tee

tee() creates multiple independent iterators from a single iterable, useful when you need to iterate over the same data multiple times. Python iterators can only be traversed once — once exhausted, their data is gone. tee() solves this by creating independent copies that each maintain their own position, though it buffers consumed elements in memory until all copies have advanced past them.

Creating Independent Iterators

After calling tee(), the original iterator should no longer be used directly. Each returned iterator independently yields all elements from the original source.

from itertools import tee

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

print("Iterator 1:", list(it1))
print("Iterator 2:", list(it2))

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

Multiple Independent Iterations

The second argument to tee() specifies the number of independent iterators to create. Each copy can be consumed independently for different computations.

from itertools import tee

source = range(3)
it1, it2, it3 = tee(source, 3)

print("Sum:", sum(it1))
for val in it2:
    print(f"Value: {val}")
print("Doubled:", list(2*x for x in it3))

Sum: 3
Value: 0
Value: 1
Value: 2
Doubled: [0, 2, 4]