Pytfalls

Transcript

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   PYTFALLS

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   WHOAMI ▸ desenvolvedor na Jusbrasil ▸ contribui com projetos open

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

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   A HIDDEN OR UNSUSPECTED DANGER OR DIFFICULTY PITFALL

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   AN UNEXPECTED PROBLEM OR USUALLY UNPLEASANT SURPRISE GOTCHA

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   None
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   None
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   None
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   Há muito tempo, numa linguagem muito distante…

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    > 1 + 1

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    > 1 + 1 2

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    > 1 + “1”

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    > 1 + “1” “11”

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    > 1 + “1” “11”

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    > “11” - 1

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    > “11” - 1

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    > “11” - 1 10

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    > “11” - 1 10

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    > “JS” - 1

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    > “JS” - 1 NaN

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    > “JS” - 1 NaN

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

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

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    None
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    PYTHON

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    É UMA LINGUAGEM INTUITIVA PYTHON

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    ZEN OF PYTHON PYTHON

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    É LEGÍVEL PYTHON

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    CRIADA EM 1991 PYTHON

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

    to do it.”
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    urllib httplib urllib3

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    urllib httplib urllib3

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    “Explicit is better than implicit.”

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    >>> "Oi" + u" mundo" u'Oi mundo'

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    >>> "Oi" + u" mundo" u'Oi mundo'

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    #1

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    Python 2

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    USE PYTHON3 TL;DR

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    #2

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

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

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

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

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

    append(42) print(my_other_list) [12, 42]
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    def append(element, to=[]): to.append(element) return to

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

    to.append(element) return to
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    def fib(n): if n <= 2: data = 1 else:

    data = fib(n - 2) + fib(n - 1) return data
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    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]
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    #3

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

    i in range(5)]
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    for multiplier in create_multipliers(): print multiplier(2)

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

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

    ? (4) ? (6)
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    for multiplier in create_multipliers(): print multiplier(2) 8 8 8 8

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

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

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

    multiplier(x): return i * x multipliers.append(multiplier) return multipliers
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    def soma(x, y): return x+y

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    soma = lambda x, y: x+y

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

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

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

    multiplier(x): return i * x multipliers.append(multiplier) return multipliers
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    def create_multipliers(): return [lambda x, i=i: i * x for

    i in range(5)]
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    #4

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    >>> a = 256 >>> b = 256 >>> a

    is b True
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    >>> a = 257 >>> b = 257 >>> a

    is b ???
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    >>> a = 257 >>> b = 257 >>> a

    is b False
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    >>> a = 257 >>> b = 257 >>> a

    is b False
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    >>> a = 256 >>> b = 256 >>> a

    is b True
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    >>> help(id)

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

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

    256 >>> id(b) 4307458704
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    >>> a = 257 >>> id(257) 4312868592 >>> b =

    257 >>> id(b) 4311130416
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    #5

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

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    $ 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'
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    #6

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    *.pyc

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

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    export PYTHONDONTWRITEBYTECODE=1

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

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    $ python -B main.py

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    #7

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

    = “Go” >>> linguagens[1] “Go”
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    >>> hash(1) == hash(1.0) True

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    #8

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

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

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

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

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

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

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    #9

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

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

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

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

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

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

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

     10
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     >>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life ?, ?,

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

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

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

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     #10

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     class Hero: spells = []

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

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

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

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

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     class Hero: spells = []

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

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

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

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     None
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     None
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     None
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     OBRIGADO!