variables - About num1 and num2 in python calculator -

why works if isn't there variable says value of num1 , num2 variables? mean, shouldn't necessary add input num1 , num2? quite confused , new @ coding

{

#returns sum of num1 , num2  def add(num1, num2):     return num1 + num2  #returns subtracting of num1 , num2  def sub(num1, num2):     return num1 - num2  #returns multiplying of num1 , num2  def mul(num1, num2):     return num1 * num2  #returns dividing of num1 , num2  def div(num1, num2):     return num1 / num2    def main():     operation = input("what want (+,-,*,/): ")     if(operation != "+" , operation != "-" , operation != "*" , operation != "/"):         #invalid operation         print("you must enter valid operation")     else:         var1 = int(input("enter num1: "))         var2 = int(input("enter num2: "))          if(operation == "+"):             print(add(var1, var2))          elif(operation == "/"):             print(div(var1, var2))          elif(operation == "-"):             print(sub(var1, var2))          else:             print(mul(var1, var2))  main()} 

you have input in code

the 2 lines are:

var1 = int(input("enter num1: ")) var2 = int(input("enter num2: ")) 

read 2 documentation blocks on python built-ins

• input() : https://docs.python.org/2/library/functions.html#input
• int() : https://docs.python.org/2/library/functions.html#int

then need understand how function calls work

the names assign parameters of function valid inside declaration, , not need same on code.

def my_function(fn_variable_name):     return fn_variable_name + 1  # calling directly print my_function(1) # outputs 2  # calling variable another_variable_name = 45 print my_function(another_variable_name) # outputs 46  # storing result in variable yet_another_variable_name = my_function(32) print yet_another_variable_name # outputs 33  # combining 2 var_1 = 23 var_2 = my_function(var_1) print var_1 # outputs 23 print var_2 # outputs 24