Simple scripts to play with scope in R and Python

banking.py

# Ross is a programmer for Megabank, working on a new smartphone app that
# helps users transfer money between accounts. He's relatively new to
# Python, the language preferred by the top brass, and is not entirely
# sure how functions handle global variables.

# Ross opens a bank account, then uses the app to perform a series of
# transactions. Because he's no fool, he does so in the lobby of a
# Megabank branch, and the bank teller informs him after each step what
# his balance is. If everything is working correctly, Ross should be
# able to take back out exactly what he put in... unless the app is not
# working!

from sys import exit

total = 130
print("Ross opens a new account with $", total)

def deposit(amount):
    global total
    if amount <= 0:
        exit("Deposits must be positive!")
    total += amount
    print("${0} deposited. Your app balance is ${1}".format(amount, total))

def withdraw(amount):
    global total
    if amount > total:
        exit("You don't have that much money!")
    total -= amount
    print("${0} withdrawn. Your app balance is ${1}".format(amount, total))

def balance():
    print("Your real balance is ${0}".format(total))


w = 30
print("Ross withdraws $", w)
withdraw(w)
balance()

d = 50
print("Ross deposits $", d)
deposit(50)
balance()

w = 150
print("Ross withdraws $", w)
withdraw(w)
balance()

banking.R

# Ross is a programmer for Megabank, working on a new smartphone app that
# helps users transfer money between accounts. He's relatively new to R,
# the language preferred by the top brass, and is not entirely sure of
# the difference between all the operators available for assigning
# values to variables. Specifically, there's this "scoped assignment" thing
# that sure looks like a harpoon to Ross. What's it for?

# Ross opens a bank account, then uses the app to perform a series of
# transactions. Because he's no fool, he does so in the lobby of a
# Megabank branch, and the bank teller informs him after each step what
# his balance is. If everything is working correctly, Ross should be able
# to take back out exactly what he put in... unless the app is not working!

scoped <- FALSE

open.account <- function(total) {
  list(
    deposit = function(amount) {
      if(amount <= 0)
        stop("Deposits must be positive!\n")
      if (scoped)
         total <<- total + amount
      else
        total <- total + amount
      cat(amount, "deposited.  Your balance is $", total, "in the app.\n\n")
    },
    withdraw = function(amount) {
      if(amount > total)
        stop("You don't have that much money!\n")
      if (scoped)
        total <<- total - amount
      else
        total <- total - amount
      cat(amount, "withdrawn.  Your balance is $", total, "\n\n")
    },
    balance = function() {
      cat("Your balance is $", total, "in reality\n\n")
    }
  )
}

x <- 130
cat("Ross opens a new account with $", x, "\n")
ross <- open.account(x)

w <- 30
cat("Ross withdraws $", w, "\n")
ross$withdraw(w)
ross$balance()

d <- 50
cat("Ross deposits $", d, "\n")
ross$deposit(50)
ross$balance()

w <- 150
cat("Ross withdraws $", w, "\n")
ross$withdraw(w)

ross$balance()