Python Idiomático

Transcript

1. @dialelo | github.com/alejandrogomez Python Idiomático
2. Idiomático Perteneciente o conforme al modo de expresión de un lenguaje (de programación).
3. import this
4. from __future__ import print_function
5. Unpacking
6. ☹ favorite_color = [0xBA, 0xDA, 0x55] red = favorite_color[0] green = favorite_color[1] blue = favorite_color[2]
7. ☺ favorite_color = [0xBA, 0xDA, 0x55] red, green, blue = favorite_color
8. 3 head, *body, tail = range(5) # head == 0 # body == [1, 2, 3] # tail == 4
9. Slices
10. ☹ person_info = ('Alejandro', 19, 12, 1988, '#BADA55') person = Person(person_info[0], person_info[1:4], person_info[4])
11. ☺ person_info = ('Alejandro', 19, 12, 1988, '#BADA55') NAME = slice(0, 1) BIRTH_DATE = slice(1, 4) FAVORITE_COLOR = slice(4, 5) person = Person(person_info[NAME], person_info[BIRTH_DATE], person_info[FAVORITE_COLOR])
12. Strings
13. ☹ family_members = 'Mikel' family_members += ', Ángel' family_members += ', Isabel'
14. ☺ names = ('Mikel', 'Ángel', 'Isabel') family_members = ', '.join(names)
15. Iteración Con índice
16. colors = ['red', 'green', 'blue']
17. ☹ for i in range(len(colors)): print( colors[{}] : {} .format(i, colors[i])) “ ”
18. ☺ for i, color in enumerate(colors): print( colors[{}] : {} .format(i, colors)) “ ”
19. Iteración A la inversa
20. ☹ for color in colors[::-1]: print(color)
21. ☺ for color in reversed(colors): print(color)
22. Iteración En orden
23. ☺ for color in sorted(colors): print(color)
24. • ¿Necesitas definir el orden? – Prefiere key a cmp – key sólo se llama una vez por elemento – cmp compara pares de elementos, no está en Python 3
25. ☺ for color in sorted(colors, key=len): print(color)
26. from functools import cmp_to_key @cmp_to_key def my_comparison(a, b): # ...
27. Iteración iter
28. • iter tiene dos formas – iter(collection) → iterador – iter(callable, sentinel) → iterador
29. ☹ while True: value = read_value() if value is None: break else: do_something(value)
30. ☺ for value in iter(read_value, None): do_something(value)
31. Diccionarios Iterar
32. d = { 'red': 0xBA, 'green': 0xDA, 'blue': 0x55 } # `for` itera sobre las claves for k in d: print(k)
33. ☹☹ for k in d: print( {} : {} .format(k, d[k])) “ ”
34. ☹ for k, v in d.items(): print( {} : {} .format(k, v)) “ ”
35. ☺ for k, v in d.iteritems(): print( {} : {} .format(k, v)) “ ”
36. 3 for k, v in d.items(): print( {} : {} .format(k, v)) “ ”
37. Diccionarios Construir
38. colors = ['red', 'green', 'blue'] values = [0xBA, 0xDA, 0x55]
39. ☹ d = dict(zip(colors, values))
40. ☺ from itertools import izip d = dict(izip(colors, values))
41. ☺ from itertools import izip d = {c: v for (c, v) in izip(colors, values)}
42. Diccionarios Combinar
43. one = { 'foo': 42 } another = { 'bar': None, 'baz': 8 } yet_another = { 'foo': 1, 'baz': 0 }
44. ☹ merged = {} for d in (one, another, yet_another): merged.update(d)
45. 3 from collections import ChainMap d = ChainMap(one, another, yet_another)
46. Django from django.utils.datastructures import MergeDict # funciona al revés que `collections.ChainMap` ☹ d = MergeDict(yet_another, another, one)
47. ☺ from itertools import izip d = {c: v for (c, v) in izip(colors, values)}
48. Funciones λ
49. people = [{ 'name': 'Zoe' }, { 'name': 'Bob' }, { 'name': 'Alice' }]
50. ☹ for p in sorted(people, key=lambda p: p['name']): print(p)
51. ☺ from operators import itemgetter for p in sorted(people, key=itemgetter('name')): print(p)
52. Funciones Argumentos
53. results = search('#codemotion', 10) # ¿qué es 10? results = search('#codemotion', min_retweets=10) results = search('#codemotion', limit=10)
54. • Argumentos con nombre – ☺ Código más legible – ☺ Parámetros documentados – ☹ Coste en rendimiento
55. Funciones Valores de retorno
56. def run_tests(): # … return (passed, failed, skipped)
57. ☹ passed, failed, skipped = run_tests()
58. from collections import namedtuple TestResults = namedtuple('TestResults', [ 'passed', 'failed', 'skipped']) def run_tests(): # … return TestResults(passed, failed, skipped)
59. ☺ results = run_tests() # results.passed # results.failed # results.skipped
60. Context Managers
61. • Setup y teardown – Operaciones de entrada/salida – Locks – Contexto
62. ☹ f = open('readme.md') try: content = f.read() finally: f.close()
63. ☺ with open('readme.md') as f: content = f.read()
64. Excepciones
65. ☹☹ import os try: os.remove('readme.md') except: pass
66. ☹ import os try: os.remove('readme.md') except OSError: pass
67. ☹ 3 import os try: os.remove('readme.md') except FileNotFoundError: pass
68. ☺ >= 3.4 from contextlib import ignored with ignored(FileNotFoundError): os.remove('readme.md')
69. ☺ < 3.4 from contextlib import contextmanager @contextmanager def ignored(*exceptions): try: yield except exceptions: pass
70. Generator expressions
71. • Equivalentes a las comprensiones de listas pero perezosas – Manipulación de secuencias en múltiples pasos – Secuencias como resultados intermedios
72. ☹ uppercase_lines = [l.upper() for l in open('readme.md')] filtered_lines = [l for l in uppercase_lines if l.startswith('#')] # ¿qué pasa si readme.md es un fichero ENORME? for l in filtered_lines: print(l)
73. ☺ uppercase_lines = (l.upper() for l in open('readme.md')) filtered_lines = (l for l in uppercase_lines if l.startswith('#')) # la iteración dirige la evaluación de las genexpressions for l in filtered_lines: print(l)
75. Escribid código bonito
76. ¡Gracias!