/bad-python-code

Examples of bad python code

bad-python-code

If-Elif Hell

def func_x(num):
    if num == 1:
        return a()
    elif num == 2:
        return b()
    elif num == 3:
        return c()
    elif num == 4:
        return d()
    elif num == 5:
        return e()


# Better
def func_y(num):
    mapper = {
        1: a,
        2: b,
        3: c,
        4: d,
        5: e
    }
    return mapper[num]()

Unnecessary If-Else Boolean

def func_x(is_chubby):
    if is_chubby is True:
        return a()
    elif is_chubby is False:
        return b()


# Better
def func_y(is_chubby):
    return a() if is_chubby else b()

Less Pythonic Loop

def func_x(array):
    for i in range(len(array)):
        print(array[i])


# Better
def func_y(array):
    for item in array:
        print(item)

Returning boolean

def func_x(num):
    if num > 10:
        return True
    else:
        return False


# Better
def func_y(num):
    return num > 10

Too Many Variable Declarations

a = 1
b = 2
c = 3


# Better
a, b, c, = 1, 2, 3

Unpacking

x = [10, 20, 30]

a = x[0]
b = x[1]
c = x[2]


# Better
a, b, c, = x

If/Else Loop Without a Break

def func_x(breeds, pet):
    for breed in breeds:
        if breed == pet:
            print("I have a dog.")
    else:
        print("I don't have a dog")


func_x(["chihuahua", "jack russell"], "chihuahua")

# => I have a dog.
# => I don't have a dog


# Better
def func_y(breeds, pet):
    for breed in breeds:
        if breed == pet:
            print("I have a dog.")
            break
    else:
        print("I don't have a dog")


func_x(["chihuahua", "jack russell"], "chihuahua")
# => I have a dog.

Wildcard Imports

from typing import *


# Better
from typing import Union, Optional, OrderedDict

Context Manager

f = open("file.text", "r")
try:
    content = f.read()
finally:
    f.close()


# Better
with open("file.text", "r") as f:
    content = f.read()

Returning More than One Variable Type from Function

def func_x(param):
    if param:
        return 200, {"message": f"{param}"}
    else:
        return 400, "A useful error message"


# Better
def func_y(param):
    if param:
        return 200, {"message": f"{param}"}
    else:
        return 400, {"message": "A useful error message"}

Comparing None to a Variable

if something == None:
    print("Something is None!")


# Better
if something is None:
    print("Something is None!")

Comparing Boolean to a Variable

condition = True
if conditon == True:
    print("'Tis true!")


# Better
if condition:
    print("'This true!")

Comparing types

doggos = ["tamago", "charlie"]
if type(doggos) is list:
    print("'doggos' is a list")


# Better
if isinstance(doggos, list):
    print("'doggos' is a list")

Using Index to Return Tuple Values

def get_lego():
    return "21103", "Back to the Future Time Machine", "401", "2013"

my_lego = get_lego()
print(my_lego[0], my_lego[1], my_lego[2], my_lego[3])


# Better
from collections import namedtuple

def get_lego():
    lego = namedtuple("lego", ["serial_number", "name", "num_of_pieces", "release_year"])
    return lego("21103", "Back to the Future Time Machine", "401", "2013")

my_lego = get_lego()
print(my_lego.serial_number, my_lego.name, my_lego.num_of_pieces, my_lego.release_year)

Overusing map()

numbers = [10, 20, 30]
double_numbers = list(map(lambda num: num * 2, numbers))


# Better
numbers = [10, 20, 30]
double_numbers = [num * 2 for num in numbers]

Using Wildcard Imports

from elastic_appsearch import *


# Better
from elastic_appsearch import Client

Asking for Permission

EAFP

  • "Easier to ask for forgiveness than permission. This common Python coding style assumes the existence of valid keys or attributes and catches exceptions if the assumption proves false. This clean and fast style is characterized by the presence of many try and except statements. The technique contrasts with the LBYL style common to many other languages such as C."
  • Python Glossary
if "key" in dictionary:
    item = dictionary["key"]
else:
    item = ""


# Better
try:
    item = dictionary["key"]
except KeyError:
    item = ""

Not Using get() in a Dict to Set a Default Value

try:
    item = dictionary["key"]
except KeyError:
    item = ""


# Better
item = dictionary.get("key", "")

Masking Potential Bugs w/ Too Broad Try/Except Clauses

try:
    return do_something(my_dict[key])
except KeyError:
    return ""


# Better
try:
    value = my_dict[key]
except KeyError:
    value = ""
else:
    return value

Having Really Long Conditions in 1 Line:

if super_long_comparsion1 and super_long_comparison2:
    pass


# Better
cond1 = super_long_comparison1
cond2 = super_long_comparison2
if cond1 and cond2:
    pass