Did you do something like this?

x = 1 # make a global

def f():
      print x # try to print the global
      ...
      for j in range(100):
           if q>3:
              x=4

Any variable assigned in a function is local to that function, unless it is specifically declared global. Since a value is bound to x as the last statement of the function body, the compiler assumes that x is local. Consequently the "print x" statement attempts to print an uninitialized local variable and will trigger a NameError.

The solution is to insert an explicit global declaration at the start of the function:

def f():
      global x
      print x # try to print the global
      ...
      for j in range(100):
           if q>3:
              x=4

In this case, all references to x are interpreted as references to the x from the module namespace.

Note that the global declarations should be placed at the beginning of the function, and that it affects all uses of the variable inside the function.

CATEGORY: programming

last updated 2 years ago by effbot #