🔁 Understanding zip(*zip(x, y)) in Python

How zip can both pack and unpack like magic!

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🧩 What's zip in Python?

The built-in zip() function pairs up elements from multiple iterables.

x = [1, 2, 3]
y = [4, 5, 6]
zipped = zip(x, y)
print(list(zipped))  # [(1, 4), (2, 5), (3, 6)]

Now here’s something interesting:

x2, y2 = zip(*zip(x, y))
print(x2)  # (1, 2, 3)
print(y2)  # (4, 5, 6)

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🔍 What’s happening here?

Let’s break it down.

🔹 zip(x, y)

Combines the elements pair-wise:

[(1, 4), (2, 5), (3, 6)]

🔹 *zip(x, y) → Unpacking

The asterisk * unpacks the list of pairs into separate arguments:

zip((1, 4), (2, 5), (3, 6))

So it's like we're zipping the columns of the original pair list.

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💡 Why is it useful?

It transposes the data — rows become columns:

zip(*[(1, 4), (2, 5), (3, 6)]) 
→ zip((1, 4), (2, 5), (3, 6)) 
→ [(1, 2, 3), (4, 5, 6)]

You get:

x2 = (1, 2, 3)
y2 = (4, 5, 6)

So this line:

x2, y2 = zip(*zip(x, y))

is a way to unzip or reverse the original zip operation.

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✅ Final check

x == list(x2) and y == list(y2)  # True

Everything matches — zip/unzip is successful!

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📖 Official Python Docs

You can find this trick (and more like it) in the official Python zip() documentation here:

🔗 https://docs.python.org/3/library/functions.html#zip

It even includes this line:

“An idiom for clustering a data series into n-length groups using zip(*[iter(s)]*n).”

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🧠 TL;DR

Expression	Meaning
zip(x, y)	Combine x and y into pairs
zip(*zip(x, y))	Reverse the zip — unzip it!
* operator	Unpacks zipped list into arguments

This is one of those Pythonic idioms that feels a bit magical — but now you know the logic behind it 🔥