Differences between revisions 69 and 151 (spanning 82 versions)
Revision 69 as of 2007-06-21 19:07:42
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Editor: c-71-197-235-181
Comment: put True/False in discussion section
Revision 151 as of 2015-06-13 04:34:34
Size: 9624
Editor: SteveHolden
Comment: Warning note that this is Python 2
Deletions are marked like this. Additions are marked like this.
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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
{{{
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
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






Line 28: Line 65:
    print 'This generation has %d babies' % babies     print 'This generation has {0} babies'.format(babies)
Line 32: Line 69:
    ------ 5 lines: Functions

----

5 lines: Functions






Line 35: Line 83:
    print 'hello', name     print 'Hello', name
Line 41: Line 89:
    ------ 6 lines: Import, regular expressions

----

6 lines: Import, regular expressions






Line 51: Line 110:
    ------ 7 lines: Dictionaries, generator expressions

----

7 lines: Dictionaries, generator expressions






Line 63: Line 133:
    ------ 8 lines: Command line arguments, exception handling
{{{
#!/usr/bin/env python

----

8 lines: Command line arguments, exception handling







{{{

#! /usr/bin/env python
Line 76: Line 157:
    ------ 9 lines: Opening files
----

9 lines: Opening files






Line 82: 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 89: Line 183:
    ------ 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


----

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






Line 118: Line 242:
   ------ 12 lines: Classes

----

12 lines: Classes






Line 134: Line 269:
    ------ 13 lines: Unit testing with unittest

----

13 lines: Unit testing with unittest






Line 152: Line 298:
    ------ 14 lines: Doctest-based testing
----

14 lines: Doctest-based testing






Line 170: Line 326:
    ------ 15 lines: itertools
{{{
import itertools


----

15 lines: itertools







{{{
from itertools import groupby
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for has_chars, frags in itertools.groupby(lines, bool): for has_chars, frags in groupby(lines, bool):
Line 189: Line 356:
    ------ 16 lines: csv module, tuple unpacking, cmp() built-in

----

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






Line 194: Line 372:
writer = csv.writer(open('stocks.csv', 'wb')) writer = csv.writer(open('stocks.csv', 'wb', buffering=0))
Line 208: Line 386:
    ------ 18 lines: 8-Queens Problem (recursion)


----

18 lines: 8-Queens Problem (recursion)






Line 214: Line 404:
Line 215: Line 406:
        left, right = left-1, right+1         left, right = left - 1, right + 1
Line 221: Line 413:
    if n == 0: return [[]]
    smaller_solutions = solve(n-1)
    if n == 0:
       
return [[]]

    smaller_solutions = solve(n - 1)
Line 224: Line 419:
        for i in range(BOARD_SIZE)         for i in xrange(BOARD_SIZE)
Line 227: Line 422:
for answer in solve(BOARD_SIZE): print answer
}}}

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



----

20 lines: Prime numbers sieve w/fancy generators






Line 254: Line 461:
    ------ 21 lines: XML/HTML parsing (using Python 2.5 or third-party library)

----

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






Line 279: Line 497:
    ------ 28 lines: 8-Queens Problem (define your own exceptions)

----

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






Line 309: 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.

----

Examples for discussion

'''Mensanator, let's agree to disagree. I saw your example on comp.lang.python, but I gently ignored it. Your example was not vetoed, but I also did not see any strong support for it.

It's easy to resolve this conflict. Please clone this page, and you can make it better than mine. I'm leaving your example here for a few days, but I intend to remove it.

Your point about foolishly counting lines is well received, apart from the "foolish" dig. Again, it's easy to fix my foolishness by simply creating your own page. You're welcome to borrow any code that you like from this page. If you think the whole page needs to be better thought, needs more commentary, etc., then that's the perfect reason to create your own version. -- Steve'''

 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
}}}

The program below is more appropriate in a tutorial on truth/falseness IMHO than as an example of a simple program. I'm not saying all the examples above are perfect, but I think this is a little too language-lawyerly for the fifth program. -- Steve


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


----
CategoryLanguage
}}}



----

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 2019-11-09 23:29:53 by FrancesHocutt)

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