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These Python examples follow the convention that each program gets one line longer than the one before it. Please try to maintain this convention. I also try to introduce at least one new feature in each program. {{{ |
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 print 'hello world' }}} ------ 2 lines: Input, assignment, comments {{{#!python name = raw_input('What is your name?\n') # \n is a newline print 'Hi', name }}} ------ 3 lines: For loop, builtin 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 parents, babies = (1, 1) while babies < 100: print 'This generation has %d babies' % babies 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() }}} ------ 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) }}} |
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print 'hello world' ------ for name in ('peter', 'paul', 'mary'): print name ------ # This is a Python comment. \n is a newline name = raw_input('What is your name?\n') print 'Hi', name ------ parent_rabbits, baby_rabbits = (1, 1) while baby_rabbits < 100: print 'This generation has %d rabbits' % baby_rabbits parent_rabbits, baby_rabbits = (baby_rabbits, parent_rabbits + baby_rabbits) ------ # def defines a method in Python def tax(item_charge, g = 0.05): return item_charge * g print '%.2f' % tax(11.35) print '%.2f' % tax(40.00, 0.08) ------ import re for test_string in [ '555-1212', 'ILL-EGAL']: if re.match('\d\d\d-\d\d\d\d$', test_string): print test_string, 'is a valid US local phone number' else: print test_string, 'rejected' ------ 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 ------ #!/usr/local/bin/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: print 'Please supply integer arguments' ------ # indent your Python code to put into an email import glob python_files = glob.glob('*.py') python_files.sort() for fn in python_files: print ' ------' for line in open(fn): print ' ' + line.rstrip() ------ 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' }}} |
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' }}} ---- CategoryLanguage |
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
3 lines: For loop, builtin enumerate function
4 lines: Fibonacci, tuple assignment
5 lines: Functions
6 lines: Import, regular expressions
7 lines: Dictionaries, generator expressions
8 lines: Command line arguments, exception handling
9 lines: Opening files
10 lines: Time, conditionals
11 lines: Triple-quoted strings, while loop
12 lines: Classes
1 class BankAccount(object):
2 def __init__(self, initial_balance=0):
3 self.balance = initial_balance
4 def deposit(self, amount):
5 self.balance += amount
6 def withdraw(self, amount):
7 self.balance -= amount
8 def overdrawn(self):
9 return self.balance < 0
10 my_account = BankAccount(15)
11 my_account.withdraw(5)
12 print my_account.balance
13 lines: Unit testing with unittest
1 import unittest
2 def median(pool):
3 copy = sorted(pool)
4 size = len(copy)
5 if size % 2 == 1:
6 return copy[(size - 1) / 2]
7 else:
8 return (copy[size/2 - 1] + copy[size/2]) / 2
9 class TestMedian(unittest.TestCase):
10 def testMedian(self):
11 self.failUnlessEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7)
12 if __name__ == '__main__':
13 unittest.main()
14 lines: Doctest-based testing
1 def median(pool):
2 '''Statistical median to demonstrate doctest.
3 >>> median([2, 9, 9, 7, 9, 2, 4, 5, 8])
4 7
5 '''
6 copy = sorted(pool)
7 size = len(copy)
8 if size % 2 == 1:
9 return copy[(size - 1) / 2]
10 else:
11 return (copy[size/2 - 1] + copy[size/2]) / 2
12 if __name__ == '__main__':
13 import doctest
14 doctest.testmod()
15 lines: itertools
1 import itertools
2 lines = '''
3 This is the
4 first paragraph.
5
6 This is the second.
7 '''.splitlines()
8 # Use itertools.groupby and bool to return groups of
9 # consecutive lines that either have content or don't.
10 for has_chars, frags in itertools.groupby(lines, bool):
11 if has_chars:
12 print ' '.join(frags)
13 # PRINTS:
14 # This is the first paragraph.
15 # This is the second.
16 lines: csv module, tuple unpacking, cmp() built-in
1 import csv
2
3 # write stocks data as comma-separated values
4 writer = csv.writer(open('stocks.csv', 'wb'))
5 writer.writerows([
6 ('GOOG', 'Google, Inc.', 505.24, 0.47, 0.09),
7 ('YHOO', 'Yahoo! Inc.', 27.38, 0.33, 1.22),
8 ('CNET', 'CNET Networks, Inc.', 8.62, -0.13, -1.49)
9 ])
10
11 # read stocks data, print status messages
12 stocks = csv.reader(open('stocks.csv', 'rb'))
13 status_labels = {-1: 'down', 0: 'unchanged', 1: 'up'}
14 for ticker, name, price, change, pct in stocks:
15 status = status_labels[cmp(float(change), 0.0)]
16 print '%s is %s (%s%%)' % (name, status, pct)
18 lines: 8-Queens Problem (recursion)
1 BOARD_SIZE = 8
2
3 def under_attack(col, queens):
4 left = right = col
5 for r, c in reversed(queens):
6 left, right = left-1, right+1
7 if c in (left, col, right):
8 return True
9 return False
10
11 def solve(n):
12 if n == 0: return [[]]
13 smaller_solutions = solve(n-1)
14 return [solution+[(n,i+1)]
15 for i in range(BOARD_SIZE)
16 for solution in smaller_solutions
17 if not under_attack(i+1, solution)]
18 for answer in solve(BOARD_SIZE): print answer
20 lines: Prime numbers sieve w/fancy generators
1 import itertools
2
3 def iter_primes():
4 # an iterator of all numbers between 2 and +infinity
5 numbers = itertools.count(2)
6
7 # generate primes forever
8 while True:
9 # get the first number from the iterator (always a prime)
10 prime = numbers.next()
11 yield prime
12
13 # this code iteratively builds up a chain of
14 # filters...slightly tricky, but ponder it a bit
15 numbers = itertools.ifilter(prime.__rmod__, numbers)
16
17 for p in iter_primes():
18 if p > 1000:
19 break
20 print p
21 lines: XML/HTML parsing (using Python 2.5 or third-party library)
1 dinner_recipe = '''<html><body><table>
2 <tr><th>amt</th><th>unit</th><th>item</th></tr>
3 <tr><td>24</td><td>slices</td><td>baguette</td></tr>
4 <tr><td>2+</td><td>tbsp</td><td>olive oil</td></tr>
5 <tr><td>1</td><td>cup</td><td>tomatoes</td></tr>
6 <tr><td>1</td><td>jar</td><td>pesto</td></tr>
7 </table></body></html>'''
8
9 # In Python 2.5 or from http://effbot.org/zone/element-index.htm
10 import xml.etree.ElementTree as etree
11 tree = etree.fromstring(dinner_recipe)
12
13 # For invalid HTML use http://effbot.org/zone/element-soup.htm
14 # import ElementSoup, StringIO
15 # tree = ElementSoup.parse(StringIO.StringIO(dinner_recipe))
16
17 pantry = set(['olive oil', 'pesto'])
18 for ingredient in tree.getiterator('tr'):
19 amt, unit, item = ingredient
20 if item.tag == "td" and item.text not in pantry:
21 print "%s: %s %s" % (item.text, amt.text, unit.text)
28 lines: 8-Queens Problem (define your own exceptions)
1 BOARD_SIZE = 8
2
3 class BailOut(Exception):
4 pass
5
6 def validate(queens):
7 left = right = col = queens[-1]
8 for r in reversed(queens[:-1]):
9 left, right = left-1, right+1
10 if r in (left, col, right):
11 raise BailOut
12
13 def add_queen(queens):
14 for i in range(BOARD_SIZE):
15 test_queens = queens + [i]
16 try:
17 validate(test_queens)
18 if len(test_queens) == BOARD_SIZE:
19 return test_queens
20 else:
21 return add_queen(test_queens)
22 except BailOut:
23 pass
24 raise BailOut
25
26 queens = add_queen([])
27 print queens
28 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
1 def partition_generator(depth, width): # a generator (iterates comb(depth - 1, width - 1))
2 def move_col(c): # move item left 1 bin
3 sv[c-1] += 1
4 sv[c] -= 1
5 def find_c(): # find rightmost bin with >1 items
6 i = -1
7 while i < 0:
8 if sv[i] > 1:
9 return i
10 i -= 1
11 def rollover(c): # move item and swap bins
12 move_col(c)
13 sv[-1] = sv[c]
14 sv[c] = 1
15 if depth < width: # must have at least as many bins as items
16 print 'depth', depth, 'must be greater than width', width
17 return # invalid depth, terminate generator
18 max_element = depth - width + 1 # largest amount held by a bin
19 sv = [1 for i in range(width)] # list comprehension: init all bins to 1
20 sv[-1] = max_element # start with max_element in right bin
21 yield sv # this initial condition is 1st partition
22 while sv[0] < max_element: # terminate when all moveable items in leftmost bin
23 c = find_c() # find rightmost bin that has a moveable item
24 if c < -1: # if not THE rightmost bin, rollover
25 rollover(c)
26 yield sv # and return as next partition
27 else: # otherwise, just need to move item
28 move_col(c)
29 yield sv # and return as next partition
30 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