Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Pytfalls
Search
Andrews Medina
June 11, 2017
Technology
1
190
Pytfalls
Conhecendo e explorando comportamentos não intuitivos do Python
Andrews Medina
June 11, 2017
Tweet
Share
More Decks by Andrews Medina
See All by Andrews Medina
Organizando dados juŕidicos em grafos
andrewsmedina
0
99
Clean Code - princípios e práticas para um código sustentável
andrewsmedina
0
630
tsuru para quem sabe tsuru
andrewsmedina
0
77
globo.com s2 python
andrewsmedina
5
390
tsuru and docker
andrewsmedina
6
3.5k
pypy - o interpretador mais rapido do velho oeste
andrewsmedina
0
390
fazendo deploys de forma simples e divertida com tsuru
andrewsmedina
3
140
let's go
andrewsmedina
2
310
TDD for Dummies
andrewsmedina
3
370
Other Decks in Technology
See All in Technology
Backboneとしてのtimm2025
yu4u
3
1.1k
[CV勉強会@関東 CVPR2025 読み会] MegaSaM: Accurate, Fast, and Robust Structure and Motion from Casual Dynamic Videos (Li+, CVPR2025)
abemii
0
170
Android Studio の 新しいAI機能を試してみよう / Try out the new AI features in Android Studio
yanzm
0
160
LLM時代の検索とコンテキストエンジニアリング
shibuiwilliam
2
1k
いま、あらためて考えてみるアカウント管理 with IaC / Account management with IaC
kohbis
2
560
九州の人に知ってもらいたいGISスポット / gis spot in kyushu 2025
sakaik
0
220
歴代のWeb Speed Hackathonの出題から考えるデグレしないパフォーマンス改善
shuta13
5
560
Jamf Connect ZTNAとMDMで実現! 金融ベンチャーにおける「デバイストラスト」実例と軌跡 / Kyash Device Trust
rela1470
1
210
サイボウズフロントエンドの横断活動から考える AI時代にできること
mugi_uno
3
1.3k
Autonomous Database Serverless 技術詳細 / adb-s_technical_detail_jp
oracle4engineer
PRO
18
52k
datadog-distribution-of-opentelemetry-collector-intro
tetsuya28
0
190
[CVPR2025論文読み会] Linguistics-aware Masked Image Modelingfor Self-supervised Scene Text Recognition
s_aiueo32
0
190
Featured
See All Featured
Refactoring Trust on Your Teams (GOTO; Chicago 2020)
rmw
34
3.1k
Making Projects Easy
brettharned
117
6.3k
The Success of Rails: Ensuring Growth for the Next 100 Years
eileencodes
46
7.6k
Measuring & Analyzing Core Web Vitals
bluesmoon
9
560
Facilitating Awesome Meetings
lara
55
6.5k
The Straight Up "How To Draw Better" Workshop
denniskardys
236
140k
Side Projects
sachag
455
43k
Unsuck your backbone
ammeep
671
58k
Building Applications with DynamoDB
mza
96
6.6k
Let's Do A Bunch of Simple Stuff to Make Websites Faster
chriscoyier
507
140k
Designing for Performance
lara
610
69k
Producing Creativity
orderedlist
PRO
347
40k
Transcript
PYTFALLS
WHOAMI ▸ desenvolvedor na Jusbrasil ▸ contribui com projetos open
source como Django, Docker, OpenStack, pypy, splinter, tsuru ▸ github.com/andrewsmedina
PYTFALLS??!!
A HIDDEN OR UNSUSPECTED DANGER OR DIFFICULTY PITFALL
AN UNEXPECTED PROBLEM OR USUALLY UNPLEASANT SURPRISE GOTCHA
None
None
None
Há muito tempo, numa linguagem muito distante…
> 1 + 1
> 1 + 1 2
> 1 + “1”
> 1 + “1” “11”
> 1 + “1” “11”
> “11” - 1
> “11” - 1
> “11” - 1 10
> “11” - 1 10
> “JS” - 1
> “JS” - 1 NaN
> “JS” - 1 NaN
> Array(16).join("JS" - 2) + " Batman!"
> Array(16).join("JS" - 2) + " Batman!" "NaNNaNNaNNaNNaNNaNNaNNaNNa NNaNNaNNaNNaNNaNNaN Batman!"
None
PYTHON
É UMA LINGUAGEM INTUITIVA PYTHON
ZEN OF PYTHON PYTHON
É LEGÍVEL PYTHON
CRIADA EM 1991 PYTHON
“There should be one-- and preferably only one --obvious way
to do it.”
urllib httplib urllib3
urllib httplib urllib3
“Explicit is better than implicit.”
>>> "Oi" + u" mundo" u'Oi mundo'
>>> "Oi" + u" mundo" u'Oi mundo'
#1
Python 2
USE PYTHON3 TL;DR
#2
def append(element, to=[]): to.append(element) return to
>>> my_list = append(12) >>> print(my_list) ??? >>> my_other_list =
append(42) print(my_other_list) ???
>>> my_list = append(12) >>> print(my_list) [12] >>> my_other_list =
append(42) print(my_other_list) ???
>>> my_list = append(12) >>> print(my_list) [12] >>> my_other_list =
append(42) print(my_other_list) [12, 42]
>>> my_list = append(12) >>> print(my_list) [12] >>> my_other_list =
append(42) print(my_other_list) [12, 42]
def append(element, to=[]): to.append(element) return to
def append(element, to=None): if to is None: to = []
to.append(element) return to
def fib(n): if n <= 2: data = 1 else:
data = fib(n - 2) + fib(n - 1) return data
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]
#3
def create_multipliers(): return [lambda x : i * x for
i in range(5)]
for multiplier in create_multipliers(): print multiplier(2)
for multiplier in create_multipliers(): print multiplier(2) ? ? ? ?
for multiplier in create_multipliers(): print multiplier(2) ? (0) ? (2)
? (4) ? (6)
for multiplier in create_multipliers(): print multiplier(2) 8 8 8 8
for multiplier in create_multipliers(): print multiplier(2) 8 8 8 8
def create_multipliers(): return [lambda x : i * x for
i in range(5)]
def create_multipliers(): multipliers = [] for i in range(5): def
multiplier(x): return i * x multipliers.append(multiplier) return multipliers
def soma(x, y): return x+y
soma = lambda x, y: x+y
def soma(x, y): return x+y
def create_multipliers(): return [lambda x : i * x for
i in range(5)]
def create_multipliers(): multipliers = [] for i in range(5): def
multiplier(x): return i * x multipliers.append(multiplier) return multipliers
def create_multipliers(): return [lambda x, i=i: i * x for
i in range(5)]
#4
>>> a = 256 >>> b = 256 >>> a
is b True
>>> a = 257 >>> b = 257 >>> a
is b ???
>>> a = 257 >>> b = 257 >>> a
is b False
>>> a = 257 >>> b = 257 >>> a
is b False
>>> a = 256 >>> b = 256 >>> a
is b True
>>> help(id)
>>> help(id) id(obj, /) Return the identity of an object.
>>> a = 256 >>> id(a) 4307458704 >>> b =
256 >>> id(b) 4307458704
>>> a = 257 >>> id(257) 4312868592 >>> b =
257 >>> id(b) 4311130416
#5
# random.py import random random.randrange(100)
$ 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'
#6
*.pyc
$ find . -name "*.pyc" -delete
export PYTHONDONTWRITEBYTECODE=1
>>> import sys >>> sys.dont_write_bytecode True
$ python -B main.py
#7
>>> linguagens = {} >>> linguagens[1] = “Python” >>> linguagens[1.0]
= “Go” >>> linguagens[1] “Go”
>>> hash(1) == hash(1.0) True
#8
>>> x = [[]] * 5 >>> x [[], [],
[], [], []] >>> x[0].append(1) ????
>>> x[0].append(1) ????
>>> x[0].append(1) # [[0], [], [], [], []] ok?
>>> x[0].append(1) [[1], [1], [1], [1], [1]]
>>> x[0].append(1) [[1], [1], [1], [1], [1]]
>>> id(x[0]) 4390176008 >>> id(x[1]) 4390176008
#9
class Hero: life = 100 class Dragon(Hero): pass class Giant(Hero):
pass
>>> Hero.life, Giant.life, Dragon.life 100, 100, 100
>>> Hero.life = 10 >>> Hero.life, Giant.life, Dragon.life
>>> Hero.life = 10 >>> Hero.life, Giant.life, Dragon.life ?, ?,
?
>>> Hero.life = 10 >>> Hero.life, Giant.life, Dragon.life 10, 10,
10
>>> Giant.life = 300 >>> Hero.life, Giant.life, Dragon.life ?, ?,
?
>>> Giant.life = 300 >>> Hero.life, Giant.life, Dragon.life 10, 300,
10
>>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life ?, ?,
?
>>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life 50, 300,
50
>>> Hero.life = 50 >>> Hero.life, Giant.life, Dragon.life 50, 300,
50
Hero (life=50) Giant (life=300) Dragon
#10
class Hero: spells = []
>>> dragon = Hero() >>> dragon.spells.append(“fireball”) >>> dragon.spells [“fireball”]
>>> priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells ???
>>> priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells [“fireball”, “heal”]
>>> priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells [“fireball”, “heal”]
class Hero: spells = []
class Hero: def __init__(self): self.spells = []
>>> dragon = Hero() >>> dragon.spells.append(“fireball”) >>> dragon.spells [“fireball”] >>>
priest = Hero() >>> priest.spells.append(“heal”) >>> priest.spells [“heal”]
#DICAS
None
None
None
OBRIGADO!