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.

```python 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.

```python 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'

Exercises¶

Exercise 1. Use starmap with operator.mul to compute the element-wise product of two lists. For example, given [(2, 3), (4, 5), (6, 7)], return [6, 20, 42].

Exercise 2. Use starmap to call str.format on a list of (template, value) pairs. For example, given [("Hello, {}!", "Alice"), ("Score: {}", 95), ("{} items", 3)], return ["Hello, Alice!", "Score: 95", "3 items"].

Exercise 3. Write a function apply_functions that takes a list of (function, argument) pairs and uses starmap to apply each function to its argument. For example, given [(abs, -5), (str.upper, "hello"), (len, [1, 2, 3])], return [5, "HELLO", 3].