Can somebody point me out how the global statement is used in python ? Is ti only nescesery when i want to assign a value to a global variable inside a function ?
Btw
let’s say that if i have the following code :
ex.1
y=5
def x ():
print y
x()
ex.2
y=5
def x();
global y
y=23
print y
x()
is the global statement needed only in the second code in order to assign the value ?
Global gives you access to define where variables can be used.
For instance, if you declare a variable to be global inside of a function, then you can then use the value associated with that variable outside of that function. Similarly if you have a variable and you declare its access to be global, then when you assign into it in a function it will change the global value, otherwise it will change only the value designated to the namespace of the function.
For instance
y = 5
def f():
y = 30
print y #print 30
f()
def fb():
global y
y = 50
fb()
print y #prints 50, back in global namespace
def fa():
global z
z = 20
fa()
print z #prints 20
I suggest playing around with it to get it to work properly, but keep in mind that python will resolve name issues from the most interior namespace outward. If there is a global variable var and a local variable var, then the local variable will take precedence over the global variable. If you reference var inside of a function, and there is no local var, python will start looking in the global namespace (or next highest namespace) for var. This is why its good programming practice to adopt a different naming scheme for local and global variables. In general I do the following: