How does `zip([iter(s)]*n)` Chunk a List in Python?

Zip for Chunking Lists: Understanding zip([iter(s)]n)

The zip() function is a powerful tool in Python that combines elements from multiple iterables into a list of tuples. Its usefulness extends to a variety of applications, including the splitting of lists into chunks of equal size. The expression zip([iter(s)]n) is a concise way to achieve this.

To understand how this expression works, let's break it down into its components:

• iter(s): This creates an iterator over the list s, allowing us to step through its elements one by one.
• [iter(s)]*n: This line creates a list of n copies of the iterator, effectively providing n views into the same list.
• *: The asterisk (or splat) operator unpacks the list of iterators into individual arguments for zip().

As a result, zip() is invoked with n iterators, each representing the same list. This causes zip() to pull one element from each iterator, creating a tuple. The process continues until all iterators are exhausted, resulting in a list of tuples.

To illustrate, let's consider an example with a list s = [1,2,3,4,5,6,7,8,9] and n = 3. The expression zip([iter(s)]n) would produce [(1,2,3),(4,5,6),(7,8,9)].

If we expand the expression into more verbose code, it would look like this:

x = iter(s)
y = iter(s)
z = iter(s)
chunked_list = list(zip(x, y, z))

This code produces the same result as the concise expression zip([iter(s)]n). In essence, iter() creates an iterator, [iter(s)]*n generates multiple views into the same list, and the splat operator unpacks the iterators, enabling zip() to combine elements from each one into tuples.

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