Pytfalls

Transcript

1. PYTFALLS

2. WHOAMI ▸ desenvolvedor na Jusbrasil ▸ contribui com projetos open

   source como Django, Docker, OpenStack, pypy, splinter, tsuru ▸ github.com/andrewsmedina

3. PYTFALLS??!!

4. A HIDDEN OR UNSUSPECTED DANGER OR DIFFICULTY PITFALL

5. AN UNEXPECTED PROBLEM OR USUALLY UNPLEASANT SURPRISE GOTCHA

6. None
7. None
8. None

9. Há muito tempo, numa linguagem muito distante…

10. > 1 + 1

11. > 1 + 1 2

12. > 1 + “1”

13. > 1 + “1” “11”

14. > 1 + “1” “11”

15. > “11” - 1

16. > “11” - 1

17. > “11” - 1 10

18. > “11” - 1 10

19. > “JS” - 1

20. > “JS” - 1 NaN

21. > “JS” - 1 NaN

22. > Array(16).join("JS" - 2) + " Batman!"

23. > Array(16).join("JS" - 2) + " Batman!" "NaNNaNNaNNaNNaNNaNNaNNaNNa NNaNNaNNaNNaNNaNNaN Batman!"

24. None

25. PYTHON

26. É UMA LINGUAGEM INTUITIVA PYTHON

27. ZEN OF PYTHON PYTHON

28. É LEGÍVEL PYTHON

29. CRIADA EM 1991 PYTHON

30. “There should be one-- and preferably only one --obvious way

    to do it.”

31. urllib httplib urllib3

32. urllib httplib urllib3

33. “Explicit is better than implicit.”

34. >>> "Oi" + u" mundo" u'Oi mundo'

35. >>> "Oi" + u" mundo" u'Oi mundo'

36. #1

37. Python 2

38. USE PYTHON3 TL;DR

39. #2

40. def append(element, to=[]): to.append(element) return to

41. >>> my_list = append(12) >>> print(my_list) ??? >>> my_other_list =

    append(42) print(my_other_list) ???

42. >>> my_list = append(12) >>> print(my_list) [12] >>> my_other_list =

    append(42) print(my_other_list) ???

43. >>> my_list = append(12) >>> print(my_list) [12] >>> my_other_list =

    append(42) print(my_other_list) [12, 42]

44. >>> my_list = append(12) >>> print(my_list) [12] >>> my_other_list =

    append(42) print(my_other_list) [12, 42]

45. def append(element, to=[]): to.append(element) return to

46. def append(element, to=None): if to is None: to = []

    to.append(element) return to

47. def fib(n): if n <= 2: data = 1 else:

    data = fib(n - 2) + fib(n - 1) return data

48. def fib(n, cache={}): if n not in cache: if n

    <= 2: data = 1 else: data = fib(n - 2) + fib(n - 1) cache[n] = data return cache[n]

49. #3

50. def create_multipliers(): return [lambda x : i * x for

    i in range(5)]

51. for multiplier in create_multipliers(): print multiplier(2)

52. for multiplier in create_multipliers(): print multiplier(2) ? ? ? ?

53. for multiplier in create_multipliers(): print multiplier(2) ? (0) ? (2)

    ? (4) ? (6)

54. for multiplier in create_multipliers(): print multiplier(2) 8 8 8 8

55. for multiplier in create_multipliers(): print multiplier(2) 8 8 8 8

56. def create_multipliers(): return [lambda x : i * x for

    i in range(5)]

57. def create_multipliers(): multipliers = [] for i in range(5): def

    multiplier(x): return i * x multipliers.append(multiplier) return multipliers

58. def soma(x, y): return x+y

59. soma = lambda x, y: x+y

60. def soma(x, y): return x+y

61. def create_multipliers(): return [lambda x : i * x for

    i in range(5)]

62. def create_multipliers(): multipliers = [] for i in range(5): def

    multiplier(x): return i * x multipliers.append(multiplier) return multipliers

63. def create_multipliers(): return [lambda x, i=i: i * x for

    i in range(5)]

64. #4

65. >>> a = 256 >>> b = 256 >>> a

    is b True

66. >>> a = 257 >>> b = 257 >>> a

    is b ???

67. >>> a = 257 >>> b = 257 >>> a

    is b False

68. >>> a = 257 >>> b = 257 >>> a

    is b False

69. >>> a = 256 >>> b = 256 >>> a

    is b True

70. >>> help(id)

71. >>> help(id) id(obj, /) Return the identity of an object.

72. >>> a = 256 >>> id(a) 4307458704 >>> b =

    256 >>> id(b) 4307458704

73. >>> a = 257 >>> id(257) 4312868592 >>> b =

    257 >>> id(b) 4311130416

74. #5

75. # random.py import random random.randrange(100)

76. $ python random.py Traceback (most recent call last): File "random.py",

    line 1, in <module> import random File "random.py", line 3, in <module> print(random.randrange(100)) AttributeError: 'module' object has no attribute 'randrange'

77. #6

78. *.pyc

79. $ find . -name "*.pyc" -delete

80. export PYTHONDONTWRITEBYTECODE=1

81. >>> import sys >>> sys.dont_write_bytecode True

82. $ python -B main.py

83. #7

84. >>> linguagens = {} >>> linguagens[1] = “Python” >>> linguagens[1.0]

    = “Go” >>> linguagens[1] “Go”

85. >>> hash(1) == hash(1.0) True

86. #8

87. >>> x = [[]] * 5 >>> x [[], [],

    [], [], []] >>> x[0].append(1) ????

88. >>> x[0].append(1) ????

89. >>> x[0].append(1) # [[0], [], [], [], []] ok?

90. >>> x[0].append(1) [[1], [1], [1], [1], [1]]

91. >>> x[0].append(1) [[1], [1], [1], [1], [1]]

92. >>> id(x[0]) 4390176008 >>> id(x[1]) 4390176008

93. #9

94. class Hero: life = 100 class Dragon(Hero): pass class Giant(Hero):

    pass

95. >>> Hero.life, Giant.life, Dragon.life 100, 100, 100

96. >>> Hero.life = 10 >>> Hero.life, Giant.life, Dragon.life

97. >>> Hero.life = 10 >>> Hero.life, Giant.life, Dragon.life ?, ?,

    ?

98. >>> Hero.life = 10 >>> Hero.life, Giant.life, Dragon.life 10, 10,

    10

99. >>> Giant.life = 300 >>> Hero.life, Giant.life, Dragon.life ?, ?,

    ?

100. >>> Giant.life = 300 >>> Hero.life, Giant.life, Dragon.life 10, 300,

     10

101. >>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life ?, ?,

     ?

102. >>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life 50, 300,

     50

103. >>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life 50, 300,

     50

104. Hero (life=50) Giant (life=300) Dragon

105. #10

106. class Hero: spells = []

107. >>> dragon = Hero() >>> dragon.spells.append(“fireball”) >>> dragon.spells [“fireball”]

108. >>> priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells ???

109. >>> priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells [“fireball”, “heal”]

110. >>> priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells [“fireball”, “heal”]

111. class Hero: spells = []

112. class Hero: def __init__(self): self.spells = []

113. >>> dragon = Hero() >>> dragon.spells.append(“fireball”) >>> dragon.spells [“fireball”] >>>

     priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells [“heal”]

114. #DICAS

115. None
116. None
117. None

118. OBRIGADO!