Itertools Advanced

Introduction

Advanced itertools patterns for complex iterator transformations.

GroupBy

import itertools

data = [("A", 1), ("A", 2), ("B", 3), ("B", 4), ("C", 5)]

for key, group in itertools.groupby(data, key=lambda x: x[0]):
    items = list(group)
    print(f"{key}: {items}")

Islice

import itertools

arr = range(10)

# First 5 elements
first5 = list(itertools.islice(arr, 5))

# Skip first 3, take next 4
subset = list(itertools.islice(arr, 3, 7))

# Infinite with islice
infinite = itertools.count()
even = itertools.islice(infinite, 0, 10, 2)  # 0, 2, 4, 6, 8

Zip Longest

import itertools

# Different lengths
a = [1, 2, 3]
b = ["a", "b"]

list(itertools.zip_longest(a, b, fillvalue=None))
# [(1, 'a'), (2, 'b'), (3, None)]

Practice Problems

1. Window sliding with islice
2. Merge overlapping intervals
3. Group by multiple keys
4. Pad sequences to same length
5. Create lazy chunking iterator