# import itertools

**[import itertools](https://docs.python.org/3/library/itertools.html)** is a Python import that provides efficient iteration tools: combinations, permutations, chaining iterables, and infinite counters. Use these for combinatorics and lazy evaluation.

## Example

```python
# Python
# description: combinations, permutations, infinite count

import itertools

# Combinations (no order)
combos = itertools.combinations("ABC", 2)
print(list(combos))  # [('A', 'B'), ('A', 'C'), ('B', 'C')]

# Permutations (all orderings)
perms = itertools.permutations("AB", 2)
print(list(perms))  # [('A', 'B'), ('B', 'A')]

# Chain multiple iterables
numbers = itertools.chain([1, 2], [3, 4], [5])
print(list(numbers))  # [1, 2, 3, 4, 5]

# Infinite counter
counter = itertools.count(start=10, step=2)
print([next(counter) for _ in range(5)])  # [10, 12, 14, 16, 18]

# Repeat value
repeated = itertools.repeat("x", times=3)
print(list(repeated))  # ['x', 'x', 'x']

# Cycle through iterable
cycle = itertools.cycle([1, 2, 3])
print([next(cycle) for _ in range(7)])  # [1, 2, 3, 1, 2, 3, 1]
```

## Common functions

- `itertools.combinations(iterable, r)`: r-length combinations
- `itertools.permutations(iterable, r)`: r-length permutations
- `itertools.product(*iterables)`: Cartesian product
- `itertools.chain(*iterables)`: concatenate iterables
- `itertools.count(start, step)`: infinite counter
- `itertools.repeat(value, times)`: repeat value
- `itertools.cycle(iterable)`: cycle indefinitely
- `itertools.islice(iterable, stop)`: lazy slice