Here are some example simple programs. Please feel free to contribute, but see notice at bottom, please.

These examples assume version 2.4 or above of Python.

1 line: Output

print 'hello world'

2 lines: Looping

for name in ['peter', 'paul', 'mary']:
    print name

3 lines: Input, comments

# This is a Python comment. \n is a newline
name = raw_input('What is your name?\n')
print 'Hi', name

3 lines: Builtin enumerate function

my_list = ['john', 'pat', 'gary', 'michael']
for i, name in enumerate(my_list):
    print "iteration %i is %s" % (i, name)

4 lines: Fibonacci, tuple assignment

parents, babies = (1, 1)
while babies < 100:
    print 'This generation has %d babies' % babies
    parents, babies = (babies, parents + babies)

5 lines: Functions

def greet(name):
    print 'hello', name
greet('Jack')
greet('Jill')
greet('Bob')

6 lines: Import, regular expressions

import re
for test_string in ['555-1212', 'ILL-EGAL']:
    if re.match(r'^\d{3}-\d{4}$', test_string):
        print test_string, 'is a valid US local phone number'
    else:
        print test_string, 'rejected'

7 lines: Dictionaries, generator expressions

prices = {'apple': 0.40, 'banana': 0.50}
my_purchase = {
    'apple': 1,
    'banana': 6}
grocery_bill = sum(prices[fruit] * my_purchase[fruit]
                   for fruit in my_purchase)
print 'I owe the grocer $%.2f' % grocery_bill

8 lines: Command line arguments, exception handling

# This program adds up integers in the command line
import sys
try:
    total = sum(int(arg) for arg in sys.argv[1:])
    print 'sum =', total
except ValueError:
    print 'Please supply integer arguments'

9 lines: Opening files

# indent your Python code to put into an email
import glob
# glob supports Unix style pathname extensions
python_files = glob.glob('*.py')
for fn in sorted(python_files):
    print '    ------'
    for line in open(fn):
        print '    ' + line.rstrip()
    print

10 lines: Time, conditionals

import time
now = time.localtime()
hour = now.tm_hour
if hour < 8: print 'sleeping'
elif hour < 9: print 'commuting'
elif hour < 17: print 'working'
elif hour < 18: print 'commuting'
elif hour < 20: print 'eating'
elif hour < 22: print 'resting'
else: print 'sleeping'

11 lines: Triple-quoted strings, while loop

REFRAIN = '''
%d bottles of beer on the wall,
%d bottles of beer,
take one down, pass it around,
%d bottles of beer on the wall!
'''
bottles_of_beer = 99
while bottles_of_beer > 1:
    print REFRAIN % (bottles_of_beer, bottles_of_beer,
        bottles_of_beer - 1)
    bottles_of_beer -= 1

12 lines: Unit testing with unittest

def add_money(amounts):
    # do arithmetic in pennies so as not to accumulate float errors
    pennies = sum([round(int(amount * 100)) for amount in amounts])
    return float(pennies / 100.0)
if __name__ == '__main__':
    import unittest
    class TestAddMoney(unittest.TestCase):
        def test_float_errors(self):
            self.failUnlessEqual(add_money([0.13, 0.02]), 0.15)
            self.failUnlessEqual(add_money([100.01, 99.99]), 200)
            self.failUnlessEqual(add_money([0, -13.00, 13.00]), 0)
    unittest.main()

13 lines: Doctest-based unit testing

# Same as above but including doctest-based tests.
def add_money(amounts):
    """ do arithmetic in pennies so as not to accumulate float errors
    >>> assert add_money([0.13, 0.02]) == 0.15
    >>> assert add_money([100.01, 99.99]) == 200
    >>> assert add_money([0, -13.00, 13.00]) == 0

    """
    pennies = sum([round(int(amount * 100)) for amount in amounts])
    return float(pennies / 100.0)
if __name__ == '__main__':
    import doctest
    doctest.testmod()

14 lines: Classes

class BankAccount:
    def __init__(self, initial_balance=0):
        self.balance = initial_balance
    def deposit(self, amount):
        self.balance += amount
    def withdraw(self, amount):
        self.balance -= amount
    def overdrawn(self):
        return self.balance < 0
my_account = BankAccount()
my_account.deposit(15)
my_account.withdraw(5)
print my_account.balance
print my_account.overdrawn()

15 lines: itertools

import itertools
lines = '''
This is the
first paragraph.

This is the second.
'''.splitlines()
# Use itertools.groupby and bool to return groups of
# consecutive lines that either have content or don't.
for has_chars, frags in itertools.groupby(lines, bool):
    if has_chars:
        print ' '.join(frags)
# PRINTS:
# This is the first paragraph.
# This is the second.

18 lines: 8-Queens Problem (recursion)

BOARD_SIZE = 8

def under_attack(col, queens):
    left = right = col
    for r, c in reversed(queens):
        left, right = left-1, right+1
        if c in (left, col, right):
            return True
    return False

def solve(n):
    if n == 0: return [[]]
    smaller_solutions = solve(n-1)
    return [solution+[(n,i+1)]
        for i in range(BOARD_SIZE)
            for solution in smaller_solutions
                if not under_attack(i+1, solution)]
for answer in solve(BOARD_SIZE): print answer

20 lines: Prime numbers sieve w/fancy generators

import itertools

def iter_primes():
     # an iterator of all numbers between 2 and +infinity
     numbers = itertools.count(2)

     # generate primes forever
     while True:
         # generate the first number from the iterator,
         # which should always be a prime
         prime = numbers.next()
         yield prime

         # ponder this code for a bit, it will blow your
         # mind, it's recursively setting up a chain of filters
         numbers = itertools.ifilter(prime.__rmod__, numbers)

for p in iter_primes():
    if p > 1000: break
    print p

28 lines: 8-Queens Problem (define your own exceptions)

BOARD_SIZE = 8

class BailOut(Exception):
    pass

def validate(queens):
    left = right = col = queens[-1]
    for r in reversed(queens[:-1]):
        left, right = left-1, right+1
        if r in (left, col, right):
            raise BailOut

def add_queen(queens):
    for i in range(BOARD_SIZE):
        test_queens = queens + [i]
        try:
            validate(test_queens)
            if len(test_queens) == BOARD_SIZE:
                return test_queens
            else:
                return add_queen(test_queens)
        except BailOut:
            pass
    raise BailOut

queens = add_queen([])
print queens
print "\n".join(". "*q + "Q " + ". "*(BOARD_SIZE-q-1) for q in queens)

30 lines: generator function, list comprehension

def partition_generator(depth, width): # a generator (iterates comb(depth - 1, width - 1))
    def move_col(c):                   # move item left 1 bin
        sv[c-1] += 1
        sv[c] -= 1
    def find_c():                      # find rightmost bin with >1 items
        i = -1
        while i < 0:
            if sv[i] > 1:
                return i
            i -= 1
    def rollover(c):                   # move item and swap bins
        move_col(c)
        sv[-1] = sv[c]
        sv[c] = 1
    if depth < width:                  # must have at least as many bins as items
        print 'depth', depth, 'must be greater than width', width
        return                         # invalid depth, terminate generator
    max_element = depth - width + 1    # largest amount held by a bin
    sv = [1 for i in range(width)]     # list comprehension: init all bins to 1
    sv[-1] = max_element               # start with max_element in right bin
    yield sv                           # this initial condition is 1st partition
    while sv[0] < max_element:         # terminate when all moveable items in leftmost bin
        c = find_c()                   # find rightmost bin that has a moveable item
        if c < -1:                     # if not THE rightmost bin, rollover
            rollover(c)
            yield sv                   # and return as next partition
        else:                          # otherwise, just need to move item
            move_col(c)
            yield sv                   # and return as next partition
for p in partition_generator(6, 4): print p

Hi, I started this page in May 2007, and I provided the first 10+ or so examples (which may have changed since then). -- SteveHowell

All code on this page is open source, of course, with the standard Python license.

Minor cleanups are welcome, but if you want to do major restructuring of this page, please run them by the folks on the Python mailing list, or if you are impatient for a response, please just make your own copy of this page. Thanks, and I hope this code is useful for you!

Some goals for this page:

• 1) All examples should be simple. 2) There should be a gentle progression through Python concepts.

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