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Revision 104 as of 2009-11-20 16:35:45
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Editor: PaulBoddie
Comment: Revert vandalism.
Revision 151 as of 2015-06-13 04:34:34
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Editor: SteveHolden
Comment: Warning note that this is Python 2
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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 filename.py) and running it (./filename.py).

    ------ 1 line: Output
{{{#!python
Please note that these examples are written in Python 2, and may need some adjustment to run under Python 3.

1 line: Output







{{{
Line 11: Line 15:
    ------ 2 lines: Input, assignment
{{{#!python


----

2 lines: Input, assignment







{{{
Line 14: Line 29:
print 'Hi, ' + name + '.'
}}}

 1. Usually, the `raw_input` function (renamed to `input` in Python 3) will prompt for a user's input on the same line. Writing `\n` will prompt the user on a new line.
 1. The `print` command is a function in Python 3.
 1. Here, we add the strings together. If we did not, and instead wrote

 {{{#!python start=2 numbers=off
 print 'Hi,',name,'.'
 }}}

 we would get

 {{{
 Hi, Jamie .
 }}}

 Notice how there are spaces that we did not ask Python to write? These unasked for spaces occur when using commas to separate strings when using the `print` command. Rather, it may work better visually to use addition as I did in the example.

    ------ 3 lines: For loop, built-in enumerate function
{{{#!python
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
{{{#!python
print 'Hi, %s.' % name
}}}



----

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







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



----

4 lines: Fibonacci, tuple assignment







{{{
Line 44: Line 65:
    print 'This generation has %d babies' % babies     print 'This generation has {0} babies'.format(babies)
Line 48: Line 69:
    ------ 5 lines: Functions
{{{#!python


----

5 lines: Functions







{{{
Line 51: Line 83:
    print 'hello', name     print 'Hello', name
Line 57: Line 89:
    ------ 6 lines: Import, regular expressions
{{{#!python


----

6 lines: Import, regular expressions







{{{
Line 67: Line 110:
    ------ 7 lines: Dictionaries, generator expressions
{{{#!python


----

7 lines: Dictionaries, generator expressions







{{{
Line 79: Line 133:
    ------ 8 lines: Command line arguments, exception handling
{{{#!python
#!/usr/bin/env python

----

8 lines: Command line arguments, exception handling







{{{

#! /usr/bin/env python
Line 92: Line 157:
    ------ 9 lines: Opening files
{{{#!python

----

9 lines: Opening files







{{{
Line 98: Line 173:
for fn in sorted(python_files):
    print ' ------', fn
    for line in open(fn):
        print ' ' + line.rstrip()
for file_name in sorted(python_files):
    print ' ------' + file_name

    with open(file_name) as f:
    
for line in f:
     print ' ' + line.rstrip()
Line 105: Line 183:
    ------ 10 lines: Time, conditionals
{{{#!python
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
{{{#!python


----

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]
        break
else:
    print 'Unknown, AFK or sleeping!'
}}}



----

11 lines: Triple-quoted strings, while loop







{{{
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   ------ 12 lines: Classes
{{{#!python


----

12 lines: Classes







{{{
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    ------ 13 lines: Unit testing with unittest
{{{#!python


----

13 lines: Unit testing with unittest







{{{
Line 168: Line 298:
    ------ 14 lines: Doctest-based testing
{{{#!python

----

14 lines: Doctest-based testing







{{{
Line 186: Line 326:
    ------ 15 lines: itertools
{{{#!python
i
mport itertools


----

15 lines: itertools







{{{
fr
om itertools import groupby
Line 197: Line 348:
for has_chars, frags in itertools.groupby(lines, bool): for has_chars, frags in groupby(lines, bool):
Line 205: Line 356:
    ------ 16 lines: csv module, tuple unpacking, cmp() built-in
{{{#!python


----

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







{{{
Line 224: Line 386:
    ------ 18 lines: 8-Queens Problem (recursion)
{{{#!python



----

18 lines: 8-Queens Problem (recursion)







{{{
Line 230: Line 404:
Line 231: Line 406:
        left, right = left-1, right+1         left, right = left - 1, right + 1
Line 237: Line 413:
    if n == 0: return [[]]
    smaller_solutions = solve(n-1)
    if n == 0:
       
return [[]]

    smaller_solutions = solve(n - 1)
Line 240: Line 419:
        for i in range(BOARD_SIZE)         for i in xrange(BOARD_SIZE)
Line 243: Line 422:
for answer in solve(BOARD_SIZE): print answer
}}}

    ------ 20 lines: Prime numbers sieve w/fancy generators
{{{#!python
for answer in solve(BOARD_SIZE):
   
print answer
}}}



----

20 lines: Prime numbers sieve w/fancy generators







{{{
Line 270: Line 461:
    ------ 21 lines: XML/HTML parsing (using Python 2.5 or third-party library)
{{{#!python


----

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







{{{
Line 295: Line 497:
    ------ 28 lines: 8-Queens Problem (define your own exceptions)
{{{#!python


----

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







{{{
Line 325: Line 538:

}}}

    ------

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.

----
CategoryDocumentation
}}}



----

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, {0}, I am thinking of a number between 1 and 20.'.format(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:
        break

if guess == number:
    print 'Good job, {0}! You guessed my number in {1} guesses!'.format(name, guesses_made)
else:
    print 'Nope. The number I was thinking of was {0}'.format(number)
}}}



----

[[CategoryDocumentation|CategoryDocumentation]]

Please note that these examples are written in Python 2, and may need some adjustment to run under Python 3.

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

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


4 lines: Fibonacci, tuple assignment

parents, babies = (1, 1)
while babies < 100:
    print 'This generation has {0} babies'.format(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 file_name in sorted(python_files):
    print '    ------' + file_name

    with open(file_name) as f:
        for line in f:
            print '    ' + line.rstrip()

    print


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]
        break
else:
    print 'Unknown, AFK or 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: 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)
my_account.withdraw(5)
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]
    else:
        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__':
    unittest.main()


14 lines: Doctest-based testing

def median(pool):
    '''Statistical median to demonstrate doctest.
    >>> median([2, 9, 9, 7, 9, 2, 4, 5, 8])
    7
    '''
    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

from itertools import groupby
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 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', buffering=0))
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 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:
        break
    print p


21 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)


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, {0}, I am thinking of a number between 1 and 20.'.format(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:
        break

if guess == number:
    print 'Good job, {0}! You guessed my number in {1} guesses!'.format(name, guesses_made)
else:
    print 'Nope. The number I was thinking of was {0}'.format(number)


CategoryDocumentation

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

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