What are Python's built-in math and utility functions?

Short answer

Python includes many built-in functions for common tasks. len() returns the length of a collection, range() generates sequences of numbers, enumerate() adds indices, zip() pairs iterables, and map()/filter() apply transformations and predicates.

How it works

# len
print(len("hello"))          # 5
print(len([1, 2, 3]))        # 3

# range
print(list(range(3)))        # [0, 1, 2]
print(list(range(1, 6, 2)))  # [1, 3, 5]

# enumerate
for idx, val in enumerate(["a", "b"]):
    print(idx, val)

# zip
keys = ["x", "y"]
vals = [10, 20]
print(dict(zip(keys, vals)))  # {'x': 10, 'y': 20}

Example

Using map() and filter():

numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x ** 2, numbers))
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(squared)  # [1, 4, 9, 16, 25]
print(evens)    # [2, 4]

Why it matters

Built-in functions are implemented in C and are highly optimized. Using them instead of manual loops makes code shorter, faster, and more Pythonic.

Common issues

• map() and filter() return iterators in Python 3; wrap them in list() if you need a list.
• zip() stops at the shortest input; use itertools.zip_longest() to pad shorter iterables.
• len() does not work on iterators because they do not support random access.