What Does a Bare Asterisk (*) Mean in Python Function Parameter Lists?

Unveiling the Role of a Bare Asterisk in Parameter Lists: Exploring "Keyword-Only" Parameters

In Python, a bare asterisk (*) preceding a parameter in a function definition serves a specific purpose. This syntax signifies "keyword-only" parameters, which enforce the caller to specify argument values using named arguments.

As exemplified by the pickle.dump function:

pickle.dump(obj, file, protocol=None, *, fix_imports=True)

The parameter * is followed by fix_imports, indicating that this argument can only be assigned using the syntax fix_imports=True. This restriction ensures that the caller explicitly provides the value for this parameter, preventing potential confusion or errors.

Unlike regular parameters, which can be assigned without specifying their names (e.g., func(1, 2, 3)), keyword-only parameters require the caller to explicitly specify the argument name (e.g., func(x=1, y=2, z=3)).

If a caller attempts to assign a value to a keyword-only parameter without specifying its name, Python raises a SyntaxError. This behavior helps avoid potential ambiguity and ensures that the caller provides explicit values for all required parameters.

For further insights and documentation, refer to the Python 3 documentation or explore the reference answer provided.

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