En esta charla veremos con detalle algunas de las construcciones más pythonicas y las posibilidades de expresar de forma clara, concisa y elegante cosas que en otros lenguajes nos obligarían a dar muchos rodeos. A veces es fácil olvidar algunos recursos como que una función puede devolver varios valores, cómo manipular listas y diccionarios de forma sencilla, contextos, generadores... En esta charla veremos de forma entretenida y práctica cómo mejorar nuestro nivel de Python "nativo".

1. Beautiful Python
@alipeji | alicia@stylesage.co

2. ¡Hola!
@alipeji | alicia@stylesage.co

3. El outfit perfecto
para un código pythonico

4. La ropa interior
tipos básicos
@stylishcurves

5. Strings

6. # Cadenas muy largas
my_very_big_string = 'For a long time I used to go to bed early. ' +
'Sometimes, when I had put out my candle, my eyes would close ' +
'so quickly that I had not even time to say Im going to sleep.'
my_very_big_string = '''For a long time I used to go to bed early.
Sometimes, when I had put out my candle, my eyes would close
so quickly that I had not even time to say Im going to sleep.'''
my_very_big_string = ('For a long time I used to go to bed early. '
'Sometimes, when I had put out my candle, my eyes would close '
'so quickly that I had not even time to say Im going to sleep.')

7. if stylesage.find('Fashion') != -1:
pass
# Comprobar si una cadena contiene otra
stylesage = 'Fashion meets Big Data'
if 'Fashion' in stylesage:
pass

8. >>> name = 'Alicia'
>>> cats = 2
>>> print('My name is ' + name + ' and I have ' + str(cats) + ' cats')
# Usa String Formatting!!

9. #1 – “Old Style”
>>> name = 'Bob'
>>> 'Hello, %s' % name
'Hello, Bob'
# String Formatting
#2 – “New Style” String Formatting
>>> name = 'Bob'
>>> 'Hello, {}'.format(name)
'Hello, Bob'
#3 – Literal String Interpolation
# (Python 3.6+)
>>> name = 'Bob'
>>> f'Hello, {name}'
'Hello, Bob'
#4 – Template Strings
>>> from string import Template
>>> t = Template('Hello, $name!')
>>> t.substitute(name='Bob')
'Hello, Bob!'

10. Booleanos

11. >>> if x >= start and x <= end:
>>> pass
>>> if len(items) != 0:
>>> pass
>>> if lang == 'Spanish':
... welcome = 'Bienvenido'
... else:
... welcome = 'Welcome'
>>> if start <= x <= end:
>>> pass
>>> if items:
>>> pass
>>> welcome = 'Bienvenido'
... if lang == 'Spanish' else 'Welcome'

12. Truth Value Testing
Los siguientes valores serán evaluados como False en una comparación:
● None
● False
● Cero en cualquier tipo numérico, por ejemplo: 0, 0L, 0.0, 0j
● Cualquier secuencia vacía, por ejemplo: '', (), []
● Los diccionarios vacíos: {}
● Las instancias de cualquier clase, si esta define los métodos __nonzero__() o __len__(),
cuando estos métodos devuelven cero o False
En cualquier otro caso, serán evaluados como True

13. >>> values = [True, True, False, False]
>>> i = 0
>>> flag = False
>>> while not flag and i < len(values):
... flag = values[i]
... i += 1
>>> flag
False
>>> any(values)
True
# ¿algún True en la lista?
>>> all(values)
False

14. >>> values = range(10) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> i = 0
>>> flag = False
>>> while not flag and i < len(values):
... flag = (values[i] == 0)
... i += 1
>>> flag
True
>>> any(values)
True
# ¿algún 0 en la lista?
>>> all(values)
False

15. Variables

16. >>> b, a = a, b>>> temp = a
>>> a = b
>>> b = temp
>>> l = ['David', 'Pythonista', '555-55-55']
>>> name = l[0]
>>> title = l[1]
>>> phone = l[2]
>>> name, title, phone = l
>>> name, _, phone = l

17. Los básicos
colecciones

18. Tuplas

19. # Crear una tupla
>>> arr = 'one', 'two', 'three'
>>> arr[0]
'One'
# Son immutables:
>>> arr[1] = 'hello'
TypeError:
"'tuple' object does not support
item assignment"
>>> del arr[1]
TypeError:
"'tuple' object doesn't support item
deletion"
# Soportan múltiples
# tipos de datos:
>>> arr + (23,)
('one', 'two', 'three', 23)

20. # namedtuples
>>> from collections
... import namedtuple
>>> Car = namedtuple('Car',
... 'color mileage automatic')
>>> car1 = Car('red', 3812.4, True)
# Acceder a los campos:
>>> car1.color
'red'
>>> car1.mileage
3812.4
>>> car1.automatic
True
# Los campos son inmutables:
>>> car1.mileage = 12
AttributeError: "can't set attribute"

21. Listas

22. # Crear una lista
>>> arr = ['one', 'two', 'three']
>>> arr[0]
'One'
# Son mutables:
>>> arr[1] = 'hello'
>>> arr
['one', 'hello', 'three']
>>> del arr[1]
>>> arr
['one', 'three']
# Soportan múltiples tipos:
>>> arr.append(23)
>>> arr
['one', 'three', 23]

23. # array slicing
a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[-1]
10
>>> a[2:8]
[2, 3, 4, 5, 6, 7]
>>> a[:5]
[0, 1, 2, 3, 4]
>>> a[5:]
[5, 6, 7, 8, 9, 10]
>>> a[2:8:2]
[2, 4, 6]
>>> a[::2]
[0, 2, 4, 6, 8, 10]
>>> a = [1, 2, 3, 4, 5]
>>> a[2:4] = [0, 0, 0]
>>> a
[1, 2, 0, 0, 0, 5]

24. Sets

25. >>> A = {1, 2, 3, 3}
>>> B = {3, 4, 5, 6, 7}
>>> A
set([1, 2, 3])
>>> B
set([3, 4, 5, 6, 7])
>>> A | B
set([1, 2, 3, 4, 5, 6, 7])
>>> A & B
set([3])
>>> A - B
set([1, 2])
>>> A ^ B
set([1, 2, 4, 5, 6, 7])

26. >>> A
Counter({2: 2, 1: 1})
>>> B
Counter({2: 2, 3: 1})
>>> C.most_common()
[(3, 4), (1, 2), (2, 2), (4, 1), (5, 1),
(6, 1), (7, 1)]
>>> C.most_common(1)
[(3, 4)]
>>> C.most_common(3)
[(3, 4), (1, 2), (2, 2)]
>>> A = collections.Counter([1, 2, 2])
>>> B = collections.Counter([2, 2, 3])
>>> C = collections.Counter([1, 1, 2, 2, 3, 3, 3, 3, 4, 5, 6, 7])
>>> A | B
Counter({2: 2, 1: 1, 3: 1})
>>> A & B
Counter({2: 2})
>>> A + B
Counter({2: 4, 1: 1, 3: 1})

27. Bucles “pythonicos”

28. >>> a = ['Hello', 'world', '!']
>>> for i, x in enumerate(a):
... print '{}: {}'.format(i, x)
>>> a = ['Hello', 'world', '!']
>>> i = 0
>>> for x in a:
... print '{}: {}'.format(i, x)
... i += 1
# Imprimir los elementos de una lista y su índice

29. >>> squares = [x * x for x in range(10)]>>> even_squares = []
>>> for x in range(10):
... even_squares.append(x * x)
>>> even_squares = []
>>> for x in range(10):
... if x % 2 == 0:
... even_squares.append(x * x)
>>> even_squares = [x * x for x in range(10)
... if x % 2 == 0]
# Obtener todos los cuadrados de los números del 0 al 9
# Obtener todos los cuadrados de los números pares del 0 al 9

30. >>> zip(names, surnames)
[('John', 'Cleese'), ('Eric', 'Idle'),
('Terry', 'Gilliam')]
>>> names = ['John', 'Eric', 'Terry']
>>> surnames = ['Cleese', 'Idle', 'Gilliam']
>>> people = []
>>> for i in range(len(names)):
... people.append((names[i], surnames[i]))
>>> print(people)
[('John', 'Cleese'), ('Eric', 'Idle'),
('Terry', 'Gilliam')]
# Obtener en una sola lista los pares nombre-apellido

31. Generadores

32. >>> squares = (i*i for i in xrange(1000000))
>>> next(squares)
0
>>> next(squares)
1
>>> next(squares)
4
>>> next(squares)
9
>>> next(squares)
16
>>> from collections import deque
>>> q = deque(squares)
>>> q.pop()
999998000001
>>> q.pop()
999996000004
>>> q.popleft()
0
>>> q.popleft()
1
>>> squares = [i*i for i in range(1000000)]

33. # Add to the right
>>> d = collections.deque()
>>> d.extend([0, 1, 2, 3, 4])
deque([0, 1, 2, 3, 4])
>>> d.append(5)
deque([0, 1, 2, 3, 4, 5])
# Add to the left
>>> d = collections.deque()
>>> d.extendleft([0, 1, 2, 3, 4])
deque([4, 3, 2, 1, 0])
>>> d.appendleft(5)
deque([5, 4, 3, 2, 1, 0])

34. >>> last_three = collections.deque(maxlen=3)
>>> for i in xrange(5):
... last_three.append(i)
... print ', '.join(
... str(x) for x in last_three)
0
0, 1
0, 1, 2
1, 2, 3
2, 3, 4

35. La “pieza luz”
diccionarios

36. Valores por defecto

37. >>> name_for_userid = {
... 382: 'Alice',
... 950: 'Bob',
... 590: 'Dilbert',
... }
>>> def greeting(userid):
... if userid in name_for_userid:
... return 'Hi %s!' % name_for_userid[userid]
... else:
... return 'Hi there!'

38. >>> def greeting(userid):
... try:
... return 'Hi %s!' % name_for_userid[userid]
... except KeyError:
... return 'Hi there'
>>> def greeting(userid):
... return 'Hi %s!' % user_dict.get(userid, 'there')

39. >>> visits = {
... 'Alice': 0,
... 'Bob': 0,
... 'Dilbert': 0,
... }
>>> def add_visit(user):
... if user not in visits:
... visits[user] = 0
... visits[user] += 1
>>> def add_visit(user):
... visits.setdefault(user, 0)
... visits[user] += 1
>>> def add_visit(user):
... visits[user] = visits.get(user, 0) + 1
>>> visits = defaultdict(int)
>>> def add_visit(user):
... visits[user] += 1

40. Comprensión

41. >>> m = {x: x ** 2 for x in range(5)}
>>> m
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
>>> m = {x: 'A' + str(x) for x in range(5)}
>>> m
{0: 'A0', 1: 'A1', 2: 'A2', 3: 'A3', 4: 'A4', 5}
>>> # Invertir las clave-valor
>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
>>> {v: k for k, v in m.items()}
{1: 'a', 2: 'b', 3: 'c', 4: 'd'}

42. Complementos

43. Parámetros (args & kwargs)

44. # * args
>>> def test_var_args(f_arg, *argv):
... print "first normal arg:", f_arg
... for arg in argv:
... print "another arg through *argv :", arg
>>> test_var_args()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: test_var_args() takes at least 1 argument (0 given)
>>> test_var_args('yasoob', 'python', 'eggs', 'test')
'first normal arg: yasoob'
'another arg through *argv : python'
'another arg through *argv : eggs'
'another arg through *argv : test'

45. # ** kargs
>>> def greet_me(**kwargs):
... for key, value in kwargs.iteritems():
... print "%s == %s" %(key,value)
>>> greet_me(name="yasoob")
'name == yasoob'
>>> kwargs = {"arg3": 3, "arg2": "two", "arg1":5}
>>> greet_me(**kwargs)
'arg1 == 5'
'arg2 == two'
'arg3 == 3'

46. Asserts

47. >>> def apply_discount(product, discount):
... price = int(product['price'] * (1.0 - discount))
... assert 0 <= price <= product['price']
... return price
>>> shoes = {'name': 'Fancy Shoes', 'price': 14900}
>>> apply_discount(shoes, 0.25)
11175
>>> apply_discount(shoes, 2.0)
Traceback (most recent call last):
File "<input>", line 1, in <module>
apply_discount(prod, 2.0)
File "<input>", line 4, in
apply_discount
assert 0 <= price <= product['price']
AssertionError

48. # internamente un assert es...
>>> if __debug__:
... if not expression1:
... raise AssertionError(expression2)
# por eso nunca hay que hacer...
>>> def delete_product(prod_id, user):
>>> assert user.is_admin(), 'Comprueba si es administrador'
>>> assert store.has_product(prod_id), 'Comprueba si existe'
>>> store.get_product(prod_id).delete()

49. Contextos

50. // WARNING!! Código Java en una charla Python!!
void muestraContenido(String archivo) throws FileNotFoundException, IOException {
String cadena;
FileReader f = new FileReader(archivo);
BufferedReader b = new BufferedReader(f);
while((cadena = b.readLine())!=null) {
System.out.println(cadena);
}
b.close();
}

51. with open(fname, 'r') as file_in:
print file_in.read()

52. class File():
def __init__(self, filename, mode):
self.filename = filename
self.mode = mode
def __enter__(self):
self.open_file = open(self.filename, self.mode)
return self.open_file
def __exit__(self, *args):
self.open_file.close()

53. Referencias Python Tricks: The Book
A Buffet of Awesome Python Features
30 Python Language Features and Tricks
You May Not Know About
PYTHON TIPS web

54. ¡Gracias!
@alipeji | alicia@stylesage.co