An account that refuses – Python Practice Problem

Run an account with its own kinds of error.

What to build

Two custom exceptions, raised by a function and handled by its caller.

Requirements

Define BadAmount and NotEnough, both inheriting from Exception.
deposit X and withdraw X change the balance, which starts at 0.
An amount of 0 or less raises BadAmount. Print Refused: bad amount.
Withdrawing more than the balance raises NotEnough with the shortfall. Print Refused: need X more.
Count every command with finally, and finish with Balance B and Processed P.

Input

The first line has n. Each of the next n lines is deposit X or withdraw X.

Output

One line for each refusal, then the two final lines.

Constraints

n is from 1 to 100. Each X is a whole number from -1000 to 100000.

Example

Input:

3
deposit 100
withdraw 150
withdraw 30

Output:

Refused: need 50 more
Balance 70
Processed 3

Why it works

Each exception names one kind of problem, so the caller's except blocks stay simple. finally counts a command however it ended.

Examples

Example 1 · Input

3
deposit 100
withdraw 150
withdraw 30

Expected output

Refused: need 50 more
Balance 70
Processed 3

Example 2 · Input

2
deposit -5
withdraw 0

Expected output

Refused: bad amount
Refused: bad amount
Balance 0
Processed 2

Prompts inside input() are ignored when checking, so input("n: ") is fine.

Hints

Hint 1

Define two classes that inherit from Exception.

Hint 2

In withdraw, check for a bad amount first and then for too little money.

Hint 3

Put processed += 1 in a finally block.

Solution

Show one correct solution (try it yourself first)

class BadAmount(Exception):
    pass

class NotEnough(Exception):
    pass

balance = 0

def apply(command, amount):
    global balance
    if amount <= 0:
        raise BadAmount()
    if command == "deposit":
        balance += amount
    else:
        if amount > balance:
            raise NotEnough(amount - balance)
        balance -= amount

n = int(input())
processed = 0
for _ in range(n):
    command, text = input().split()
    try:
        apply(command, int(text))
    except BadAmount:
        print("Refused: bad amount")
    except NotEnough as error:
        print(f"Refused: need {error} more")
    finally:
        processed += 1
print("Balance", balance)
print("Processed", processed)

Lesson: Raising your own errors →