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.

3. Misunderstanding Python’s Scope Rules (LEGB Rule)

Mistake:

x = 10

def example():
    print(x)
    x = 5
example()

Problem: This raises an UnboundLocalError because Python considers x inside example() as a local variable due to the assignment.

Fix:

x = 10

def example():
    global x
    print(x)
    x = 5
example()
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4. Using print() for Debugging Instead of Proper Debugging Tools

Mistake:

def calculate(x):
    print(f"Debug: x = {x}")
    return x * 2

result = calculate(5)

Problem: Relying on print() statements for debugging can clutter code and is less efficient.

Fix:

def calculate(x):
    return x * 2

result = calculate(5)
# Use a debugger for inspection
import pdb; pdb.set_trace()
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