Please note that these examples were changed to run under Python 3. The Python2orPython3 page provides advice on how to decide which one will best suit your needs.
Some differences from Python 2 to Python 3:
# Python 2 syntax
print 'Hello, world!'
raw_input('What is your name?\n')
self.failUnlessEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7) # Unit testing with unittest
copy[(size - 1) / 2] # access of a list index without casting to int
xrange(BOARD_SIZE) # xrange exists
cmp(1.0, 0.0) # cmp function exists
iteratable.next() # list iteration
itertools.ifilter(prime.__rmod__, iteratable) # itertools.ifilter is filter in Python 3
# Python 3 syntax
print('Hello, World!')
input('What is your name?\n')
self.assertEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7) # Unit testing with unittest, failUnlessEqual deprecated
copy[int((size - 1) / 2)] # access of a list index needs casting to int
range(BOARD_SIZE) # xrange was renamed to range in Python 3
#cmp needs to be implemented!
def cmp(a, b):
return (a > b) - (a < b)
next(iteratable) # list iteration
filter(prime.__rmod__, iteratable) # is itertools.ifilter in Python 2The 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 -= 112 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))