python basics

quick introduction to the python language

https://github.com/rafael84/pyintro

Rafael L Martins <rafael84@gmail.com>

data types

int, long, float

str, unicode

lists

tuples

dictionaries

INT, LONG, FLOAT

# integer division

>>> x = 144

>>> y = 7

>>> x / y

# float division

>>> w = 124.5

>>> t = 3

>>> w / t

41.5

# float division (truncate)

>>> w = 124.5

>>> t = 3

>>> w // t

41.0

# type casting

>>> w = 124.5

>>> t = 3

>>> int(w / t)

INT, LONG, FLOAT

# long division

>>> k = 23L

>>> j = 7

>>> k / j

# long modulus

>>> b = 15L

>>> m = 5L

>>> b % m

# long exponentiation

>>> p = 2L

>>> q = 3L

>>> p ** q

str, unicode

# str

>>> s = 'João'

>>> type(s)

str

>>> print(s)

João

>>> repr(s)

"'Jo\\xc3\\xa3o'"

# unicode

>>> s = u'João'

>>> type(s)

unicode

>>> print(s)

João

>>> repr(s)

"u'Jo\\xe3o'"

>>> s = unicode('João')

>>> type(s)

unicode

# raw

>>> s = '\nA\n'

>>> print(s)

>>> s = r'\nA\n'

>>> print(s)

\nA\n

lists

>>> e = []

>>> type(e)

list

>>> f = [2,3] + [4+5]

>>> print(f)

[2, 3, 9]

>>> f[0] = 1

>>> print(f)

[1, 3, 9]

>>> h = [0, 1] * 3

[0, 1, 0, 1, 0, 1]

>>> h.count(0)

>>> h.sort()

>>> print(h)

[0, 0, 0, 1, 1, 1]

>>> h = range(5)

>>> print(h)

[0, 1, 2, 3, 4]

>>> h = range(3)

>>> h.reverse()

>>> print(h)

[2, 1, 0]

>>> h.index(0)

tUples

>>> r = ('a', 1, 3.14, None)

print r[0]

'a'

>>> type(r[1])

int

>>> r[2] = 'x'

TypeError: 'tuple' object does not support item assignment

tuples

>>> d = tuple([1, 2, 3])

>>> print(d)

(1, 2, 3)

>>> d.index(9)

ValueError: tuple.index(x): x not in tuple

>>> char, number, pi, null = r

>>> print(pi, null)

(3.14, None)

dictionaries

>>> v = {}

>>> v['w'] = 'R'

>>> v[0] = 100

>>> v[None] = 1.99

>>> print(v)

{0: 100, None: 1.99, 'w': 'R'}

>>> o = dict(a=123, b='456', c=99L)

>>> print(o)

{'a': 123, 'b': '456', 'c': 99L}

dictionaries

>>> o = {'a': 123, 'b': '456', 'c': 99L}

>>> o.items()

[('a', 123), ('c', 99L), ('b', '456')]

>>> o.keys()

['a', 'c', 'b']

>>> o.values()

[123, 99L, '456']

>>> print(o.get(555, 'not found'))

not found

dictionaries

>>> o = dict(a=1, b=2, c=3)

>>> o.has_key(a)

NameError: name 'a' is not defined

>>> o.has_key('a')

True

>>> da = dict(a=1)

>>> db = dict(b=2)

>>> dc = dict(da.items() + db.items())

>>> print(dc)

{'a': 1, 'b': 2}

BASIC commands

if ... elif ... else

while, break, continue

for ... in ... else

pass

TRY ... EXCEPT ... ELSE ... FINALLY

DEF

IF ... ELIF ... ELSE

# basic_commands/001_if_elif_else.py

import datetime                                                                

today = datetime.date.today()

day = today.day

if day in range(1, 10):
    print('give me my payment!')

elif day == 11:
    print('out of money')

else:
    print('oh my God!')

WHILE, break, continue

# basic_commands/002_while_break_continue.py

import random

places_to_eat = [
    'eskilos', 'cristovao', 'japanese', 'sativa', 'portuguese',
]

option = None

counter = 0
while option != 'eskilos':
    option = random.choice(places_to_eat)
    if option == 'eskilos':
        break
    counter += 1
    if option == 'portuguese':
        print 'Are you crazy? "Portuguese" is not a valid option!'
        continue
    print('Thinking of %s...' % option)

print('After {0} tries, you chose {1}.'.format(counter, option))
print('Good choice!')

FOR ... IN ... ELSE

# basic_commands/003_for_in_else.py

import random

numbers = []
for x in range(10):
    numbers.append(random.randint(-3, 20))

for number in numbers:
    print 'Checking number: %d' % number
    if number < 0:
        break
else:
    print 'You are lucky. All numbers are positive.'

PASS

# basic_commands/004_pass.py

def work_less_more_money():
    return 'OF COURSE!'


def borrow_some_money():
    pass


print 'Q: Less work, more money?'
print 'A: %s' % work_less_more_money()

print

print 'Q: I have no money, could you borrow me some?'
print 'A: %s' % borrow_some_money()

TRY ... EXCEPT ... ELSE ... FINALLY

# basic_commands/005_try_except_else_finally.py

import sys


def cat(filename):
    f = None
    try:
        f = open(filename)
    except IOError:
        print "could not open the file"
    else:
        for line in f:
            print line,
    finally:
        if f:
            f.close()


if len(sys.argv) == 2:
    cat(sys.argv[1])

DEF

# basic_commands/006_def.py

def sum(x, y):
    '''Returns the sum of two numbers'''
    return x + y


print help(sum)
print sum.__doc__

print sum(1, 2)


def welcome(name, greeting='hello'):
    print '%s %s, welcome!' % (greeting, name)


welcome('Peter')
welcome('Maria', 'hi there')

CLASSES

CLASS AND INHERITANCE

METHOD, SELF, SUPER

SPECIAL METHODS and attributes

PROPERTIES

CLASS AND INHERITANCE

# classes/007_class.py

class Stack:
    def __init__(self):
        self.items = []

    def push(self, item):
        self.items.append(item)

    def pop(self):
        x = self.items[-1]
        del self.items[-1]
        return x

    def empty(self):
        return len(self.items) == 0

stack = Stack()
for element in range(1, 10):
    stack.push(element)

while not stack.empty():
    print stack.pop()

class and inheritance

# classes/008_inheritance.py

class Hero:
    def __init__(self, name):
        self.name = name

class Cyclops(Hero):
    def optic_blast(self):
        print '%s is using optic blast...' % self.name

class Flash(Hero):
    def move_super_fast(self):
        print '%s is moving super fast...' % self.name

class SuperMan(Cyclops, Flash):
    def fly(self):
        print '%s is flying like a bird...' % self.name

hero = SuperMan('Clark Kent')
hero.optic_blast()
hero.move_super_fast()
hero.fly()

METHOD, SELF, SUPER

# classes/009_method_self_super.py

class Todo(object):
    def __init__(self, description, completed):
        self.description = description
        self.completed = completed
    def __str__(self):
        done = 'X' if self.completed else ' '
        return '[%s] %s' % (done, self.description)

class FancyTodo(Todo):
    def __str__(self):
        s = super(FancyTodo, self).__str__()
        return '%s\n%s\n%s' % ('=' * len(s), s, '-' * len(s))

todoList = []
todoList.append(Todo('Buy some coffee', True))
todoList.append(Todo('Make a lot of coffee', False))
todoList.append(Todo('Drink much more coffee', False))
todoList.append(FancyTodo('Lose weight', True))
todoList.append(FancyTodo('Eat less bacon', False))

for todo in todoList: print todo

SPECIAL METHODS and attributes

# classes/010_special_methods.py

def explore(obj):
    cls = obj.__class__
    name = cls.__name__
    members = cls.__dict__.items()

    print 'class %s(object):' % name
    for name, value in members:
        if not name.startswith('__'):
            if hasattr(value, '__call__'):
                print '\tdef %s(): pass' % name
            else:
                print '\t%s = %s' % (name, value)

class Foo(object):
    bar = 123
    xpto = 'abc'

    def baz(self):
        pass

explore(Foo())

PROPERTIES

# classes/011_properties.py

class Person(object):
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

    @property
    def name(self):
        return '%s %s' % (self.first_name, self.last_name)

    @name.setter
    def name(self, value):
        s = value.split()
        self.first_name = s[0]
        self.last_name = ' '.join(s[1:])


john = Person('John', 'Smith')
print john.name

john.name = 'John Brown Smith'
print john.name

MODULES

PACKAGEs and modules

IMPORT AND FROM ... IMPORT

python path

PACKAGEs and modules

Sample structure

├── pkg1
│   ├── __init__.py       # special module that makes pkg1 a package
│   └── subpkg1
│       └── __init__.py   # special module that makes subpkg1 a package
└── pkg2
    ├── __init__.py       # special module that makes pkg2 a package
    ├── subpkg1
    │   ├── __init__.py   # special module that makes subpkg1 a package
    │   ├── module1.py    # a normal module
    │   └── module2.py    # another normal module
    └── subpkg2
        └── __init__.py   # makes subpkg2 a package

Each module contains

print "module: %s" % __name__

import and FROM ... IMPORT

SAMPLE IMPORTS USING THE PREVIOUS STRUCTURE

$ python -c 'import pkg1'
module: pkg1


$ python -c 'import pkg1.subpkg1'
module: pkg1
module: pkg1.subpkg1


$ python -c 'import pkg2.subpkg1.module2'
module: pkg2
module: pkg2.subpkg1
module: pkg2.subpkg1.module2


$ python -c 'from pkg2.subpkg1 import module2'
module: pkg2
module: pkg2.subpkg1
module: pkg2.subpkg2.module2

PYTHON PATH

CHECKING THE PYTHONPATH

$ python -c 'import sys; from pprint import pprint; pprint(sys.path)'

['',
 '/home/you/.virtualenvs/pyintro/local/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
 '/home/you/.virtualenvs/pyintro/local/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg',
 '/home/you/.virtualenvs/pyintro/lib/python2.7',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/plat-linux2',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/lib-tk',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/lib-old',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/lib-dynload',
 '/usr/lib/python2.7',
 '/usr/lib/python2.7/plat-linux2',
 '/usr/lib/python2.7/lib-tk',
 '/home/you/.virtualenvs/pyintro/local/lib/python2.7/site-packages',
 '/home/you/.virtualenvs/pyintro/lib/python2.7/site-packages']

PYTHONPATH

Sample project struture

├── admin
│   ├── __init__.py
│   ├── models.py
│   └── views.py
└── main.py

main.py

#!/usr/bin/env python
#-*- coding: utf-8 -*-

import sys
import os

from admin.models import MyModel
from admin.views import MyView

extra topics

slice notation

list comprehension

PACKING AND UNPACKING

with statement

iterators and generators

UNIT TESTING

SLICE notation

# extra_topics/012_slice_notation.py

#  +---+---+---+---+---+---+---+---+---+---+---+
#  | H | e | l | l | o |   | W | o | r | l | d |
#  +---+---+---+---+---+---+---+---+---+---+---+
#    0   1   2   3   4   5   6   7   8   9  10   # offset from start
#  -11 -10  -9  -8  -7  -6  -5  -4  -3  -2  -1   # offset from end

s = 'Hello World'

print s[0]          # H
print s[-11]        # H
print s[1]          # e

print s[-1]         # d
print s[-2]         # l

print s[0:5]        # Hello
print s[6:]         # World
print s[:-6]        # Hello

print s[::-1]       # dlroW olleH

LIST COMPREHENSION

# extra_topics/013_list_comprehension.py

squares = []
for x in range(10):
    squares.append(x ** 2)
print squares

# OR

squares = [x ** 2 for x in range(10)]
print squares

# extra_topics/014_list_comprehension_if.py

numbers = [-3, 8, 56, -77, 100, -1, 5]
print 'All: %s' % numbers

positive = [number for number in numbers if number > 0]
print 'Positive: %s' % positive

negative = [number for number in numbers if number < 0]
print 'Negative: %s' % negative

PACKING AND UNPACKING

# extra_topics/015_packing_and_unpacking_args.py

def extract_positive(*numbers):
    return [number for number in numbers if number > 0]

def sum_all(*numbers):
    total = 0
    for number in numbers: total += number
    return total

def sum_all_positive(*numbers):
    positive = extract_positive(*numbers)
    return sum_all(*positive)

print extract_positive(-1, -2, -3, 10, 20, 30)
print sum_all(-1, -2, -3, 10, 20, 30)
print sum_all_positive(-1, -2, -3, 10, 20, 30)

# extra_topics/016_packing_and_unpacking_kwargs.py

def print_params(*args, **kwargs):
    print '%s: %s' % (type(args), args)
    print '%s: %s' % (type(kwargs), kwargs)

print_params(1, 2, 3, foo='a', bar='2')

WITH STATEMENT

# extra_topics/017_with_statement.py

import time


class Timer:
    def __enter__(self):
        self.time = time.time()
        print 'Processing...'

    def __exit__(self, type, value, traceback):
        ellapsed = time.time() - self.time
        print 'Done in %s' % ellapsed

with Timer():
    for x in range(100000000L):
        pass

iterators and GENERATORs

# extra_topics/018_iterator.py

a = iter(range(10))
print 'iterator has next: %s' % hasattr(a, 'next')

print a.next()  # 0
print a.next()  # 1
print a.next()  # 2

for n in a:
    print n  # calls a.next(), from 3 to 9

b = [100, 200, 300, 400, 500]
print 'list has an iterator: %s' % hasattr(b, '__iter__')

b_iter = b.__iter__()
print 'type of list iterator: %s' % type(b_iter)

print 'list iterator has next: %s' % hasattr(b_iter, 'next')

print b_iter.next()  # 100
print b_iter.next()  # 200
print b_iter.next()  # 300
print b_iter.next()  # 400

iterators and generators

# extra_topics/019_generator_expression.py

g = (x ** x for x in range(5))

print 'type of g: %s' % type(g)

print 'g has next: %s' % hasattr(g, 'next')

print g.next()  # 0**0 = 1
print g.next()  # 1**1 = 1
print g.next()  # 2**2 = 4
print g.next()  # 3**3 = 9

print 'generator has an iterator: %s' % hasattr(g, '__iter__')

g_iter = g.__iter__()
print 'type of generator iterator: %s' % type(g_iter)

print 'generator iterator has next: %s' % hasattr(g_iter, 'next')

print g_iter.next()  # 4**4 = 256

iterators and generators

# extra_topics/020_yield.py

import random


def random_generator(n):
    c = 0
    print 'before while'
    while c < n:
        print '\tbefore yield'
        yield random.randint(1, 1000)
        print '\tafter yield'
        c += 1
    print 'after while'

print 'type of random_generator: %s' % type(random_generator)

rg3 = random_generator(3)
print 'type of random_generator(3): %s' % type(rg3)

for r in rg3:
    print '\t\tinside for-loop: %s' % r

UNIT TESTING

# extra_topics/unit_testing/calc.py
    
class Calculator(object):
    def sum(self, x, y):
        return x + y

# extra_topics/unit_testing/test_calc.py

import unittest
import calc


class TestCalc(unittest.TestCase):

    def setUp(self):
        self.calc = calc.Calculator()

    def test_sum(self):
        expected = 7
        got = self.calc.sum(2, 5)
        self.assertEqual(expected, got, '2 + 5 should be equal to 7')

unit testing

$ python -m unittest test_calc

.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

$ python -m unittest -v test_calc
    
test_sum (test_calc.TestCalc) ... ok

----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

$ python -m unittest -v test_calc.TestCalc.test_sum

test_sum (test_calc.TestCalc) ... ok

----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

THANK YOU!

python basics

By Rafael L Martins

python basics

1,031

Rafael L Martins

def me(): return " dev* "

python basics

quick introduction to the python language

data types

int, long, float str, unicode lists tuples dictionaries

INT, LONG, FLOAT

INT, LONG, FLOAT

str, unicode

lists

tUples

tuples

dictionaries

dictionaries

dictionaries

BASIC commands

if ... elif ... else while, break, continue for ... in ... else pass TRY ... EXCEPT ... ELSE ... FINALLY DEF

IF ... ELIF ... ELSE

WHILE, break, continue

FOR ... IN ... ELSE

PASS

TRY ... EXCEPT ... ELSE ... FINALLY

DEF

CLASSES

CLASS AND INHERITANCE METHOD, SELF, SUPER SPECIAL METHODS and attributes PROPERTIES

CLASS AND INHERITANCE

class and inheritance

METHOD, SELF, SUPER

SPECIAL METHODS and attributes

PROPERTIES

MODULES

PACKAGEs and modules IMPORT AND FROM ... IMPORT python path

PACKAGEs and modules

Sample structure

Each module contains

import and FROM ... IMPORT

SAMPLE IMPORTS USING THE PREVIOUS STRUCTURE

PYTHON PATH

CHECKING THE PYTHONPATH

PYTHONPATH

Sample project struture

main.py

extra topics

slice notation list comprehension PACKING AND UNPACKING with statement iterators and generators UNIT TESTING

SLICE notation

LIST COMPREHENSION

PACKING AND UNPACKING

WITH STATEMENT

iterators and GENERATORs

iterators and generators

iterators and generators

UNIT TESTING

unit testing

THANK YOU!

python basics

More from Rafael L Martins

int, long, float

str, unicode

lists

tuples

dictionaries

if ... elif ... else

while, break, continue

for ... in ... else

pass

TRY ... EXCEPT ... ELSE ... FINALLY

DEF

CLASS AND INHERITANCE

METHOD, SELF, SUPER

SPECIAL METHODS and attributes

PROPERTIES

PACKAGEs and modules

IMPORT AND FROM ... IMPORT

python path

slice notation

list comprehension

PACKING AND UNPACKING

with statement

iterators and generators

UNIT TESTING