What counts as a Python built-in function?

Built-in functions are the names available in every Python program without importing anything, because they live in the builtins module that is always in scope. Examples include print, len, range, sorted, and isinstance. Type constructors like int, str, list, and dict are also exposed as built-ins and behave like functions.

What is the difference between map and a list comprehension?

map(func, iterable) returns a lazy iterator that applies func to each item, computing values only as you consume them. A list comprehension builds a full list immediately and can include filtering and complex expressions inline. Use map for a single function over an iterable in a streaming pipeline; a comprehension is usually clearer for anything more involved.

When should I use enumerate instead of range(len(x))?

enumerate(iterable) yields index and item pairs directly, so you avoid indexing the sequence by hand. It is clearer and works on any iterable, not just sequences that support len and subscripting. You can also pass a start value, like enumerate(items, 1), to begin counting from one.

What does sorted return and how is it different from list.sort?

sorted(iterable) returns a new sorted list and leaves the input untouched, accepting any iterable. The list.sort() method sorts a list in place and returns None. Both take key and reverse arguments. Use sorted when you need a new list or are sorting a non-list iterable; use list.sort when you own the list and want to avoid a copy.

Is this the complete set of Python built-ins?

It covers the built-in functions and the common built-in type constructors you use in everyday Python 3 code. A few rarely-used names and the full set of built-in exceptions are not listed. For exhaustive, version-precise detail consult the official Python documentation's Built-in Functions page.

What is the Python Built-in Functions Reference?

Searchable reference for all Python 3 built-in functions — type conversion, iterables, math, I/O, and introspection — with each function's signature, return type, and a concise description. It runs free in your browser on Gera Tools, with nothing uploaded.

Python Built-in Functions Reference

Name: Python Built-in Functions Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Python’s built-in functions are always available — no import needed — because they live in the builtins module that is in scope everywhere. They cover type conversion, iteration, math, I/O, and introspection. This is a searchable offline reference with signatures and return types.

How it works

Each entry lists the call signature and the return type so you can see at a glance what a function expects and produces:

Type constructors (int, str, list, dict, set) build or convert values and are exposed as callables.
Iterable tools (map, filter, zip, enumerate, sorted, reversed) transform sequences; several return lazy iterators rather than lists.
Math (abs, sum, min, max, round, pow, divmod) operate on numbers.
Introspection (type, isinstance, getattr, dir, vars, hasattr) inspect objects at runtime.
I/O and execution (print, input, open, repr, eval) interact with the outside world.

Example

enumerate and zip are the idiomatic way to iterate:

for i, (name, score) in enumerate(zip(names, scores), start=1):
    print(i, name, score)

map/filter return lazy iterators — wrap in list(...) to materialize.

Frequently confused pairs

Some built-ins look similar but have important behavioral differences. These are the pairs that trip up Python learners most often:

sorted vs list.sort

sorted(iterable) returns a new sorted list from any iterable, leaving the original intact. list.sort() sorts the list in place and returns None. Use sorted when you need the result assigned to a variable, or when you are sorting a tuple, set, or other non-list iterable. Use .sort() when you own the list and want to avoid creating a copy.

scores = [5, 3, 8, 1]
ranked = sorted(scores)    # scores unchanged; ranked is a new list
scores.sort()              # scores itself is now sorted; returns None

map vs list comprehension

map(func, iterable) applies a single function to every item and returns a lazy iterator. A list comprehension builds the full list at once and can include conditions, multiple variables, and arbitrary expressions. map is concise for a simple function call; a comprehension is usually more readable for anything more complex.

doubles = list(map(lambda x: x * 2, numbers))    # map + lambda
doubles = [x * 2 for x in numbers]               # cleaner comprehension

any vs all

any(iterable) returns True if at least one element is truthy; all(iterable) returns True only if every element is truthy. Both short-circuit and work with lazy iterables.

isinstance vs type

type(obj) is int is a strict identity check — it returns False for subclasses. isinstance(obj, int) returns True for instances of int and any subclass of int. Prefer isinstance in most code, especially when working with inheritance hierarchies.

Notes

Many iterable functions (map, filter, zip, range, reversed) return lazy iterators in Python 3 — they compute values only as consumed.
sorted returns a new list; list.sort() sorts in place and returns None.
round uses banker’s rounding (round half to even), so round(0.5) is 0 and round(1.5) is 2.
This reference covers the common built-ins, not every name or built-in exception. Consult the official docs for version-exact behavior.