I have code that looks similar to this
v = '0'
def program():
x = input('1 or 2 ')
if x == '1':
print('it is 1')
v = '1'
elif x == '2':
print('it is 2')
v = '2'
while True:
program()
print(v)
However, when I run this code the variable 'v' always prints out the default 0. Why isn't it giving me the variable I assigned it in the function?
You have two variables named v:
v=0 declaration at the top.v in program.First of all, you really shouldn't use globals in functions, as it is bad programming practice. You should pass it as a parameter and return with any other results.
If you really must, you can modify a global variable in a function by first declaring it as a global variable.
Also note that you need to use raw_input in Python 2.
def program():
global v
x = raw_input('1 or 2 ')
if x == '1':
print('it is 1')
v = '1'
elif x == '2':
print('it is 2')
v = '2'
Using global variables in a function other than the one that created them
Your function manipulates a local copy of variable v. If you want to get the value of v after calling program(), append return v to the end of your function definition.
That is:
v = '0'
def program():
x = input('1 or 2 ')
if x == '1':
print('it is 1')
v = '1'
elif x == '2':
print('it is 2')
v = '2'
return v
while True:
v = program()
print(v)
If you don't want to return anything, you can set v to the globally declared variable as so:
v = '0'
def program():
x = input('1 or 2 ')
if x == '1':
print('it is 1')
global v
v = '1'
elif x == '2':
print('it is 2')
global v
v = '2'
while True:
program()
print(v)
To complement the duplicate flag, here is an explanation with respect to your code:
You need to explicitly tell your method that you want to use the global v, otherwise, it will never get updated from what is happening to the v within the method scope.
To rectify this, you want to add global v inside your method:
def program():
global v
# rest of your code here
That should work.
Variable assignments in Python are locally scoped. If you want to manipulate a global state (or an enclosing state) inside of a function, you can wrap that state in a holder and then reference the holder. For example:
v = ['0']
def program():
x = input('1 or 2 ')
if x == '1':
print('it is 1')
v[0] = '1'
elif x == '2':
print('it is 2')
v[0] = '2'
while True:
program()
print(v[0])
The above segment references an array and manipulates the value inside of the array.
