Python how to use inputs from sub routines in another sub routine

I have a problem to solve in Python whereby the user inputs variables such as number of items they want to buy. I've got this as a def customer, with an output 'how many widgets would you like' and then their input multiplied by a price of say £10. This bit works fine.

I want to take that input of theirs to another subroutine to do further maths on, such as tax, and total. Are there some keywords for me to study so I can do this?

Here is my code so far:

def wall_1():
   height = int(input("Enter the height in metres of wall 1 : "))
   width = int(input("Enter the width in metres of wall 1 : "))
   wall_1_price = height * width
   price_all_walls(wall_1_price)
def wall_2():
   height = int(input("Enter the height in metres of wall 2 : "))
   width = int(input("Enter the width in metres of wall 2 : "))
   wall_2_price = height * width
   price_all_walls(wall_2_price)
def wall_3():
   height = int(input("Enter the height in metres of wall 3 : "))
   width = int(input("Enter the width in metres of wall 3 : "))
   wall_3_price = height * width
   price_all_walls(wall_3_price)
def wall_4():
   height = int(input("Enter the height in metres of wall 4 : "))
   width = int(input("Enter the width in metres of wall 4 : "))
   wall_4_price = height * width
   price_all_walls(wall_4_price)
def price_all_walls(wall_1_price, wall_2_price, wall_3_price, wall_4_price): 
   print("The total price so far is : " + 
       str(wall_1_price + wall_2_price + wall_3_price + wall_4_price))


if __name__ == "__main__":

   wall_1()
   wall_2()
   wall_3()
   wall_4()
   price_all_walls()

This code sample will solve your problem. The price_all_walls method accepts four arguments. In your wall_1(), wall_2(), wall_3() and wall_4() methods, you are calling the price_all_walls() with only one argument (the price of the wall). This will throw an error "the function definition does not exist".

When you define a function, a function prototype is associated to it (although this term is most commonly used in C and C++ programming languages), which includes the method's name and the type signature (parameter types -> not applicable in python, return type etc.). When you call the method price_all_walls(), it should be called with four arguments and hence your code could be modified as follows:

def wall_1():
   height = int(input("Enter the height in meters of wall 1 :"))
   width = int(input("Enter the width in meters of wall 1:"))
   wall_1_price = height * width
   wall_2(wall_1_price)

def wall_2(wall_1_price):
   height = int(input("Enter the height in meters of wall 2:"))
   width = int(input("Enter the width in meters of wall 2:"))
   wall_2_price = height * width
   wall_3(wall_1_price, wall_2_price)

def wall_3(wall_1_price, wall_2_price)
   height = int(input("Enter the height in meters of wall 3:"))
   width = int(input("Enter the width in meters of wall 3:"))
   wall_3_price = height * width
   wall_4(wall_1_price, wall_2_price, wall_3_price)

def wall_4(wall_1_price, wall_2_price, wall_3_price):
   height = int(input("Enter the height in meters of wall 4:"))
   width = int(input("Enter the width in meters of wall 4:"))
   wall_4_price = height * width
   price_all_walls(wall_1_price, wall_2_price, wall_3_price, wall_4_price)

def price_all_walls(wall_1_price, wall_2_price, wall_3_price, wall_4_price):
   print("The total price so far is : " + str(wall_1_price + wall_2_price + wall_3_price + wall_4_price))

if __name__=="__main__":
   wall_1()

Although this is a very inefficient way of doing this (no good programmer will ever suggest this). This example provides a good explanation to the question at hand.

If you would want to code this problem, I'd suggest you make use of a global variable or do it the way shown in the code below:

def wall_1():
   height = int(input("Enter the height of wall 1 :"))
   width = int(input("Enter the width of wall 1 :"))
   wall_1_price = height * width
   return wall_1_price

def wall_2():
   height = int(input("Enter the height of wall 2:"))
   width = int(input("Enter the width of wall 2:"))
   wall_2_price = height * width
   return wall_1_price

def wall_3():
   height = int(input("Enter the height of wall 3:"))
   width = int(input("Enter the width of wall 3:"))
   wall_3_price = height * width
   return wall_3_price

def wall_4():
   height = int(input("Enter the height of wall 4:"))
   width = int(input("Enter the width of wall 4:"))
   wall_4_price = height * width
   return wall_4_price

def price_all_walls(wall_1_price, wall_2_price, wall_3_price, wall_4_price):
   return wall_1_price + wall_2_price + wall_3_price + wall_4_price

if __name__=="__main__":
   wall_1_price = wall_1()
   wall_2_price = wall_2()
   wall_3_price = wall_3()
   wall_4_price = wall_4()
   print("The total price of the walls is : " + str(price_all_walls(wall_1_price, wall_2_price, wall_3_price, wall_4_price)))

Although anyone would suggest that the best way to do this would be as follows. Declare a function wall_n(int, int) that takes the height and width as arguments and returns the price of the wall. This leads to modular code and also provides re usability.

def wall_n(height, width):
   wall_n_price = height * width 
   return wall_n_price

def price_all_walls(prices):
   total_price = 0
   for price in prices:
      total_price += price
   return total_price

if __name__=="__main__":
   number_walls = int(input("Enter the number of walls to build : "))
   wall_prices = []
   for i in range(number_walls):
      height = int(input("Enter the height of wall " + str(i) + " : "))
      width = int(input("Enter the width of wall " + str(i) + " : "))
      wall_prices.append(wall_n(height, width))
   print("The total price is : " + str(price_all_walls(wall_prices)))

I have not demonstrated the use of global variables. You can read about it here

I hope this answers your question.