can you use global variables in functions python code example

Example 1: global variable python

#it is best not to use global variables in a function
#(pass it as an argument)
a = 'This is global a'
def yourFunction():
    global a
    return a[0:2]

Example 2: global variable python

a = 0

def testFor():
  global a 
  if(a == 0):
    	#run code