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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): i = 0 while True: divisor = candidates[i] if divisor * divisor > candidates[-1]: return candidates else: 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.