lesson-20.py

#!/usr/bin/env python3

# lesson-20.py - eliminate global variable by passing around balance
#
# Learn:
#     avoid globals by passing variables
#     keep global space unpolluted

import sys

def showBalance(balance):
    print('Your balance is $%d.' % balance)
    print()

def showTransactions(transactions, balance):
    print('   op      amount  balance')
    print('--------  -------  -------')
    print('                   %7d  (starting)' % balance)
    for transaction in transactions:
        [op, amount] = transaction
        if op == 'w':
            opLabel = 'withdraw'
            balance -= amount
        else:
            opLabel = "deposit"
            balance += amount
        print('%-8s  %7d  %7d' % (opLabel, amount, balance))
    print()

def withdrawal(amount, balance, transactions):
    if amount > balance:
        print("Sorry, you don't have that much!")
    else:
        print('Withdraw $%d.' % amount)
        balance -= amount
        transactions.append(['w', amount])
        showBalance(balance)
    return (balance, transactions)

def deposit(amount, balance, transactions):
    print('Deposit $%d.' % amount)
    balance += amount
    transactions.append(['d', amount])
    showBalance(balance)
    return (balance, transactions)

def getOperation():
    op = input('Enter d for deposit, w for withdrawal, t for transactions, or q to quit: ')
    if op != 'q' and op != 'd' and op != 'w' and op != 't':
        print('Invalid operation.  Please try again.')
        op = None
    return op

def getAmount():
    amount = None
    try:
        amount = int(input('Enter amount: '))
        if amount <= 0:
            print('The amount must be positive.')
            amount = None
    except:
        print('Invalid amount.  Please try again.')

    return amount

def getStartingBalance(balance):
    if len(sys.argv) > 1:
        try:
            balance = int(sys.argv[1])
            if balance < 0:
                print('The balance cannot be negative.')
                balance = None
        except:
            print('Invalid starting balance.')
            print('usage: %s [amount]' % sys.argv[0])
            print('where amount is a starting balance dollar amount')
            balance = None
    return balance

def processTransactions(balance):
    startingBalance = balance
    transactions = []
    while True:
        amount = None
        op = getOperation()
        if op == 'q':
            break
        elif op == 't':
            showTransactions(transactions, startingBalance)
        elif op is not None:
            amount = getAmount()

        if amount is None:
            pass
        elif op == 'd':
            (balance, transactions) = deposit(amount, balance, transactions)
        else:
            (balance, transactions) = withdrawal(amount, balance, transactions)

def main():
    balance = 100
    balance = getStartingBalance(balance)

    if balance is not None:
        print('Welcome to the bank.')
        showBalance(balance)
        processTransactions(balance)

main()