Reassigning value to a variable inside a function in python

Question

I want to run an infinite loop and at every 100th loop i want to print. If I do this : it works perfectly,

delay=0

while 1:
delay=delay+1
print(delay)
if delay>100:
    delay=0
    print('100th time')

However if I put my if statement in a function it gives error:

delay=0
def foo():
    if delay>100:
        delay=0
        print('100th time')
while 1:
    delay=delay+1
    print(delay)
    foo()

The error is : UnboundLocalError: local variable 'delay' referenced before assignment.

Is there anyway I can do the reassignment in a function? Putting the entire thing in my while loop would be problematic for me.

Shivam Singh · Answer 1 · 2018-05-22T07:35:46.253

2

You can use global, if you do not want pass delay as an argument to foo. But it is better to do it that way. Also read: Why are global variables evil?

delay=0
def foo():
    global delay
    if delay>100:
        delay=0
        print('100th time')
while 1:
    delay=delay+1
    print(delay)
    foo()

edited May 22 '18 at 07:35

answered May 22 '18 at 07:24

Shivam Singh

1,584
1
10
9

1

While this works, there are probably solutions without resorting to use `global`. – Reut Sharabani May 22 '18 at 07:29
I agree, this is just one of the ways. – Shivam Singh May 22 '18 at 07:30

Shubham · Answer 2 · 2018-05-22T07:36:50.890

You can use global declaration inside the function as shown below:

delay=0
def foo():
    global delay
    if delay>100:
        delay=0
        print('100th time')
while 1:
    delay=delay+1
    print(delay)
    foo()

You can also avoid global in this case by passing the value in the function foo() ans reassign delay like delay = (delay + 1) % 100.

delay=1
def foo(delay):
    if delay == 0:
        print('100th time')
while True:
    delay = delay + 1
    print(delay)
    foo(delay)
    delay = delay % 100

Reut Sharabani · Accepted Answer · 2018-05-22T07:30:27.360

0

Pass delay to the function and use modulu(%):

delay=0
def foo(delay):
    if delay % 100 == 0:
        print('100th time')

while True:
    delay=delay+1
    print(delay)
    foo(delay)

Always avoid using globals when other effective solutions exist. They increase the complexity of the code significantly.

edited May 22 '18 at 07:30

answered May 22 '18 at 07:27

Reut Sharabani

30,449
6
70
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This should be the accepted answer, since it avoids the global variable, which is preferable. – Zinki May 22 '18 at 07:29
But this `delay` is still a global, it's just that it's being modified by global code, not code inside a function. – PM 2Ring May 22 '18 at 07:32
It is modified in its own context, `global` is used to modify global variables in local context, which makes things more complex (usually with no need). The other added value is that `foo` is now a function of its' parameters and does not depend on an external state (easier to reason about, easier to test and debug). – Reut Sharabani May 22 '18 at 07:41

Reassigning value to a variable inside a function in python

3 Answers3