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Comment: Warning note that this is Python 2
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Changing code to Python 3 syntax
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Please note that these examples are written in Python 2, and may need some adjustment to run under Python 3. | 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 2 }}} The examples below will increase in number of lines of code and difficulty: |
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{{{ print 'Hello, world!' }}} ---- |
{{{ print ('Hello, world!') }}} ---- |
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{{{ name = raw_input('What is your name?\n') print 'Hi, %s.' % name }}} ---- |
{{{ name = input('What is your name?\n') print ('Hi, %s.' % name) }}} ---- |
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print "iteration {iteration} is {name}".format(iteration=i, name=name) }}} ---- |
print ("iteration {iteration} is {name}".format(iteration=i, name=name)) }}} ---- |
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print 'This generation has {0} babies'.format(babies) | print ('This generation has {0} babies'.format(babies)) |
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print 'Hello', name | print ('Hello', name) |
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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' }}} ---- |
print (test_string, 'rejected') }}} ---- |
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print 'I owe the grocer $%.2f' % grocery_bill }}} ---- |
print ('I owe the grocer $%.2f' % grocery_bill) }}} ---- |
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{{{ #! /usr/bin/env python # This program adds up integers in the command line |
{{{ # 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' }}} ---- |
print ('Please supply integer arguments') }}} ---- |
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print ' ------' + file_name | print (' ------' + file_name) |
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print ' ' + line.rstrip() }}} ---- |
print (' ' + line.rstrip()) print() }}} ---- |
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print activities[activity_time] | print (activities[activity_time]) |
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print 'Unknown, AFK or sleeping!' }}} ---- |
print ('Unknown, AFK or sleeping!') }}} ---- |
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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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my_account.withdraw(5) print my_account.balance }}} ---- |
my_account.withdraw(50) print (my_account.balance, my_account.overdrawn()) }}} ---- |
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return copy[(size - 1) / 2] | return copy[int((size - 1) / 2)] |
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return (copy[size/2 - 1] + copy[size/2]) / 2 | return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2 |
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self.failUnlessEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7) | self.assertEqual(median([2, 9, 9, 7, 9, 2, 4, 5, 8]), 7) |
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7 | 6 #change to 7 in order to pass the test |
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return copy[(size - 1) / 2] | return copy[int((size - 1) / 2)] |
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return (copy[size/2 - 1] + copy[size/2]) / 2 | return (copy[int(size/2 - 1)] + copy[int(size/2)]) / 2 |
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print ' '.join(frags) | print (' '.join(frags)) |
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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', buffering=0)) 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) }}} ---- |
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))) }}} ---- |
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for i in xrange(BOARD_SIZE) | for i in range(BOARD_SIZE) |
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print answer }}} ---- |
print (answer) }}} ---- |
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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 (using Python 2.5 or third-party library) (this example is in Python 2 syntax) |
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---- 28 lines: 8-Queens Problem (define your own exceptions) |
---- 28 lines (this example is in Python 2 syntax): 8-Queens Problem (define your own exceptions) |
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---- 33 lines: "Guess the Number" Game (edited) from http://inventwithpython.com |
---- 33 lines (this example is in Python 2 syntax): "Guess the Number" Game (edited) from http://inventwithpython.com |
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---- [[CategoryDocumentation|CategoryDocumentation]] |
---- CategoryDocumentation |
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 2
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 (using Python 2.5 or third-party library) (this example is in Python 2 syntax)
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 (this example is in Python 2 syntax): 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 (this example is in Python 2 syntax): "Guess the Number" Game (edited) from http://inventwithpython.com
import random guesses_made = 0 name = raw_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(raw_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)