Python itertools.tee Function

The itertools.tee function in Python’s itertools module returns multiple independent iterators (or "tees") from a single input iterable. It is useful when you need to iterate over the same iterable in parallel, without consuming it.

Table of Contents

1. Introduction
2. itertools.tee Function Syntax
3. Examples
   • Basic Usage
   • Using Multiple Tees
   • Iterating in Parallel
   • Combining with Other Itertools Functions
4. Real-World Use Case
5. Conclusion

Introduction

The itertools.tee function creates multiple independent iterators from a single input iterable. This allows you to iterate over the same sequence multiple times simultaneously, without having to store the entire sequence in memory.

itertools.tee Function Syntax

Here is how you use the itertools.tee function:

import itertools

iterators = itertools.tee(iterable, n=2)

Parameters:

• iterable: The input iterable to be duplicated.
• n: Optional. The number of independent iterators to return (default is 2).

Returns:

• A tuple of n independent iterators.

Examples

Basic Usage

Create two independent iterators from a single list.

Example

import itertools

data = [1, 2, 3, 4, 5]
it1, it2 = itertools.tee(data)

print(list(it1))  # Output: [1, 2, 3, 4, 5]
print(list(it2))  # Output: [1, 2, 3, 4, 5]

Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

Using Multiple Tees

Create three independent iterators from a single list.

Example

import itertools

data = [1, 2, 3, 4, 5]
it1, it2, it3 = itertools.tee(data, 3)

print(list(it1))  # Output: [1, 2, 3, 4, 5]
print(list(it2))  # Output: [1, 2, 3, 4, 5]
print(list(it3))  # Output: [1, 2, 3, 4, 5]

Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

Iterating in Parallel

Iterate over the same sequence in parallel using two iterators.

Example

import itertools

data = [1, 2, 3, 4, 5]
it1, it2 = itertools.tee(data)

for x, y in zip(it1, it2):
    print(f"it1: {x}, it2: {y}")

Output:

it1: 1, it2: 1
it1: 2, it2: 2
it1: 3, it2: 3
it1: 4, it2: 4
it1: 5, it2: 5

Combining with Other Itertools Functions

Combine tee with filter to create multiple filtered iterators.

Example

import itertools

data = range(10)
it1, it2 = itertools.tee(data)

evens = filter(lambda x: x % 2 == 0, it1)
odds = filter(lambda x: x % 2 != 0, it2)

print(list(evens))  # Output: [0, 2, 4, 6, 8]
print(list(odds))   # Output: [1, 3, 5, 7, 9]

Output:

[0, 2, 4, 6, 8]
[1, 3, 5, 7, 9]

Real-World Use Case

Splitting an Iterator for Multiple Passes

Use tee to split an iterator for multiple passes over the data.

Example

import itertools

def process(data):
    it1, it2 = itertools.tee(data)
    print("First pass:")
    for item in it1:
        print(item)
    print("Second pass:")
    for item in it2:
        print(item)

data = [1, 2, 3, 4, 5]
process(data)

Output:

First pass:
1
2
3
4
5
Second pass:
1
2
3
4
5

Conclusion

The itertools.tee function is used for creating multiple independent iterators from a single input iterable. It allows you to iterate over the same sequence in parallel, making it useful for various data processing tasks that require multiple passes over the data.