starmap

starmap() applies a function to unpacked tuples from an iterable, similar to map() but with automatic argument unpacking. This is useful when your data arrives as pre-packed argument tuples — for example, from zip(), a database query, or a CSV reader — and you want to apply a multi-argument function to each without writing an explicit loop or lambda wrapper.

Using starmap

Each element in the input iterable is unpacked as positional arguments to the function. This is equivalent to calling func(*args) for each args tuple in the iterable.

from itertools import starmap
import operator

tuples = [(2, 3), (4, 5), (6, 7)]
results = list(starmap(operator.add, tuples))
print(results)

[5, 9, 13]

starmap vs map

The key difference from the built-in map() is that map() passes each element as a single argument, while starmap() unpacks each element into separate positional arguments.

from itertools import starmap

def power(base, exp):
    return base ** exp

data = [(2, 3), (3, 2), (5, 2)]

# starmap unpacks tuples
result1 = list(starmap(power, data))
print("starmap:", result1)

# map passes tuples as single arguments
try:
    result2 = list(map(power, data))
except TypeError as e:
    print(f"map error: {e}")

starmap: [8, 9, 25]
map error: power() missing 1 required positional argument: 'exp'