Apple picking game. More efficient method than using global variables

Question

I have been working on a small game called apple picker, it's text-based, and relvolves around picking and selling apples. Unfortunately I've been using global variables for this whole thing and it's starting to get a bit ugly looking. Is there a more efficient way to do this than using global variables?

from random import randint
import console, time
global gold
global apples
apples = 1
gold = 1
prompt = "> "
def main():
 global gold
 global apples
 console.clear()
 print "Gold: %r Apples: %r" % (gold, apples)
 print "Pick an apple?"
 choice = raw_input(prompt)
 if choice == "yes":
 pick()
 elif choice == "no":
 console.clear()
 global gold 
 global apples
 print "Apples: %r Gold: %r" % (apples, gold)
 print "Sell apples?"
 sell = raw_input(prompt)
 if sell == "yes" and apples >= 1:
 global gold
 global apples
 apple_sales = randint(1,5)
 gold = (gold * (apples / 2)) * apple_sales
 apples = apples - apples
 if gold >= 25 ** 25:
 console.clear()
 print "\t\t\tYou won!"
 print "Congrats on controlling the apple market!"
 else: 
 main()
 elif sell == "yes" and apples <= 0:
 print "\nNot enough apples!"
 time.sleep(0.7)
 main()
 elif sell == "no":
 main()
 else: 
 main()
 elif choice == "exit":
 console.clear()
 print "Bye..."
 else: 
 main()
def pick():
 console.clear()
 global gold
 global apples
 print "Type 0 to exit. How many?"
 print "Apples: %r Gold %r" % (apples, gold)
 try: 
 apple_num = int(raw_input(prompt))
 if apple_num == 3 or apple_num == 2 or apple_num == 1:
 global apples
 apples = apples + apple_num
 time.sleep(0.5)
 pick()
 elif apple_num >= 4:
 console.clear()
 print "You can't haul that many apples!"
 time.sleep(0.5)
 pick()
 elif apple_num == 0:
 main()
 except ValueError:
 pick()
main()

Ignore the console module. I wrote this script on IOS.

Answer 1

Store the game data in a class and pass it around. Makes testing individual sections of the game easier.

I simplified some things here or there where I did not understand the logic.

# import console
from random import randint
import time
class EndGame(Exception):
 pass
class GameData(object):
 apples = 1
 gold = 1
 def __str__(self):
 return "Apples: %d Gold: %d" % (self.apples, self.gold)
def clear():
 # console.clear()
 pass
def delay(length):
 time.sleep(length)
def prompt(message):
 show(message)
 choice = raw_input("> ")
 if choice == "exit":
 raise EndGame
 return choice
def show(message):
 if isinstance(message, str):
 print message
 elif isinstance(message, (list, tuple)):
 print "\n".join(message)
def offer_alternatives(data):
 clear()
 show(str(data))
 choice = prompt("Sell apples?")
 if choice == "yes":
 if data.apples >= 1:
 apple_sales = randint(1, data.apples)
 data.gold += apple_sales # not sure what the old logic was doing
 data.apples -= apple_sales
 elif data.apples <= 0:
 show("Not enough apples!")
 delay(0.7)
 return data
def run_game(data):
 keep_going = True
 try:
 while keep_going:
 show(str(data))
 choice = prompt("Pick an apple?")
 if choice == "yes":
 data = pick(data)
 else:
 data = offer_alternatives(data)
 if data.gold >= 25: # 25 ** 25 means 25 raised to the 25.
 clear()
 show(["You won!",
 "Congrats on controlling the apple market!"])
 keep_going = False
 except EndGame:
 show("Bye")
def force_valid_choice(message, type, validator):
 value = None 
 while True:
 choice = prompt(message)
 try:
 value = type(choice)
 except ValueError:
 pass 
 else:
 if validator(value):
 break
 return value
def pick(data):
 clear()
 show(str(data))
 while True:
 choice = force_valid_choice("Type 0 to exit. How many?", int,
 lambda x: x >= 0)
 if choice >= 4:
 clear()
 show("You can't haul that many apples!")
 delay(0.5)
 elif choice == 0:
 return data
 elif choice in (3, 2, 1):
 data.apples += choice
 delay(0.5)
 return data
def main():
 data = GameData()
 run_game(data)
if __name__ == "__main__":
 main()

• Vladimir Putin: Why do you have to do if __name__ == "__main__": when you could just do main()?
• Sean Perry: In the directory where this file is saved you can load it directly in the Python interpreter and experiment with each function. The trick is if you load it as a module no code is run. The 'name' will be 'filename.py' or the like. But if you run the program as "python filename.py" the 'name' is now main and the code under the if is run.
• Sean Perry: Experimenting with the code in the interpreter is a great way to learn and develop code faster. Moving the main under the if also makes it so unittests can be run.
• jonrsharpe: @SeanPerry note that your GameData attributes are class attributes - it's OK in this case, where there will only be one instance at a time, but the user will notice some odd behaviour if, for example, a replay option is added.
• Sean Perry: Agreed @jonrsharpe. I was trying to keep it simple to match the OPs experience in Python.

Answer 2

You don't need to list those as globals. Variables defined at the module-level namespace are available in functions in that module. Just remove the global declarations and you should be fine.

Another thing: calling main() is kind of dangerous. It's always better to do this instead:

if __name__ == '__main__':
 main()

That way main() won't be run when the module is imported.

• Vladimir Putin: I could also just do from file import main. Right?
• whereswalden: You could use from __file__ import main, but that violates the Zen of Python, particularly: "Explicit is better than implicit."

Answer 3

Couldn't send this answer yesterday because the site was down for some reason.

First thing you can fix is to add a guard before calling main(). This is the usual way to do things in Python so that you can import you files without running the code corresponding to main :

if __name__ == "__main__":
 main()

Then, one can see that you are using recursion to emulate loops. It is not quite a good idea in Python because recursion is not that optimised (for various reasons) so you should stick to loops if it doesn't make things more complicated. In your case, it doesn't at all : you can remove calls to main from your main function which becomes :

def main():
 global gold
 global apples
 while True:
 print "Gold: %r Apples: %r" % (gold, apples)
 print "Pick an apple?"
 choice = raw_input(prompt)
 if choice == "yes":
 pick()
 elif choice == "no":
 global gold
 global apples
 print "Apples: %r Gold: %r" % (apples, gold)
 print "Sell apples?"
 sell = raw_input(prompt)
 if sell == "yes" and apples >= 1:
 global gold
 global apples
 apple_sales = randint(1,5)
 gold = (gold * (apples / 2)) * apple_sales
 apples = apples - apples
 if gold >= 25 ** 25:
 print "\t\t\tYou won!"
 print "Congrats on controlling the apple market!"
 return
 elif sell == "yes" and apples <= 0:
 print "\nNot enough apples!"
 time.sleep(0.7)
 elif choice == "exit":
 print "Bye..."
 return

From the pick function, you probably don't need to call main as the loop from the main function should handle things properly.

def pick():
 global gold
 global apples
 print "Type 0 to exit. How many?"
 print "Apples: %r Gold %r" % (apples, gold)
 try:
 apple_num = int(raw_input(prompt))
 if apple_num == 3 or apple_num == 2 or apple_num == 1:
 global apples
 apples = apples + apple_num
 time.sleep(0.5)
 pick()
 elif apple_num >= 4:
 print "You can't haul that many apples!"
 time.sleep(0.5)
 pick()
 except ValueError:
 pick()

We can apply the same kind of arguments to pick calling itself :

def pick():
 global gold
 global apples
 while True:
 print "Type 0 to exit. How many?"
 print "Apples: %r Gold %r" % (apples, gold)
 try:
 apple_num = int(raw_input(prompt))
 if apple_num == 3 or apple_num == 2 or apple_num == 1:
 global apples
 apples = apples + apple_num
 time.sleep(0.5)
 elif apple_num >= 4:
 print "You can't haul that many apples!"
 time.sleep(0.5)
 else:
 return
 except ValueError:
 pass

Then, you do not need to repeat global my_var before each and every use, you can do it once at the beginning of the function and that should be enough.

Also, if apple_num == 3 or apple_num == 2 or apple_num == 1 can be written in a concise way in Python : if apple_num in [3, 2, 1]. But as we are using integers, we can use a even better way :if 1 <= apple_num <= 3`.

Then, you can write apples += apple_nums instead of apples = apples + apple_num.

You can simply write apples = 0 instead of apples = apples - apples.

You should try to avoid writing the same condition twice, it makes things harder to understand/maintain. For instance, you could write :

 sell = raw_input(prompt)
 if sell == "yes":
 if apples >= 1:
 apple_sales = randint(1,5)
 gold = (gold * (apples / 2)) * apple_sales
 apples = 0
 if gold >= 25 ** 25:
 print "\t\t\tYou won!"
 print "Congrats on controlling the apple market!"
 return
 elif apples <= 0:
 print "\nNot enough apples!"
 time.sleep(0.7)

and then, becomes apples is known to be an integer at all time, the second condition will always be true if the first is false : we don't need it. Last details on this : the pythonic way to write if my_int != 0 is if my_int. It applies to apples because it will be a positive-or-null integer. Thus, you can write : if apples

Now, we can actually go into your global issue : your pick function could return the number of picked apple and shouldn't print about the total number of apples and gold.

def main():
 apples = 1
 gold = 1
 while True:
 print "Gold: %r Apples: %r" % (gold, apples)
 print "Pick an apple?"
 choice = raw_input(prompt)
 if choice == "yes":
 apples += pick()
 elif choice == "no":
 print "Apples: %r Gold: %r" % (apples, gold)
 print "Sell apples?"
 sell = raw_input(prompt)
 if sell == "yes":
 if apples:
 apple_sales = randint(1,5)
 gold = (gold * (apples / 2)) * apple_sales
 apples = 0
 if gold >= 25 ** 25:
 print "\t\t\tYou won!"
 print "Congrats on controlling the apple market!"
 return
 else:
 print "\nNot enough apples!"
 time.sleep(0.7)
 elif choice == "exit":
 print "Bye..."
 return
def pick():
 picked_apples = 0
 while True:
 print "Type 0 to exit. How many?"
 print "Picked apples: %r" % (picked_apples)
 try:
 apple_num = int(raw_input(prompt))
 if 1 <= apple_num <= 3:
 picked_apples += apple_num
 time.sleep(0.5)
 elif apple_num >= 4:
 print "You can't haul that many apples!"
 time.sleep(0.5)
 else:
 return picked_apples
 except ValueError:
 pass

Finally, you could make your user interface better by providing the different options:

def main():
 apples = 1
 gold = 1
 while True:
 print "Gold: %r Apples: %r" % (gold, apples)
 print "Action ? (pick/sell/exit)"
 choice = raw_input(prompt)
 if choice == "pick":
 apples += pick()
 elif choice == "sell":
 if apples:
 apple_sales = randint(1,5)
 gold = (gold * (apples / 2)) * apple_sales
 apples = 0
 if gold >= 25 ** 25:
 print "\t\t\tYou won!"
 print "Congrats on controlling the apple market!"
 return
 else:
 print "\nNot enough apples!"
 time.sleep(0.7)
 elif choice == "exit":
 print "Bye..."
 return