Revision 67 as of 2007-06-21 16:16:42

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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. You should be able to run them simply by copying/pasting the code into a file and running Python. Or by inserting this line (#!/bin/env python) at the beginning of your file (Unix/Linux), making the file executable (chmod u+x and running it (./

1 line: Output

print 'hello world'

2 lines: Input, assignment, comments

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

3 lines: For loop, 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: Truth

for value in [True, False, 1, 0, 'foo', '', [0], [], (0,), (), {'a':1}, {}, None]:
    if value:
        print repr(value), 'evaluates to True'
        print repr(value), 'evaluates to False'

/!\ Edit conflict - other version:

5 lines: Truth

for value in [True, False, 1, 0, 'foo', '', [0], [], (0,), (), {'a':1}, {}, None]:
    if value:
        print repr(value), 'evaluates to True'
        print repr(value), 'evaluates to False'

/!\ Edit conflict - your version:

/!\ End of edit conflict

5 lines: Functions

def greet(name):
    print 'hello', name

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'
        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
    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 '    ------', fn
    for line in open(fn):
        print '    ' + line.rstrip()

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

%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: Classes

class BankAccount(object):
    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(15)
print my_account.balance

13 lines: Unit testing with unittest

import unittest
def median(pool):
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[(size - 1) / 2]
        return (copy[size/2 - 1] + copy[size/2]) / 2
class TestMedian(unittest.TestCase):
    def testMedian(self):
        self.failUnlessEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7)
if __name__ == '__main__':

14 lines: Doctest-based testing

def median(pool):
    '''Statistical median to demonstrate doctest.
    >>> median([2, 9, 9, 7, 9, 2, 4, 5, 8])
    copy = sorted(pool)
    size = len(copy)
    if size % 2 == 1:
        return copy[(size - 1) / 2]
        return (copy[size/2 - 1] + copy[size/2]) / 2
if __name__ == '__main__':
    import doctest

15 lines: itertools

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

This is the second.
# 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)
# This is the first paragraph.
# This is the second.

16 lines: csv module, tuple unpacking, cmp() built-in

import csv

# write stocks data as comma-separated values
writer = csv.writer(open('stocks.csv', 'wb'))
    ('GOOG', 'Google, Inc.', 505.24, 0.47, 0.09),
    ('YHOO', 'Yahoo! Inc.', 27.38, 0.33, 1.22),
    ('CNET', 'CNET Networks, Inc.', 8.62, -0.13, -1.49)

# read stocks data, print status messages
stocks = csv.reader(open('stocks.csv', 'rb'))
status_labels = {-1: 'down', 0: 'unchanged', 1: 'up'}
for ticker, name, price, change, pct in stocks:
    status = status_labels[cmp(float(change), 0.0)]
    print '%s is %s (%s%%)' % (name, status, pct)

18 lines: 8-Queens Problem (recursion)


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:
         # get the first number from the iterator (always a prime)
         prime =
         yield prime

         # this code iteratively builds up a chain of
         # filters...slightly tricky, but ponder it a bit
         numbers = itertools.ifilter(prime.__rmod__, numbers)

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

21 lines: XML/HTML parsing (using Python 2.5 or third-party library)

dinner_recipe = '''<html><body><table>
<tr><td>2+</td><td>tbsp</td><td>olive oil</td></tr>

# In Python 2.5 or from
import xml.etree.ElementTree as etree
tree = etree.fromstring(dinner_recipe)

# For invalid HTML use
# import ElementSoup, StringIO
# tree = ElementSoup.parse(StringIO.StringIO(dinner_recipe))

pantry = set(['olive oil', 'pesto'])
for ingredient in tree.getiterator('tr'):
    amt, unit, item = ingredient
    if item.tag == "td" and item.text not in pantry:
        print "%s: %s %s" % (item.text, amt.text, unit.text)

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


class BailOut(Exception):

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]
            if len(test_queens) == BOARD_SIZE:
                return test_queens
                return add_queen(test_queens)
        except BailOut:
    raise BailOut

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

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:

Examples for discussion

This example was posted to the page, but it was never really discussed on the mailing list.

What mailing list? I tried to start a discussion on comp.lang.python. You do realize your posts end up there, don't you? I would have posted this there but apparently you don't check the newsgroup for followups, that explains why you ignored my questions.

I don't think it adds much to the page above. Since this example was posted, I think there have been smaller examples added that demonstrate the same concepts,

At the time I posted it, I didn't see anyone using list comprehension or generator functions.

and even with all the comments, it's still not clear what this program does.

Well, I would have added more, but you're foolishly counting ALL lines instead of executable lines. It's not at all clear what ANY of those examples do since few of them have ANY commentary. You should re-think that. It's a Partition Generator that creates all partitions of Detph items into Width bins such that each bin contains at least one item. It has practical applications, unlike certain other of the examples.


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
        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
            yield sv                   # and return as next partition
        else:                          # otherwise, just need to move item
            yield sv                   # and return as next partition
for p in partition_generator(6, 4): print p


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