全局变量-如何在引用后分配变量？

Question

With python, the language has a useful feature which is "global", however, I saw that when experimenting with code that after I assign a global variable as an integer or value, I could use the variable but I can't change the variable after I reference it?

if you do not understand what i just wrote there, here is my sample code:

global number
number = 5

text="hello"

if text+str(number)=="hello5":
    number=number+1

After I run this specific code I get an error, it states:

UnboundLocalError: local variable 'number' referenced before assignment

If you can help please state how I can make this code run "properly".

Answer 1

The global keyword should actually be use in a local scope to reference the global variable. For example

c = 0
def add():
  global c
  c = c + 2

Using the global keyword in the function add(), we were able to access the variable c and change it accordingly.

Answer 2

Is this your full code? If so; you'd use the 'global' command inside your functions to indicate that any reference to that variable should be taken from the global namespace rather than the local namespace, effectively allowing you to share a variable between functions without needing to pass them as parameters.

Your code here is stating that the variable 'number' is global, however since 'number' has not yet been declared and assigned a value, you're getting this error.

You only need to specify that a variable is global when you enter a different namespace (ie enter a function). And you do this INSIDE that function, rather than upon first declaration of the variable.

Hope this helps