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