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 = '''
amtunititem
24slicesbaguette
2+tbspolive oil
1cuptomatoes
1jarpesto
''' # 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 [[https://wiki.python.org/moin/SimplePrograms?action=recall&rev=154|previous version of this page]]. ---- CategoryDocumentation