38. Python zip and unzip

Here are Python code snippets demonstrating how to use zip to combine iterables and how to use * for unpacking, including examples of both zipping and unzipping iterables:

1. Basic Usage of zip

This example shows how to zip two lists together.

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list1 = [1, 2, 3]
list2 = ['a', 'b', 'c']

zipped = zip(list1, list2)
zipped_list = list(zipped)
print(zipped_list)
# Output: [(1, 'a'), (2, 'b'), (3, 'c')]

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2. Unzipping with zip and *

To unzip, you can use the * operator with zip to unpack the elements back into separate lists.

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

list1, list2 = list(unzipped)
print(list1)  # Output: [1, 2, 3]
print(list2)  # Output: ['a', 'b', 'c']

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3. Zipping Multiple Iterables

You can zip more than two iterables together.

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list1 = [1, 2, 3]
list2 = ['a', 'b', 'c']
list3 = [True, False, True]

zipped = zip(list1, list2, list3)
zipped_list = list(zipped)
print(zipped_list)
# Output: [(1, 'a', True), (2, 'b', False), (3, 'c', True)]

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4. Zipping with Different Lengths

If the iterables have different lengths, zip will stop when the shortest iterable is exhausted.

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list1 = [1, 2, 3]
list2 = ['a', 'b']

zipped = zip(list1, list2)
zipped_list = list(zipped)
print(zipped_list)
# Output: [(1, 'a'), (2, 'b')]

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5. Using zip with Dictionaries

You can use zip to create dictionaries by pairing keys and values.

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keys = ['name', 'age', 'city']
values = ['Alice', 30, 'New York']

zipped_dict = dict(zip(keys, values))
print(zipped_dict)
# Output: {'name': 'Alice', 'age': 30, 'city': 'New York'}

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6. Zipping and Unzipping with Iterables of Unequal Lengths

You can handle unequal lengths by using itertools.zip_longest for zipping.

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import itertools

list1 = [1, 2, 3]
list2 = ['a', 'b']

zipped = itertools.zip_longest(list1, list2, fillvalue=None)
zipped_list = list(zipped)
print(zipped_list)
# Output: [(1, 'a'), (2, 'b'), (3, None)]

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7. Unzipping and Repacking

This shows how you can unzip a zipped iterable and then repack it.

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zipped_list = [(1, 'a'), (2, 'b'), (3, 'c')]
unzipped = zip(*zipped_list)
list1, list2 = list(unzipped)

repacked = list(zip(list1, list2))
print(repacked)
# Output: [(1, 'a'), (2, 'b'), (3, 'c')]

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8. Unpacking with * to Pass Arguments

You can use * to unpack a zipped object and pass it as arguments to a function.

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def print_info(id, name):
    print(f"ID: {id}, Name: {name}")

data = [(1, 'Alice'), (2, 'Bob'), (3, 'Charlie')]

for item in data:
    print_info(*item)
# Output:
# ID: 1, Name: Alice
# ID: 2, Name: Bob
# ID: 3, Name: Charlie

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9. Zipping with a Custom Function

You can also zip elements from multiple iterables using a custom function to combine them.

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list1 = [1, 2, 3]
list2 = ['a', 'b', 'c']

zipped = zip(list1, list2)
combined = [f"Number: {num}, Letter: {letter}" for num, letter in zipped]
print(combined)
# Output: ['Number: 1, Letter: a', 'Number: 2, Letter: b', 'Number: 3, Letter: c']

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10. Zipping and Iterating with Indices

You can use zip with enumerate to iterate over elements with indices.

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list1 = ['apple', 'banana', 'cherry']
list2 = ['red', 'yellow', 'dark red']

zipped = zip(list1, list2)
for idx, (fruit, color) in enumerate(zipped):
    print(f"{idx}: {fruit} is {color}")
# Output:
# 0: apple is red
# 1: banana is yellow
# 2: cherry is dark red

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These code snippets provide a variety of use cases for zip and unpacking with *, showing how to combine iterables, handle different lengths, and use the zipped data in different contexts.