2229
Comment: camelCase method to under_scores
|
10073
generator sieve
|
Deletions are marked like this. | Additions are marked like this. |
Line 1: | Line 1: |
These are 10 small Python programs. Please keep programs ordered by size. {{{ |
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 contribute, but see notice at bottom, please. These examples assume version 2.4 or above of Python. ------ 1 line: Output {{{ print 'hello world' }}} ------ 2 lines: Looping {{{ for name in ['peter', 'paul', 'mary']: print name }}} ------ 3 lines: Input, comments {{{ # This is a Python comment. \n is a newline name = raw_input('What is your name?\n') print 'Hi', name }}} ------ 3 lines: Builtin enumerate function {{{ myList = ['john', 'pat', 'gary', 'michael'] for name in enumerate(myList): print "iteration %i is %s" % (name[0], name[1]) }}} ------ 4 lines: Fibonacci, tuple assignment {{{ parents, babies = (1, 1) while babies < 100: print 'This generation has %d babies' % 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 {{{ #!/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 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 fn in sorted(python_files): print ' ------' for line in open(fn): print ' ' + line.rstrip() }}} ------ 10 lines: 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 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 = 99 while bottles_of_beer > 1: print REFRAIN % (bottles_of_beer, bottles_of_beer, bottles_of_beer - 1) bottles_of_beer -= 1 }}} ------ 12 lines: 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 lines: 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() }}} ------ 13 lines: Doctest-based unit testing {{{ # Same as above but including doctest-based tests. def add_money(amounts): """ do arithmetic in pennies so as not to accumulate float errors >>> assert add_money([0.13, 0.02]) == 0.15 >>> assert add_money([100.01, 99.99]) == 200 >>> assert add_money([0, -13.00, 13.00]) == 0 """ pennies = sum([round(int(amount * 100)) for amount in amounts]) return float(pennies / 100.0) if __name__ == '__main__': import doctest doctest.testmod() }}} ------ 14 lines: 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 lines: 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. }}} ------ 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: Sieve revisited, generators {{{ import itertools def iter_primes(): # an iterator of all numbers between 2 and +infinity numbers = itertools.count(2) # generate primes forever while True: # generate the first number from the iterator, # which should always be a prime prime = numbers.next() yield prime # lazily remove all numbers from the iterator that # are divisible by prime we just selected numbers = itertools.ifilter(prime.__rmod__, numbers) for p in iter_primes(): if p > 1000: break print p }}} ------ 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) }}} ------ 30 lines: generator function, list comprehension {{{ def partition_generator(depth, width): # a generator (iterates comb(depth - 1, width - 1)) def move_col(c): # move item left 1 bin sv[c-1] += 1 sv[c] -= 1 def find_c(): # find rightmost bin with >1 items i = -1 while i < 0: if sv[i] > 1: return i i -= 1 def rollover(c): # move item and swap bins move_col(c) sv[-1] = sv[c] sv[c] = 1 if depth < width: # must have at least as many bins as items print 'depth', depth, 'must be greater than width', width return # invalid depth, terminate generator max_element = depth - width + 1 # largest amount held by a bin sv = [1 for i in range(width)] # list comprehension: init all bins to 1 sv[-1] = max_element # start with max_element in right bin yield sv # this initial condition is 1st partition while sv[0] < max_element: # terminate when all moveable items in leftmost bin c = find_c() # find rightmost bin that has a moveable item if c < -1: # if not THE rightmost bin, rollover rollover(c) yield sv # and return as next partition else: # otherwise, just need to move item move_col(c) yield sv # and return as next partition for p in partition_generator(6, 4): print p }}} |
Line 5: | Line 326: |
print 'hello world' ------ for name in ('peter', 'paul', 'mary'): print name ------ # This is a Python comment. \n is a newline name = raw_input('What is your name?\n') print 'Hi', name ------ 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) ------ # def defines a method in Python def tax(item_charge, g = 0.05): return item_charge * g print '%.2f' % tax(11.35) print '%.2f' % tax(40.00, 0.08) ------ 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' ------ 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 ------ class ShoppingCart: def __init__(self): self.items = [] def buy(self, item): self.items.append(item) def bought_items(self): return self.items my_cart = ShoppingCart() my_cart.buy('apple') my_cart.buy('banana') print my_cart.bought_items() ------ # 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() ------ 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' }}} |
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. ---- CategoryLanguage |
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 contribute, but see notice at bottom, please.
These examples assume version 2.4 or above of Python.
1 line: Output
print 'hello world'
2 lines: Looping
for name in ['peter', 'paul', 'mary']: print name
3 lines: Input, comments
# This is a Python comment. \n is a newline name = raw_input('What is your name?\n') print 'Hi', name
3 lines: Builtin enumerate function
myList = ['john', 'pat', 'gary', 'michael'] for name in enumerate(myList): print "iteration %i is %s" % (name[0], name[1])
4 lines: Fibonacci, tuple assignment
parents, babies = (1, 1) while babies < 100: print 'This generation has %d babies' % 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 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 fn in sorted(python_files): print ' ------' for line in open(fn): print ' ' + line.rstrip() print
10 lines: 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 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 = 99 while bottles_of_beer > 1: print REFRAIN % (bottles_of_beer, bottles_of_beer, bottles_of_beer - 1) bottles_of_beer -= 1
12 lines: 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 lines: 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()
13 lines: Doctest-based unit testing
# Same as above but including doctest-based tests. def add_money(amounts): """ do arithmetic in pennies so as not to accumulate float errors >>> assert add_money([0.13, 0.02]) == 0.15 >>> assert add_money([100.01, 99.99]) == 200 >>> assert add_money([0, -13.00, 13.00]) == 0 """ pennies = sum([round(int(amount * 100)) for amount in amounts]) return float(pennies / 100.0) if __name__ == '__main__': import doctest doctest.testmod()
14 lines: 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 lines: 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.
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: Sieve revisited, generators
import itertools def iter_primes(): # an iterator of all numbers between 2 and +infinity numbers = itertools.count(2) # generate primes forever while True: # generate the first number from the iterator, # which should always be a prime prime = numbers.next() yield prime # lazily remove all numbers from the iterator that # are divisible by prime we just selected numbers = itertools.ifilter(prime.__rmod__, numbers) for p in iter_primes(): if p > 1000: break print p
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)
30 lines: generator function, list comprehension
def partition_generator(depth, width): # a generator (iterates comb(depth - 1, width - 1)) def move_col(c): # move item left 1 bin sv[c-1] += 1 sv[c] -= 1 def find_c(): # find rightmost bin with >1 items i = -1 while i < 0: if sv[i] > 1: return i i -= 1 def rollover(c): # move item and swap bins move_col(c) sv[-1] = sv[c] sv[c] = 1 if depth < width: # must have at least as many bins as items print 'depth', depth, 'must be greater than width', width return # invalid depth, terminate generator max_element = depth - width + 1 # largest amount held by a bin sv = [1 for i in range(width)] # list comprehension: init all bins to 1 sv[-1] = max_element # start with max_element in right bin yield sv # this initial condition is 1st partition while sv[0] < max_element: # terminate when all moveable items in leftmost bin c = find_c() # find rightmost bin that has a moveable item if c < -1: # if not THE rightmost bin, rollover rollover(c) yield sv # and return as next partition else: # otherwise, just need to move item move_col(c) yield sv # and return as next partition for p in partition_generator(6, 4): print p
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.