NameError: name 'one' is not defined python 3.4 error

Question

a=str(input("Enter num To Start FunctionOne"))
if(a == '1'):
    one()



elif (a == '2'):
    tow()




def one():
    print('Good')

def tow():
    print('Very Good')

Error

Enter numper To Start FunctionOne1
Traceback (most recent call last):
  File "C:/Users/Hacker/Desktop/complex program.py", line 3, in <module>
    one()
NameError: name 'one' is not defined

Answer 1

You need to define the functions before calling them:

def one():
    print('Good')

def tow():
    print('Very Good')

a=str(input("Enter num To Start FunctionOne"))
if(a == '1'):
    one()



elif (a == '2'):
    tow()

If you call a function but the function is defined below it then it won't work because Python doesn't know yet what that function call is supposed to do.

Answer 2

Define your functions before using them

Python is an interpreted language, so the interpreter moves line by line, you are trying to call the function - one() before it has been defined, in the later parts of the program. You should move the function definitions before calling part -

def one():
    print('Good')

def tow():
    print('Very Good')

a=str(input("Enter num To Start FunctionOne"))
if(a == '1'):
    one()

elif (a == '2'):
    tow()

Answer 3

Python reads the script line by line, so when it reaches the one() function call, it throws the error because is not defined yet.

Answer 4

Don't put any instructions in the script other than function definitions. Then call the main function in a clause at the bottom. This lets the interpreter see everything defined before trying to call it:

def main():
    a = input("Enter num To Start FunctionOne")
    if a == '1':
        one()
    elif a == '2':
        two()

def one():
    print('Good')

def two():
    print('Very Good')

if __name__ == '__main__':
    main()