Python by Swaroop C H - HTML preview

Using the global statement

If you want to assign a value to a name defined outside the function, then you have to tell Python that the name is not local, but it is global. We do this using theglobal statement. It is impossible to assign a value to a variable defined outside a function without theglobal statement.

You can use the values of such variables defined outside the function (assuming there is no variable with the same name within the function). However, this is not encouraged and should be avoided since it becomes unclear to the reader of the program as to where that variable's definition is. Using theglobal statement makes it amply clear that the variable is defined in an outer block.

Example 7.4. Using the global statement

#!/usr/bin/python
# Filename: func_global.py
def func():
global x

print 'x is', x
x = 2
print 'Changed global x to', x

x = 50
func()
print 'Value of x is', x

Output

$ python func_global.py x is 50
Changed global x to 2 Value of x is 2

How It Works

Theglobal statement is used to decare thatx is a global variable - hence, when we assign a value tox inside the function, that change is reflected when we use the value ofx in the main block. You can specify more than one global variable using the sameglobal statement. For example,global x, y, z.