## 🧵 [Python] Why `zip(*zipped)` sometimes works twice, and sometimes doesn't?

🧵 [Python] Why zip(*zipped) sometimes works twice, and sometimes doesn't?

In Python, I recently came across this confusing behavior:

zipped = [(1, 'a'), (2, 'b'), (3, 'c')]
unzipped = zip(*zipped)

t1, t2 = map(list, unzipped)
list1, list2 = map(tuple, unzipped)  # ❌ Error: already consumed!

But in another case:

zipped = [(1, 'a'), (2, 'b'), (3, 'c')]
numbers, names = zip(*zipped)

for num, name in zip(numbers, names):
    print(f"num={num}, name={name}")  # ✅ Works

The second example works twice, even though it also uses zip(*zipped)? Why?

Let’s break it down 👇

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🔄 zip returns an iterator

unzipped = zip(*zipped)

This doesn’t give you a list or a tuple — it gives you a zip iterator, which is like a one-time-use stream. Once you read from it (like using map(), for, or list()), it's consumed and cannot be reused.

unzipped = zip(*zipped)
print(list(unzipped))  # ✅ Works
print(list(unzipped))  # ❌ Empty: already used

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💡 Solution 1: Wrap it with list() or tuple()

To reuse the result, convert the zip object to a list (or tuple) right away:

unzipped = list(zip(*zipped))

t1, t2 = map(list, unzipped)
list1, list2 = map(tuple, unzipped)  # ✅ Now it works!

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💡 Solution 2: Unpack immediately

This is what makes the second example work:

numbers, names = zip(*zipped)

Here’s what’s really happening:

• zip(*zipped) creates a one-time-use zip object.
• The unpacking (numbers, names = ...) forces the iterator to run immediately.
• The values are saved as reusable tuples.

So:

print(numbers)  # (1, 2, 3)
print(names)    # ('a', 'b', 'c')

You can reuse numbers and names as many times as you want.

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🧠 Summary

Case	Type	Reusable?
zip(*zipped)	zip iterator	❌ No
list(zip(*zipped))	list	✅ Yes
numbers, names = zip(*zipped)	tuple unpack	✅ Yes

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🍯 Analogy

Think of zip(*zipped) like a stream of water.

• If you read from it once, it's gone.
• But if you store it in a bottle (like a list or tuple), you can drink from it anytime. 😊

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Let me know if this helped you understand zip and unpacking better!
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