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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. Also, please see note at the bottom.


{{{
    ------ 1 Output
    print 'hello world'

    ------ 2 Looping
    for name in ['peter', 'paul', 'mary']:
        print name

    ------ 3 Input, comments
    # This is a Python comment. \n is a newline
    name = raw_input('What is your name?\n')
    print 'Hi', name

    ------ 4 Fibonacci, tuple assignment
    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)

    ------ 5 Functions
    def greet(name):
        print 'hello', name
    greet('Jack')
    greet('Jill')
    greet('Bob')

    ------ 6 Import, regular expresssions
    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'

    ------ 7 Dictionaries, generator comprehensions
    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 Command line arguments, exception handling
    #!/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 ValueError:
        print 'Please supply integer arguments'


    ------ 9 Opening files
    # 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()
        print

    ------ 10 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 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!
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
Line 89: Line 178:
    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 List slicing
    def sieve_of_eratosthenes(candidates):
        i = 0
        while True:
            divisor = candidates[i]
            if divisor * divisor > candidates[-1]:
                return candidates
    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
Line 103: Line 340:
                i += 1
            candidates = candidates[:i] + \
                [num for num in candidates[i:]
                    if num % divisor != 0]
    print sieve_of_eratosthenes(range(2,100))

    ------ 13 Unit testing
    # Let's write reusable code, and unit test it.
    def add_money_correctly(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__':
        for test_args, result in (
                ([0.13, 0.02], 0.15),
                ([100.01, 99.99], 200),
                ([0, -13.00, 13.00], 0)):
            if add_money_correctly(test_args) != result:
                print 'test failed'
                break

    ------ 14 Classes
    class BankAccount:
        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()
    my_account.deposit(15)
    my_account.withdraw(5)
    print my_account.balance
    print my_account.overdrawn()

}}}

Hi, my name is Steve Howell, and I started this page in May 2007, and I provided the first 10+ or so examples (which may have changed since then).

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 contact me through 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!
                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

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.


CategoryDocumentation

SimplePrograms (last edited 2019-11-09 23:29:53 by FrancesHocutt)

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