The Python Trap That Catches EVERY Beginner! #shorts

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Taught by Celeste AI - AI Coding Coach
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Can you guess what this Python code prints? python: def add_item(item, items=[]): items.append(item) return items print(add_item(1)) print(add_item(2)) This is one of Python's most famous gotchas - the mutable default argument trap! Default mutable arguments like lists and dictionaries are created ONCE when the function is defined, not each time it's called. This means the same list is shared between all function calls! The fix? Use None as the default and create a new list inside the function: def add_item(item, items=None): if items is None: items = [] items.append(item) return items Follow @GoCelesteAI for more coding quizzes and programming tips! #python #programming #coding #developer #programmer #tech #codingquiz #pythontips #learnpython #softwareengineering #codetest #interviewquestions #shorts python, programming, coding, developer, programmer, tech, codingquiz, pythontips, learnpython, softwareengineering, codetest, interviewquestions, shorts, mutable default arguments, python gotchas, python bugs, python interview, coding challenge
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Duration

0:46

Published

January 18, 2026

Added to Codegiz

March 15, 2026

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