Differences between revisions 134 and 135
Revision 134 as of 2012-01-25 20:52:03
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Editor: EnalIcho
Comment: Updated the examples to agree with PEP 8, use new style formatting and have gotten rid of input() in the guess_numbers example
Revision 135 as of 2012-01-25 20:54:36
Size: 10862
Editor: EnalIcho
Comment: Updated expected version to be > 2.5, as the with statement needs it.
Deletions are marked like this. Additions are marked like this.
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These examples assume version 2.4.0 or above of Python. These examples assume version 2.5 or above of Python.

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

These examples assume version 2.5 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 (#!/usr/bin/env python) at the beginning of your file (Unix/Linux), making the file executable (chmod u+x filename.py) and running it (./filename.py).

1 line: Output

print 'Hello, world!'

2 lines: Input, assignment

name = raw_input('What is your name?\n')
print 'Hi, %s.' % (name)

3 lines: For loop, built-in enumerate function, new style formatting

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

4 lines: Fibonacci, tuple assignment

parents, babies = (1, 1)
while babies < 100:
    print 'This generation has {x} babies'.format(x=babies)
    parents, babies = (babies, parents + babies)

5 lines: Functions

def greet(name):
    print 'Hello {}'.format(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

#!/usr/bin/env python
# This program adds up integers in the command line
import sys
    total = sum(int(arg) for arg in sys.argv[1:])
    print 'sum = {}'.format(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 file_name in sorted(python_files):
    print '    ------{}'.format(file_name)
    with open(file_name) as f:
        for line in f:
            print '    ' + line.rstrip()


10 lines: Time, conditionals, from..import, for..else

from time import localtime

activities = { 8 : 'Sleeping',
              9 : 'Commuting',
              17 : 'Working',
              18 : 'Commuting',
              20 : 'Eating',
              22 : 'Resting' }

time_now = localtime()
hour = time_now.tm_hour

for activity_time in sorted(activities.keys()):
    if hour < activity_time:
        print activities[activity_time]
    print 'Unknown, AFK or 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

from itertools import groupby
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 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', buffering=0))
    ('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 xrange(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 = numbers.next()
         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 http://effbot.org/zone/element-index.htm
import xml.etree.ElementTree as etree
tree = etree.fromstring(dinner_recipe)

# For invalid HTML use http://effbot.org/zone/element-soup.htm
# 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)

33 lines: "Guess the Number" Game (edited) from http://inventwithpython.com

import random

guesses_made = 0

name = raw_input('Hello! What is your name?\n')

number = random.randint(1, 20)
print 'Well, {name}, I am thinking of a number between 1 and 20.'.format(name=name)

while guesses_made < 6:
    guess = int(raw_input('Take a guess: '))

    guesses_made += 1

    if guess < number:
        print 'Your guess is too low.'

    if guess > number:
        print 'Your guess is too high.'

    if guess == number:

if guess == number:
    print 'Good job, {name}! You guessed my number in {guesses} guesses!'.format(name=name, guesses=guesses_made)
    print 'Nope. The number I was thinking of was {number}.format(number=number)

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.


SimplePrograms (last edited 2015-06-13 04:34:34 by SteveHolden)

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