Differences between revisions 70 and 71
Revision 70 as of 2007-06-22 14:04:42
Size: 12324
Editor: gate117
Comment:
Revision 71 as of 2007-07-29 20:15:06
Size: 1079
Editor: 196-11-241-97
Comment: Translator please use sepedi language to label heading (e.g send for romela )
Deletions are marked like this. Additions are marked like this.
Line 30: Line 30:
    parents, babies = (babies, parents + babies)
}}}

    ------ 5 lines: Functions
{{{#!python
def greet(name):
    print 'hello', name
greet('Jack')
greet('Jill')
greet('Bob')
}}}

    ------ 6 lines: Import, regular expressions
{{{#!python
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
{{{#!python
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
{{{#!python
#!/usr/bin/env python
# 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
{{{#!python
# 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()
    print
}}}

    ------ 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
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
{{{#!python
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
{{{#!python
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
{{{#!python
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
{{{#!python
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
{{{#!python
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)
{{{#!python
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 answer
}}}

    ------ 20 lines: Prime numbers sieve w/fancy generators
{{{#!python
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)
{{{#!python
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)
{{{#!python
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

'''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
{{{#!python
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
{{{#!python
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'
}}}

    parents, babies = (babies, pa

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

   1 print 'hello world'

2 lines: Input, assignment, comments

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

3 lines: For loop, builtin enumerate function

   1 my_list = ['john', 'pat', 'gary', 'michael']
   2 for i, name in enumerate(my_list):
   3     print "iteration %i is %s" % (i, name)

4 lines: Fibonacci, tuple assignment

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

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