First Python script: number-guessing game with a global variable

Question

This is my first Python script, and I was hoping to get some feedback. I do have one specific question: is the use of global variables considered a bad practice? When I used them below, my programmer's instincts immediately went off as though I was creating a code-smell, mostly because it seems much less elegant than just having a private String myVariable at the top of a Java class. The use of global myVariable to force the scope seemed a bit hacky. But I don't know a single thing about Python except what I wrote below, so I could be way off.

I also realize that the below code is more complex than it needs to be. I know that it could be written in much fewer lines of code by removing function definitions and such (in fact, my first version was only like 15 lines). But I wrote this more complicated version in order to get a handle on some of the basic concepts like sharing variables, returning from functions, etc.

Any tips or glaring style/best-practices issues are appreciated! (I'm a style-Nazi with Java, so please, don't hold back so that I can learn!)

#!/usr/bin/python

from random import randint

# GLOBALS
guesses = 0
the_number = 0

def checkGuess(guess):        
    global the_number

    if guess <= 0:
        return False
    elif guess == the_number:
        return True
    elif guess < the_number:
        print "The number is HIGHER."
    elif guess > the_number:
        print "The number is LOWER."

    return False    

def isValid(guess):
    return len(guess) > 0 and guess.isdigit()        

def getInput():
    global guesses        
    input = ""

    while not isValid(input):
        input = raw_input("(#" + str(guesses) + ") Guess a number: ")
        if not isValid(input):
            print "Please guess an integer!"

    return int(input)           

def runGame(min, max):    
    global guesses
    global the_number

    the_number = randint(min, max)
    guess = 0

    print "I'm thinking of a number between " + str(min) + " and " + str(max) + " ..."

    while not checkGuess(guess):
        guesses = guesses + 1
        guess = getInput()

    print "YOU WON!"

def printTitle():
    print "----------------------"
    print "----- MASTERMIND -----"
    print "----------------------"
    print ""

def main():
    printTitle()
    runGame(1, 100)

main()

Answer 1

Some notes:

• Mutable global state is a bad programming practice. Instead, pass values as arguments so functions are black boxes that take values (as arguments) and return values. If such a function does not perform any side-effect (print to console, write a file, ...), then it's a "pure function". Try to write pure functions whenever possible.

• Conditionals: Don't write a fallback (return False) where some branches get and others don't. Non-overlapping conditionals are more clear.

• Use name_of_variable and name_of_function.

• Try to use Python 3 whenever possible.

I'd write:

from random import randint
from itertools import count

def is_guess_correct(number, guess):
    if guess == number:
        return True
    elif guess < number:
        print("The number is HIGHER.")
        return False
    else:
        print("The number is LOWER.")
        return False

def is_valid_guess(number_string):
    return number_string.isdigit()

def get_number(guess_iteration):
    while 1:
        number_string = input("({0}) Guess a number: ".format(guess_iteration))
        if is_valid_guess(number_string):
            return int(number_string)
        else:
            print("Please enter a valid integer!")

def run_game(nmin, nmax):
    number = randint(nmin, nmax)
    print("I'm thinking of a number between {0} and {1}...".format(nmin, nmax))

    for guess_iteration in count(1):
        guess = get_number(guess_iteration)
        if is_guess_correct(number, guess):
            print("YOU WON!")
            break

if __name__ == '__main__':
    run_game(1, 100)

Answer 2

You can solve anything without globals. If not, you are doing wrong. If you are using globals, the debugging will be a nightmare. In the checkGuess() you can use single ifs instead of elif. The return will terminate the function and after the first 3 check, the last one can't be anything else than grater than the_number. If you want to check a variable not to be null/zero/empty/None, you can use simply the if var: condition. It will be False if var is null/zero/empty/None. In getInput() you can get the first value before the loop. If you get inside the loop and you use an additional if, then there will be 2 useless condition which slow down the app (I know only a little but...).

#!/usr/bin/python
from random import randint


def checkGuess(guess, the_number):
    if guess <= 0:
        return False
    if guess == the_number:
        return True
    if guess < the_number:
        print "The number is HIGHER."
    else:
        print "The number is LOWER."

    return False


def isValid(guess):
    return guess and guess.isdigit()


def getInput(guesses):
    input = raw_input("(#" + str(guesses) + ") Guess a number: ")
    while not isValid(input):
        print "Please guess an integer!"
        input = raw_input("(#" + str(guesses) + ") Guess a number: ")

    return int(input)



def runGame(min, max):
    the_number = randint(min, max)
    guesses = 0
    guess = 0

    print "I'm thinking of a number between " + str(min) + " and " + str(max) + " ..."

    while not checkGuess(guess, the_number):
        guesses += 1
        guess = getInput(guesses)

    print "YOU WON!"


def printTitle():
    print "----------------------"
    print "----- MASTERMIND -----"
    print "----------------------"
    print 


if __name__=='__main__':
    printTitle()
    runGame(1, 100)

Answer 3

Instead of the printTitle function which is less efficient

def printTitle():
  print "----------------------"
  print "----- MASTERMIND -----"
  print "----------------------"
  print ""

Just save the title to a variable and print it out or make a new file and import the variable from it.

title = """
----------------------
----- MASTERMIND -----
----------------------

"""
print(title)