Python built-in functions are tools that are available immediately, without installing a package or importing a module. Functions such as print(), len(), type(), sum(), sorted(), and enumerate() solve common problems with concise, tested code.
This guide organizes the most useful built-ins by purpose instead of presenting an overwhelming alphabetical list. You will learn functions for input and output, types, numbers, collections, iteration, inspection, functional programming, files, and object-oriented code.
Review Python data types, functions, and loops when you need more background.
What Does Built-in Mean?
A built-in function belongs to Python’s standard execution environment. You can call it directly:
print(len("Python"))You do not need an import statement. The official built-in functions reference lists every function and its exact behavior. The standard types documentation explains the objects these functions work with.
print(): Display Values
name = "Kai"
score = 95
print(name)
print("Score:", score)
print(f"{name} scored {score} points")print() can receive several values, a custom separator, and a custom ending:
print("2026", "07", "10", sep="-")
print("Loading", end="...")
print("done")input(): Read User Input
name = input("What is your name? ")
print(f"Hello, {name}!")input() always returns a string. Convert the result when you need a number:
age = int(input("Age: "))
height = float(input("Height in meters: "))Conversion can fail, so interactive programs should validate input with exception handling.
len(): Count Items
word = "Python"
numbers = [10, 20, 30]
user = {"name": "Lina", "active": True}
print(len(word))
print(len(numbers))
print(len(user))For a dictionary, len() counts keys. For a string, it counts characters. For a list or tuple, it counts elements.
type() and isinstance(): Inspect Types
value = 42
print(type(value))
print(isinstance(value, int))Use isinstance() for validation because it supports inheritance and multiple accepted types:
if isinstance(value, (int, float)):
print("The value is numeric")Type Conversion Functions
Several built-ins create or convert values:
number = int("42")
price = float("19.95")
text = str(2026)
values = list((1, 2, 3))
coordinates = tuple([10, 20])
unique = set([1, 1, 2, 3])
record = dict(name="Ari", active=True)Conversions do not always succeed. For example, int("hello") raises ValueError. The try and except guide explains safe conversion.
Numeric Functions
abs()
print(abs(-18))
print(abs(-3.5))abs() returns the absolute value.
round()
price = 19.987
print(round(price, 2))Floating-point values have representation limitations. Do not use ordinary floats for exact financial accounting without understanding those limitations.
min() and max()
temperatures = [21, 24, 19, 27]
print(min(temperatures))
print(max(temperatures))sum()
prices = [10.5, 20.0, 7.25]
total = sum(prices)
print(total)pow() and divmod()
print(pow(2, 5))
quotient, remainder = divmod(17, 5)
print(quotient, remainder)range(): Generate Integer Sequences
for number in range(1, 6):
print(number)The stop value is excluded. You can also provide a step:
for number in range(10, 0, -2):
print(number)range() represents a sequence efficiently instead of building a full list immediately.
enumerate(): Loop with an Index
languages = ["Python", "JavaScript", "Go"]
for position, language in enumerate(languages, start=1):
print(position, language)This is clearer than maintaining a counter manually. Read the enumerate guide for more patterns.
zip(): Combine Iterables
names = ["Ana", "Ben", "Chloe"]
scores = [90, 84, 96]
for name, score in zip(names, scores):
print(f"{name}: {score}")By default, zip() stops when the shortest iterable ends. The zip guide explains strict matching and unzipping.
sorted() and reversed()
numbers = [8, 2, 10, 4]
ascending = sorted(numbers)
descending = sorted(numbers, reverse=True)
backward = list(reversed(numbers))
print(ascending)
print(descending)
print(backward)sorted() returns a new list. The original collection remains unchanged. See sort versus sorted for custom keys and stable sorting.
any() and all()
any() returns true when at least one item is truthy. all() returns true when every item is truthy.
scores = [80, 55, 91]
print(any(score >= 90 for score in scores))
print(all(score >= 50 for score in scores))These functions often make validation clearer than manual flags. The booleans guide explains truthy and falsy values.
map() and filter()
numbers = [1, 2, 3, 4]
squares = list(map(lambda number: number ** 2, numbers))
even_numbers = list(filter(lambda number: number % 2 == 0, numbers))List comprehensions are often more readable for simple transformations:
squares = [number ** 2 for number in numbers]
even_numbers = [number for number in numbers if number % 2 == 0]Choose the style that communicates the logic most clearly.
iter() and next()
iterator = iter([10, 20, 30])
print(next(iterator))
print(next(iterator))iter() creates an iterator, and next() requests the next value. When no values remain, Python raises StopIteration. A default can avoid that exception:
print(next(iterator, None))open(): Work with Files
with open("notes.txt", "r", encoding="utf-8") as file:
content = file.read()
print(content)Use a context manager so the file closes automatically. The text files guide and pathlib guide present safer file patterns.
help(), dir(), and callable()
print(callable(len))
print(dir(str)[:10])
help(str.strip)help() displays documentation, dir() lists available attributes, and callable() checks whether an object can be called.
id(), hash(), and repr()
value = "Python"
print(id(value))
print(hash(value))
print(repr(value))id() represents object identity during its lifetime. hash() supports hash-based collections. repr() returns a developer-oriented representation that is useful when debugging hidden characters.
getattr(), setattr(), and hasattr()
class User:
def __init__(self, name: str):
self.name = name
user = User("Mia")
print(hasattr(user, "name"))
print(getattr(user, "name"))
setattr(user, "active", True)
print(user.active)These functions are useful in dynamic code, but direct attribute access is clearer when the attribute is known in advance.
Common Mistakes
- Using a variable name such as
list,sum, ormaxand hiding the built-in. - Forgetting that
input()returns text. - Calling
min()ormax()on an empty sequence. - Assuming
zip()checks equal lengths automatically. - Using
round()as a complete financial precision solution. - Converting a lazy iterator to a list when streaming would be better.
- Using
eval()with untrusted input.
Avoid eval() on Untrusted Data
eval() executes a string as a Python expression. It can run dangerous code and should not be used to parse user input, JSON, or configuration files. Prefer explicit conversion functions, the json module, or a dedicated parser.
Practical Example
def summarize_scores(scores: list[float]) -> dict:
if not scores:
return {
"count": 0,
"minimum": None,
"maximum": None,
"average": None,
"all_passed": False,
}
return {
"count": len(scores),
"minimum": min(scores),
"maximum": max(scores),
"average": sum(scores) / len(scores),
"all_passed": all(score >= 60 for score in scores),
}
summary = summarize_scores([72, 88, 65, 91])
for key, value in summary.items():
print(f"{key}: {value}")This small function combines len(), min(), max(), sum(), and all() in a readable solution.
Frequently Asked Questions
Do built-in functions require an import?
No. They are available directly in normal Python code.
Can I create a variable named list or sum?
Python allows it, but doing so hides the built-in function in that scope. Use a more descriptive name.
Are map and filter better than comprehensions?
Not automatically. Choose the form that makes the transformation easiest to understand.
How can I see every built-in?
Use the official built-in functions reference or inspect the builtins module.
Conclusion
Python built-in functions provide reliable building blocks for everyday programming. Start with input, output, conversion, counting, aggregation, sorting, iteration, and validation. Then explore inspection and object-related functions as your projects grow.
The goal is not to memorize every function. Learn to recognize common problems and consult the official reference when you need a tool. Using a clear built-in is usually better than rewriting the same logic manually.
