What do people think about renaming this page to be Python By Immersion? That's really what I think was striving for. It's the analogy to spoken languages, of course.

Here are some example simple programs. Please feel free to contibute, but see notice at bottom, please.

These examples assume version 2.4 or above of Python.

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 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 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
    # glob supports Unix style pathname extensions
    python_files = glob.glob('*.py')
    for fn in sorted(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!
    '''
    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):
        # calculate prime numbers using simple algorithm
        i = 0
        while True:
            divisor = candidates[i]
            if divisor * divisor > candidates[-1]:
                return candidates
            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(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()

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()

15 itertools

    import itertools
    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 itertools.groupby(lines, bool):
        if has_chars:
            print ' '.join(frags)
    # PRINTS:
    # This is the first paragraph.
    # This is the second.

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.

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