The global statement tells Python that a function plans to change one or more global names.
Global names are variables assigned at the top level of the enclosing module file.
Global names may be referenced within a function without being declared.
X = 88 # Global X def func(): global X # from ww w .jav a2s.c om X = 99 # Global X: outside def func() print(X) # Prints 99
Here, we've added a global declaration to the example here, such that the X inside the def now refers to the X outside the def.
Consider the following code
y, z = 1, 2 # Global variables in module def all_global(): global x # Declare globals assigned x = y + z # No need to declare y, z: LEGB rule # from w w w . ja v a 2 s.c om
Here, x, y, and z are all globals inside the function all_global.
y and z are global because they aren't assigned in the function.
x is global because it was listed in a global statement to map it to the module's scope explicitly.
Without the global here, x would be considered local by virtue of the assignment.