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)

• asteri: Thanks for your feedback. What do you mean by "Try to use Python 3?" Which feature or design consideration were you referring to that looked like an earlier version?
• tokland: print is not a statement anymore, it's a function, so I concluded you are using Python2.
• asteri: Got it, thanks. One more question. I'm used to for... in... logic iterating over each element in a set. I just want to fully understand what's happening in for guess_iteration in count(1). I get that guess_iteration is being incremented each time the loop runs, but is count(1) kind of a hacky "while(true)" sort of thing? Or is the count() function specifically made for infinite loops that you have to break out of?
• tokland: yes, with count you avoid the verbose while+counter (I wouldn't call a hack, I think it's way better because is more declarative). How it works: count(n) returns a iterator, check docs.python.org/2/library/itertools.html#itertools.count and stackoverflow.com/questions/19151/build-a-basic-python-iterator. Regarding the last question, count is a basic functional abstraction, an infinite lazy counter that comes handy in a lot of situations.

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)

• Sᴀᴍ Onᴇᴌᴀ: Welcome to Code Review! Could you please edit your answer and explain what benefit this would have?