🐍 Python Mistakes Everyone Makes ❌

 

🔰 BEGINNER MISTAKES (Day 1–15)

Day 1

Using = instead of == in conditions

Day 2

Assuming print() returns a value

Day 3

Confusing is with ==

Day 4

Using mutable default arguments

def fun(x=[]): ...

Day 5

Forgetting indentation

Day 6

Thinking input() returns an integer

Day 7

Using list.sort() incorrectly

x = x.sort()

Day 8

Forgetting self in class methods

Day 9

Overwriting built-in names

list = [1, 2, 3]

Day 10

Assuming 0, "", [] are errors

Day 11

Using += thinking it creates a new object

Day 12

Not closing files

Day 13

Expecting range() to return a list

Day 14

Confusing append() vs extend()

Day 15

Misunderstanding bool("False")

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⚙️ INTERMEDIATE MISTAKES (Day 16–35)

Day 16

Modifying a list while looping over it

Day 17

Assuming list copy = deep copy

Day 18

Ignoring enumerate()

Day 19

Using global variables unnecessarily

Day 20

Not using with for file handling

Day 21

Catching exceptions too broadly

except:

Day 22

Ignoring traceback messages

Day 23

Using recursion without base case

Day 24

Thinking dict.keys() returns a list

Day 25

Wrong use of or in conditions

if x == 1 or 2:

Day 26

Using time.sleep() in async code

Day 27

Comparing floats directly

Day 28

Assuming finally won’t execute after return

Day 29

Using map() where list comprehension is clearer

Day 30

Using == None instead of is None

Day 31

Not understanding variable scope

Day 32

Confusing shallow vs deep copy

Day 33

Using list() instead of generator for large data

Day 34

Forgetting to call functions

fun

Day 35

Assuming __del__ runs immediately

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🚀 ADVANCED / PRO MISTAKES (Day 36–50)

Day 36

Misusing decorators

Day 37

Using eval() unsafely

Day 38

Blocking I/O in async programs

Day 39

Ignoring GIL assumptions

Day 40

Overusing inheritance instead of composition

Day 41

Writing unreadable one-liners

Day 42

Not using __slots__ when needed

Day 43

Mutating arguments passed to functions

Day 44

Using threads for CPU-bound tasks

Day 45

Not profiling before optimizing

Day 46

Misusing @staticmethod

Day 47

Ignoring memory leaks in long-running apps

Day 48

Overusing try-except instead of validation

Day 49

Writing code without tests

Day 50

Thinking Python is slow (without context)