[Tutor] "local variable 'l1' referenced before assignment"

[Alan Gauld]

"Dick Moores" <rdm at rcblue.com> wrote


> I'm puzzled by the below error msg. If I change the line in a2() 
> from
>
> l1 = [1,2,3]*100

This is not in a2() this is in the global namespace outside of a2.
a2() consists of a single assignment statement. And assignment
inside a function creates a local variable which in this case
masks the global variable. But the local variable assignment
uses the same variable which is not allowed so you get the
error message.

> Why? And why isn't that line a problem for a1()?

In a1 you don't assign so you never create a local variable
you use the global variable


> =========================================
> def a1():
>        return l1.extend(l2)

No assignment, it returns the global value

> if __name__=='__main__':
>        l1 = [1,2,3]*100
>        t = Timer("a1()", "from __main__ import a1")


> def a2():
>        l1 += l2

new local variable "created" but erroneously. Change to

def a2():
     global I1
     I1 += I2
     return I1

See my tutor topic on namespaces for more on this theme.

HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld