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Comment: typos
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← Revision 155 as of 2019-11-09 23:29:53 ⇥
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Remove Python 2-specific information, leaving a link to previous revision for accessibility
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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. ------ 1 line: Output {{{ print 'hello world' }}} ------ 2 lines: Looping {{{ for name in ['peter', 'paul', 'mary']: print name }}} ------ 3 lines: Input, comments {{{ # This is a Python comment. \n is a newline name = raw_input('What is your name?\n') print 'Hi', name }}} ------ 3 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 |
The examples below will increase in number of lines of code and difficulty: 1 line: Output {{{ print ('Hello, world!') }}} ---- 2 lines: Input, assignment {{{ name = 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 |
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print 'This generation has %d babies' % babies | print ('This generation has {0} babies'.format(babies)) |
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------ 5 lines: Functions |
---- 5 lines: Functions |
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print 'hello', name | print ('Hello', name) |
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------ 6 lines: Import, regular expressions |
---- 6 lines: Import, regular expressions |
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print test_string, 'is a valid US local phone number' | print (test_string, 'is a valid US local phone number') |
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print test_string, 'rejected' }}} ------ 7 lines: Dictionaries, generator expressions |
print (test_string, 'rejected') }}} ---- 7 lines: Dictionaries, generator expressions |
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print 'I owe the grocer $%.2f' % grocery_bill }}} ------ 8 lines: Command line arguments, exception handling {{{ #!/usr/bin/env python # This program adds up integers in the command line |
print ('I owe the grocer $%.2f' % grocery_bill) }}} ---- 8 lines: Command line arguments, exception handling {{{ # This program adds up integers that have been passed as arguments in the command line |
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print 'sum =', total | print ('sum =', total) |
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print 'Please supply integer arguments' }}} ------ 9 lines: Opening files |
print ('Please supply integer arguments') }}} ---- 9 lines: Opening files |
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for fn in sorted(python_files): print ' ------', fn for line in open(fn): print ' ' + line.rstrip() }}} ------ 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 |
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 |
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bottles_of_beer = 99 | bottles_of_beer = 9 |
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print REFRAIN % (bottles_of_beer, bottles_of_beer, bottles_of_beer - 1) |
print (REFRAIN % (bottles_of_beer, bottles_of_beer, bottles_of_beer - 1)) |
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------ 12 lines: Unit testing with unittest {{{ def add_money(amounts): # do arithmetic in pennies so as not to accumulate float errors pennies = sum([round(int(amount * 100)) for amount in amounts]) return float(pennies / 100.0) if __name__ == '__main__': import unittest class TestAddMoney(unittest.TestCase): def test_float_errors(self): self.failUnlessEqual(add_money([0.13, 0.02]), 0.15) self.failUnlessEqual(add_money([100.01, 99.99]), 200) self.failUnlessEqual(add_money([0, -13.00, 13.00]), 0) unittest.main() }}} ------ 13 lines: Doctest-based unit testing {{{ # Same as above but including doctest-based tests. def add_money(amounts): """ do arithmetic in pennies so as not to accumulate float errors >>> assert add_money([0.13, 0.02]) == 0.15 >>> assert add_money([100.01, 99.99]) == 200 >>> assert add_money([0, -13.00, 13.00]) == 0 """ pennies = sum([round(int(amount * 100)) for amount in amounts]) return float(pennies / 100.0) if __name__ == '__main__': import doctest doctest.testmod() }}} ------ 14 lines: Classes {{{ class BankAccount: |
---- 12 lines: Classes {{{ class BankAccount(object): |
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my_account = BankAccount() my_account.deposit(15) my_account.withdraw(5) print my_account.balance print my_account.overdrawn() }}} ------ 15 lines: itertools {{{ import itertools |
my_account = BankAccount(15) my_account.withdraw(50) print (my_account.balance, my_account.overdrawn()) }}} ---- 13 lines: Unit testing with unittest {{{ import unittest def median(pool): copy = sorted(pool) size = len(copy) if size % 2 == 1: return copy[int((size - 1) / 2)] else: return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2 class TestMedian(unittest.TestCase): def testMedian(self): self.assertEqual(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]) 6 #change to 7 in order to pass the test ''' copy = sorted(pool) size = len(copy) if size % 2 == 1: return copy[int((size - 1) / 2)] else: return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2 if __name__ == '__main__': import doctest doctest.testmod() }}} ---- 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): |
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print ' '.join(frags) | print (' '.join(frags)) |
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------ 16 lines: csv module, tuple unpacking, cmp() built-in |
---- 16 lines: csv module, tuple unpacking, cmp() built-in |
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# need to define cmp function in Python 3 def cmp(a, b): return (a > b) - (a < b) |
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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) ]) |
with open('stocks.csv', 'w', newline='') as stocksFileW: writer = csv.writer(stocksFileW) 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, -1.4901] ]) |
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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) |
with open('stocks.csv', 'r') as stocksFile: stocks = csv.reader(stocksFile) 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 (%.2f)' % (name, status, float(pct))) }}} ---- 18 lines: 8-Queens Problem (recursion) |
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left, right = left-1, right+1 | left, right = left - 1, right + 1 |
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if n == 0: return [[]] smaller_solutions = solve(n-1) |
if n == 0: return [[]] smaller_solutions = solve(n - 1) |
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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 |
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prime = numbers.next() | prime = next(numbers) |
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numbers = itertools.ifilter(prime.__rmod__, numbers) | numbers = filter(prime.__rmod__, numbers) |
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print p }}} ------ 21 lines: XML/HTML parsing (using Python 2.5 or third-party library) |
print (p) }}} ---- 21 lines: XML/HTML parsing |
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# In Python 2.5 or from http://effbot.org/zone/element-index.htm | # From http://effbot.org/zone/element-index.htm |
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print "%s: %s %s" % (item.text, amt.text, unit.text) }}} ------ 28 lines: 8-Queens Problem (define your own exceptions) |
print ("%s: %s %s" % (item.text, amt.text, unit.text)) }}} ---- 28 lines: 8-Queens Problem (define your own exceptions) |
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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 }}} ---- CategoryLanguage |
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 = 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(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)) }}} ---- These all run under Python 3. If you are interested in differences between Python 2 and Python 3, please take a look at the [[https://wiki.python.org/moin/SimplePrograms?action=recall&rev=154|previous version of this page]]. ---- CategoryDocumentation |
The examples below will increase in number of lines of code and difficulty:
1 line: Output
print ('Hello, world!')
2 lines: Input, assignment
name = 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 that have been passed as arguments 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 = 9 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(50) print (my_account.balance, my_account.overdrawn())
13 lines: Unit testing with unittest
import unittest def median(pool): copy = sorted(pool) size = len(copy) if size % 2 == 1: return copy[int((size - 1) / 2)] else: return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2 class TestMedian(unittest.TestCase): def testMedian(self): self.assertEqual(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]) 6 #change to 7 in order to pass the test ''' copy = sorted(pool) size = len(copy) if size % 2 == 1: return copy[int((size - 1) / 2)] else: return (copy[int(size/2 - 1)] + copy[int(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 # need to define cmp function in Python 3 def cmp(a, b): return (a > b) - (a < b) # write stocks data as comma-separated values with open('stocks.csv', 'w', newline='') as stocksFileW: writer = csv.writer(stocksFileW) 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, -1.4901] ]) # read stocks data, print status messages with open('stocks.csv', 'r') as stocksFile: stocks = csv.reader(stocksFile) 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 (%.2f)' % (name, status, float(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 (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 = next(numbers) yield prime # this code iteratively builds up a chain of # filters...slightly tricky, but ponder it a bit numbers = filter(prime.__rmod__, numbers) for p in iter_primes(): if p > 1000: break print (p)
21 lines: XML/HTML parsing
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>''' # 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 = 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(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))
These all run under Python 3. If you are interested in differences between Python 2 and Python 3, please take a look at the previous version of this page.