Alan Richmond

Number guessing game

The number guessing game incorporates several simple but important elements of elementary programming and is a good candidate for an introductory programming example.

If you’ve seen any programming course, you’ve probably seen the “Hello World” program. In Python it’s: print ("Hello World")This is done to get the student(s) quickly to the point of having successfully installed Python and knowing how to run it. Perhaps here you’ll explain that various editors and IDEs are available (personally, I like Spyder).

And now you can start talking about data types and variables and operations, probably using the Python interpreter as a calculator. Meanwhile the student is straining at the leash – when can we do some programming??? I humbly suggest that the number guessing game is an excellent candidate, especially if you prefer a faster pace than drip-feeding. It incorporates many programming elements in one relatively short program.

This version plays the game for you (so you don’t need to) using binary search. With a range of 1:128 this will take less than log2 128 = 7 guesses. You can experiment by setting ‘binary’ to False or True. See

I think this is a good introductory didactic program for beginners to Python and algorithms. Create a version without the computer making its own guesses (i.e. delete the binary search bits) and have students play the game and challenge them to find the best strategy (hint: how do you search a dictionary or telephone book?) It demonstrates very compactly:

  • int & boolean data types
  • importing libraries
  • arithmetic operations: +, -, //
  • boolean comparisons: <, >
  • simulation with random number generator
  • basic input/output
  • initialization
  • for loop (could also be done with “while not win:”)
  • conditionals
  • binary search
  • counter increments and +=
  • computer gaming/simulation
  • debugging (e.g. make mistakes like put the guess+=1 at end of loop)
[python] # Simulate (or actually play) Guess the Number
# The number lies in a given range. Choose the number in the middle.
# If guess was too high, choose number in middle of lower half,
# if guess was too low, choose number in middle of upper half.
# Halve the appropriate range and repeat unti the number is correct.
# Authour: Alan Richmond,

binary=False # set this to True or False
lonum,hinum=1,128 # range for the number

import random as r

the_num=r.randint(lonum,hinum) # computer chooses a number randomly
print("I’m thinking of a number between",lonum,"and",hinum)


for i in range(lonum,hinum): # repeat this until guess is correct:
# note the int!
# guess=int(input ("What is your guess: ")) # uncomment to actually play
if binary: guess=lo+(hi-lo)//2 # integer division
else: guess=r.randint(lo,hi)
guesses+=1 # add 1 to count of guesses
# check the guessed number
if guess > the_num:
hi=guess # bring down the upper bound
elif guess < the_num:
lo=guess # push up the lower bound
else: break # yay!

print("That took",guesses,"guesses")
#print("That took {0} guesses".format(guesses)) # alternative to previous line

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