Simple Programs – Programmare con Python

Pagina del Wiki ufficiale con esempi di codice di difficoltà crescente (con lievi modifiche)

Numero 1

Output

print("Hello, world!")

Numero 2

Input, assignment

name=input("What is your name? ")
print("Hi, %s." %(name))

Numero 3

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))

Numero 4

Fibonacci, tuple assignment

parents, babies = (1, 1)
while babies < 100:
    print("This generation has {0} babies".format(babies))
    parents, babies = (babies, parents+babies)

Numero 5

Functions

def greet(name):
    print("Hello", name)

greet("Jack")
greet("Jill")
greet("Bob")

Numero 6

Import, regular expressions

import re
for test_string in ['555-1212', 'ILL-EGAL']:
    if re.match(r'^\d{3}-\d{4}

Numero 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))

Numero 8

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")

Numero 9

Opening files

import glob                            # indent your Python code to put into an email
python_files = glob.glob('*.py')       # glob supports Unix style pathname extensions
for file_name in sorted(python_files):
    print('    ------' + file_name)
    with open(file_name) as f:
        for line in f:
            print ('    ' + line.rstrip())
    print()

Numero 10

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!')

Numero 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 = 9
while bottles_of_beer > 1:
    print(REFRAIN % (bottles_of_beer, bottles_of_beer, bottles_of_beer-1))
    bottles_of_beer -= 1

Numero 12

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())

Numero 13

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()

Numero 14

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()

Numero 15

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.

Numero 16

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)))

Numero 18

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)

Numero 20

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)

Numero 21

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))

Numero 28

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))

Numero 33

“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))

, test_string): print (test_string, 'is a valid US local phone number') else: print (test_string, 'rejected')