4 Python Mistakes That Make You Look Like a Beginner (And How to Avoid Them)

1. Using Mutable Default Arguments

Mistake:

def add_item(item, items=[]):
    items.append(item)
    return items

Problem: Default mutable arguments, like lists or dictionaries, retain changes between function calls, which can lead to unexpected behavior.

Fix:

def add_item(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

2. Not Using List Comprehensions

Mistake:

result = []
for i in range(10):
    result.append(i * 2)

Problem: This approach is verbose and less efficient than it could be.

Fix:

result = [i * 2 for i in range(10)]

Explanation: List comprehensions are more Pythonic, concise, and often faster.