Tag: Python
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Python *args: Collecting positional arguments into a tuple
Classic use of Python’s *args: Invoke it with separate int arguments: and *not* with a list containing ints:
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Python *args: Accepting any number of positional arguments
Want your Python function to take any number of positional args? Use *args: – Can be any name, but args is traditional– The * is only in the function definition– It’s a tuple– Don’t grab elements by index; iterate over them– It might be empty– Pronounce it “splat args”
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Positional vs keyword arguments in Python function calls
How are arguments assigned to parameters when calling a Python function? There are two ways: – Positional, based on order– Keyword, i.e., name=value, assigned by name Want to mix and match? Fine, but all positional must come before all keyword:
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Python 3.15 lazy imports: Deferring module load until first use
Every import in Python executes the module, from start to finish. Meaning? Big modules slow down your program’s startup time. Coming in Python 3.15 this October: “lazy import”, which delays the load until a name is used: lazy import MODULElazy from MODULE import NAME
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Python dict keys: Why custom objects work but lists don’t
Mutable builtins in Python cannot be dict keys. But your (mutable) classes can!
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Multi-line f-strings in Python: Triple quotes with interpolation
Want to include a dynamic value in a multi-line Python string? That would require both an f-string and a triple-quoted string. Good news: Python supports this!
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Python multiline strings: \n versus triple quotes
Want to include a newline in a Python string? Use \n: That’s fine for small strings. But for longer ones, use a triple-quoted string: BTW, the created strings are the same:
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Python string quotes: Handling an apostrophe inside a string
A classic Python mistake: What’s wrong with this code? The string uses ” as delimiters. But it also contains a ‘ inside. Solutions:
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Reading binary files in Python: Use ‘rb’ mode to get bytes
Want to read a non-text file with Python? Specify “rb”, for “read binary,” to avoid errors. What is t? A *byte* string, not a regular text string.
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functools.total_ordering: Define two comparison methods, get six
Python tip: Don’t write all 6 comparison methods! Define __eq__ and __lt__, then add @total_ordering: You get >, >=, <= for free!