Category: Python
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Pandas currency strings: Strip USD, then astype(float) and sum
I used Python Pandas to total AWS S3 payments. Data was in a CSV file. But numbers in the “Amount” column were written as “USD 12.34”. Here’s what I did:
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Python method calls: Why dict.items needs parentheses
Python gotcha: Forgetting () on method calls! Result: Error: ‘builtin_function_or_method’ object is not iterable Remember: () calls the method!
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Pandas 3.0 pd.col: Replacing lambda in loc and assign
Python Pandas 3.0 introduces pd.col, which shortens queries: Also:
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Python from import doesn’t save memory: The module still loads
Think “from modname import funcname” saves memory in Python? It doesn’t! (Lots of people think it does.) The full module still loads (see sys.modules). The only difference: “modname” isn’t in your namespace, just “funcname”. “from import” is convenient. It doesn’t save memory.
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What’s new in Pandas 3?
🎉 Pandas 3 is out! As of last week, saying “pip install pandas” or “uv add pandas” gives you the latest version. What’s new? What has changed? I’ve got a whole YouTube playlist, explaining what you need to know: https://www.youtube.com/playlist?list=PLbFHh-ZjYFwFWHVT0qeg9Jz1TBD0TlJJT
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__new__ vs __init__: Why Python constructors rarely need __new__
Heard about __new__, the constructor in Python? You can basically forget about it. It’s for advanced, unusual cases. Just use __init__! It runs automatically on every new instance. __init__ is for assigning attributes to self (what other languages call “instance variables”).
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Pandas Series and DataFrame methods: same names, column-wise results
Know Python Pandas series methods? You already know data frame methods! Same methods, applied column-wise!
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Reading multi-sheet Excel files in Pandas with sheet_name
Reading a multi-sheet Excel file into Python Pandas? Ask for a specific sheet by name or index: Get a dict of data frames with specific sheets:
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uv python pin: Changing the Python version in .python-version
Using uv? The Python version is stored in .python-version. Change it with But: uv gives an error: 3.13 is incompatible with requires-python in pyproject.toml of ‘>=3.14.’
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Learn to code with AI — not just write prompts
The AI revolution is here. Engineers at major companies are now using AI instead of writing code directly. But there’s a gap: Most developers know how to write code OR how to prompt AI, but not both. When working with real data, vague AI prompts produce code that might work on sample datasets but creates…