Program to top-up phone with conditions in Python

You can divide your whole program into parts, this way it becomes easy while debugging and increases modularity in the code.

You can divide into multiple functions like

• Selecting service.
• Add top-up
• Restart logic

Refractored code

AVAILABLE_SERVICES = {"Green", "Blue", "Red"} 
AVAILABLE_TOPUPS = {50, 100, 300, 500, 1000}


def select_service():
    while True:
        service = input("Please enter Green, Blue or Red: ").title()
        if service in AVAILABLE_SERVICES:
            print("Welcome to Top-up Service")
            break
    return service


def top_up(service):
    times_topup = int(input("How many times do you want to top up? "))
    topups_selected = []
    for _ in range(times_topup):
        while True:
            topup = int(input("Please enter 50,100,300,500 or 1000: "))
            if topup in AVAILABLE_TOPUPS:
                topups_selected.append(topup)
                break
            else:
                print("Try Again!, Wrong Top-up")

    print("Top up(s) information : ", topups_selected)
    print("Total top up(s): ", sum(topups_selected))


def process():
    restart = "Y"
    while restart == "Y":
        service = select_service()
        top_up(service)
        restart = input("Do you want to start again?,Y or else: ").upper()
    print("Thank you for using our service")


if __name__ == "__main__":
    process()

Output:

Please enter Green, Blue or Red: Blue
Welcome to Top-up Service
How many times do you want to top up? 2
Please enter 50,100,300,500 or 1000: 7
Try Again!, Wrong Top-up
Please enter 50,100,300,500 or 1000: 50
Please enter 50,100,300,500 or 1000: 10
Try Again!, Wrong Top-up
Please enter 50,100,300,500 or 1000: 100
Top up(s) information :  [50, 100]
Total top up(s):  150
Do you want to start again?,Y or else: Y
Please enter Green, Blue or Red: Red
...
...
...
Do you want to start again?,Y or else: n
Thank you for using our service

Code Review

• PEP-8 violations:

  • E231 - missing whitespace after ,
    • range(1,n+1) ⟶ range(1, n+1)
    • {50,100,300,500,1000} ⟶ {50, 100, 300, 500, 1000}
• Declare constants for services and top-ups instead of writing {"Blue", ...} and {50, ...} everywhere.
  • {"Blue", ...} ⟶ AVAILABLE_SERVICES = {"Green", "Blue", "Red"} Now you can use AVAILABLE_SERVICES instead of writing {"Blue", ...}
  • {50, ...} ⟶ AVAILABLE_TOPUPS = {50, 100, 300, 500, 1000}
• Use str.title when taking input for service, so "BLUE" would become "Blue".
• Use _ here for i in range(1, n+1) when you are not using i in the loop.
  • for i in range(1, n+1) ⟶ for _ in range(n)
  • What's the purpose of _ in python
• You can make AVAILABLE_SERVICES as frozenset to make immutable.
  • AVAILABLE_SERVICES = frozenset({"Green", "Blue", "Red"})
  • AVAILABLE_TOPUPS = frozenset({50, 100, 300, 500, 1000})

You can use pep8online^* to check if your code is in accordance with PEP-8 standard.

You can use black^* (code formatting tool)

black --line-length 79 your_file.py

_{* I'm not affiliated to pep8online and black.}

Make use of docstring

A docstring explains what the function does, the input it expects and what output it gives. It's pythonic to include docstrings in functions and classes just below the function or class definition. For example

def f():
     """This is a function"""

Irrelevant checks

In your while loop, you check if service is in your set and also do a similar check in the while loop's body, the latter is irrelevant, you should take advantage of the first check and refactor the code like this

service = input("Please enter Green, Blue or Red: ")
while service not in {"Green", "Blue", "Red"}:
        print("Try Again!, Wrong Service")
        service = input("Please enter Green, Blue or Red: ")
# service is valid because the while loop breaks
# continue the code here....

A similar approach can be done for top_up

Side note

This program does nor necessarily need a recursive approach, recursion tends to slower and takes more memory due to keeping temporaries in the stack frame, consider using a while loop instead.