How Does the Asterisk (*) Operator Unpack Iterables in Python Function Calls?

Asterisk Usage in Function Calls

In Python, the asterisk (*) operator serves as the "splat" operator. When used in a function call, it unpacks an iterable like a list into distinct positional arguments. This is evident in the provided code snippet:

uniqueCrossTabs = list(itertools.chain(*uniqueCrossTabs))

Here, *uniqueCrossTabs expands the nested list uniqueCrossTabs into a series of list arguments for itertools.chain(). For instance, if uniqueCrossTabs contains [[1, 2], [3, 4]], *uniqueCrossTabs translates to [1, 2, 3, 4].

This operation differs from simply passing uniqueCrossTabs without the asterisk. In the latter case, itertools.chain() receives a list of lists instead of individual list elements. Consequently, the output iterator will contain lists within its items, rather than flattened values.

An alternative approach for flattening nested iterables is to use itertools.chain.from_iterable(), which explicitly expects a single iterable of iterables. This simplifies the code to:

uniqueCrossTabs = list(itertools.chain.from_iterable(uniqueCrossTabs))

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