5 Python Mistakes to Avoid for Efficient Coding

5 Python mistakes that slow down your code: 1. Using mutable default arguments If your function has `def func(items=[])`, that list persists across all calls. Every Python dev has debugged this at 2am. Use `None` and initialize inside the function. 2. Not using list comprehensions Writing a loop with .append() when a comprehension would be one line and faster. Comprehensions aren't just shorter - they're optimized at the bytecode level. 3. Forgetting context managers for resources Still seeing `f = open('file.txt')` and `f.close()` in production code. If an exception happens between those lines, you leak the file handle. Use `with open()` - that's what it's for. 4. Using `==` to check None, True, False `if x == None` works but `if x is None` is the correct way. Identity checks are faster and handle edge cases better. Same for boolean singletons. 5. No `if __name__ == "__main__":` guard Your script runs differently when imported vs executed directly. Guard your main execution code or your tests will have side effects. 5 Python tips that improved my code: 1. F-strings for everything If you're still using .format() or % formatting, stop. f"Hello {name}" is faster, cleaner, and reads naturally. 2. enumerate() instead of range(len()) `for i, item in enumerate(items)` is more Pythonic than manually tracking indexes. You get both the value and position. 3. dict.get() with sensible defaults `config.get('timeout', 30)` handles missing keys gracefully. No try/except blocks, no KeyError debugging. 4. Multiple assignment and unpacking Python lets you swap variables without a temp: `x, y = y, x`. Unpack lists: `first, *rest = items`. Use it. 5. Pathlib instead of os.path `Path('data') / 'file.txt'` is more intuitive than os.path.join(). It's chainable, handles Windows/Unix differences, and reads like plain English. Most Python mistakes aren't about skill - they're about not knowing the language idioms. Once you learn them, your code gets cleaner and you stop writing Java in Python syntax. #python #engineering #development

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