12 Python Habits That Scream ‘Junior Developer’ (And How to Fix Them)

From verbose loops to mutable defaults - the subtle mistakes that separate working code from professional Python

Even after months (or years) of coding in Python, subtle mistakes still creep in. They don’t always crash your program — but they silently reveal inexperience. The difference between “code that works” and “code that feels professional” is often in these small habits.

I’ve hit many of these traps myself while working on production pipelines, APIs, and data-heavy systems. Over time, I learned the Pythonic fixes — and trust me, they make your code cleaner, faster, and more maintainable.

Here are 12 mistakes I’ve made (and seen others make), and what I wish I had known earlier.

1. Not Understanding Truthiness (Testing len() Instead of Bool Context)

Python has built-in truthiness rules. Use them.

The Rookie Way:

# Unnecessarily verbose
if len(my_list) == 0:
    print("Empty")

if len(my_list) > 0:
    print("Has items")

if my_dict == {}:
    print("Empty dict")