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
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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)]
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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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