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 name3 lines: Input, comments
# This is a Python comment. \n is a newline
name = raw_input('What is your name?\n')
print 'Hi', name3 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_bill8 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 ' ------', fn
for line in open(fn):
print ' ' + line.rstrip()
print10 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 -= 112 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()
my_account.deposit(15)
my_account.withdraw(5)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]
else:
return (copy[size/2 - 1] + copy[size/2]) / 2
class TestMedian(unittest.TestCase):
def testMedian(self):
self.failUnlessEqual(median(range(9)), 4)
if __name__ == '__main__':
unittest.main()14 lines: Doctest-based testing
def median(pool):
"""Statistical median to demonstrate doctest.
>>> median(range(9))
4
"""
copy = sorted(pool)
size = len(copy)
if size % 2 == 1:
return copy[(size - 1) / 2]
else:
return (copy[size/2 - 1] + copy[size/2]) / 2
if __name__ == '__main__':
import doctest
doctest.testmod()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.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'))
writer.writerows([
('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)
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 answer20 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:
break
print p21 lines: XML/HTML parsing (using Python 2.5 or third-party library)
dinner_recipe = '''<html><body><table>
<tr><th>amt</th><th>unit</th><th>item</th></tr>
<tr><td>24</td><td>slices</td><td>baguette</td></tr>
<tr><td>2+</td><td>tbsp</td><td>olive oil</td></tr>
<tr><td>1</td><td>cup</td><td>tomatoes</td></tr>
<tr><td>1</td><td>jar</td><td>pesto</td></tr>
</table></body></html>'''
# 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)
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)
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.
Examples for discussion
This example was posted to the page, but it was never really discussed on the mailing list. 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, and even with all the comments, it's still not clear what this program does.
- 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