2.6 Built-in Functions & Methods

Python has many built-in functions and methods. Below or online you can find a overview of these functions and methods. The relevant ones are either already explained in other chapters, or after the table.

Overview

Category	Function/Method
Type & Casting	type(), int(), float(), str(), bool(), list(), tuple(), dict()
Mathematical	abs(), round(), sum(), min(), max()
Collections	len()
String Handling	.lower(), .upper(), .count(), .replace()
List Methods	.append(), .extend(), .insert(), .remove()
Dictionary Methods	.keys(), .values(), .items()

Mathematical Functions

abs(x)

Returns the absolute value of x.

print(abs(-2))     # -> 2
print(abs(3 + 4j)) # -> 5

round(number, ndigits=None)

Rounds number to ndigits decimal places (default: 0).

print(round(4.56))        # -> 5
print(round(3.14159, 2))  # -> 3.14
print(round(123456, -3))  # -> 123000

sum(iterable)

Returns the sum of the numbers in iterable.

print(sum([1, 2, 3]))                # -> 6
print(sum((), start=5))              # -> 5
print(sum({2, -2, 3, -4}, start=2))  # -> 1

min/max(iterable)

Returns the smallest/largest item in iterable.

print(min([3, 1, 4])) # -> 1
print(max([3, 1, 4])) # -> 4

Collections

len(obj)

Returns the number of elements in a collection obj.

print(len([1, 2, 3]))   # -> 3
print(len("some text")) # -> 9
print(len("a b\n"))     # -> 4
print(len([1, (2, 3)])) # -> 2

String Methods

.lower() / .upper()

Returns string in all lower-/uppercase characters.

print("Hello".lower())  # -> hello
print("Hello".upper())  # -> HELLO

.count(sub)

Counts how often sub occurs in the string.

print("banana".count("a"))  # -> 3

.replace(old, new)

Replaces the old string with a new string.

print("hello".replace("l", "x"))        # -> hexxo
print("hellllllo".replace("lll", "l"))  # -> hello

List Methods

Add Elements

Add elements by.append(value) element with value at the end of the list, extend(iterable) at the end with multiple values from iterable, or.insert(index, value) element with value at index.

l = [1]
l.append(2)
print(l)            # -> [1, 2]
l.extend([3, 4, 2])
print(l)            # -> [1, 2, 3, 4, 2]
l.insert(1, 5)
print(l)            # -> [1, 5, 2, 3, 4, 2]

Remove Elements

Remove the first element with specific value using .remove() or remove element at index using the keyword del.

l = [1, 5, 2, 3, 4, 2]
print(l.remove(2)) # -> None
print(l)           # -> [1, 5, 3, 4, 2]
print(l.pop())     # -> 2
print(l)           # -> [1, 5, 3, 4]
print(l.clear())   # -> None
print(l)           # -> [1, 5, 3, 4]

Dictionary Methods

.keys() returns a view of all keys in the dictionary. .values() returns a view of all values in the dictionary. .items() returns a view of (key, value) pairs.

d = {'a': 1, 'b': 2}
print(list(d.keys()))  # -> ['a', 'b']
print(list(d.values()))  # -> [1, 2]
print(list(d.items()))  # -> [('a', 1), ('b', 2)]