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(), complex() |
| Mathematical | abs(), round(), sum(), min(), max() |
| Iterables & Sequences | len(), sorted(), reversed(), enumerate() |
| String Handling | .lower(), .upper(), .strip(), .split(), .join(), .replace(), .count() |
| List Methods | .append(), .extend(), .insert(), .remove(), .pop() |
| Dictionary Methods | .keys(), .values(), .items() |
Mathematical Functions
abs(x)
Returns the absolute value of x.
print(abs(-2)) # -> 2
print(abs(3 + 4j)) # -> 5round(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)) # -> 123000sum(iterable)
Returns the sum of iterable of numbers.
print(sum([1, 2, 3])) # -> 6min/max(iterable, key=None)
Returns the smallest/largest item in iterable or the default if empty. The key can take a function that will be executed for each element to determine its value.
print(min([3, 1, 4])) # -> 1
print(max([3, 1, 4])) # -> 4
print(min(["apple", "banana"], key=len)) # -> apple
print(max(["apple", "banana"], key=len)) # -> banana
people = [{"name": "Andreas", "size": 181}, {"name": "Tom", "size": 168}]
print(min(people, key=lambda x: x["size"])) # -> {'name': 'Tom', 'size': 168}
print(max(people, key=lambda x: x["size"])) # -> {'name': 'Andreas', 'size': 181}Collections
len(obj)
Returns the number of items 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)])) # -> 2sorted(iterable, key=None, reverse=False)
Returns a new sorted list from iterable. Default is ascending (smallest to largest), but you can reverse it. The key can take a function that will be executed for each element to determine the value that will be used for sorting. You can also sort a existing list in place with the method .sort().
print(sorted([3, 1, 2])) # -> [1, 2, 3]
people = [{"name": "Andreas", "size": 181}, {"name": "Tom", "size": 168}]
print(sorted(people, key=lambda x: x["size"])) # -> [{'name': 'Tom', 'size': 168}, {'name': 'Andreas', 'size': 181}]reversed(iterable)
Returns an iterator thats the reversed order of the initial iterable. You can also reverse a existing list in place with the method .reverse().
print(list(reversed([1, 2, 3]))) # -> [3, 2, 1]enumerate(iterable, start=0)
Returns an iterator with (index, value) pairs from iterable. You can set a start value for indexing (default: 0)
print(list(enumerate([33, 66, 99]))) # -> [(0, 33), (1, 66), (2, 99)]
print(list(enumerate("abc", start=10))) # -> [(10, 'a'), (11, 'b'), (12, 'c')]String Methods
.lower() / .upper()
Returns string in all lower-/uppercase characters.
print("Hello".lower()) # -> hello
print("Hello".upper()) # -> HELLO.strip(character="")
Returns a string without all characters at the start end end of the initial string. By default removes all whitespace type characters. Everything between the two outer most characters that are not in the characters to remove will be kept. You can use .lstrip()/.rstrip() to only remove from the start/end.
print(" \n test message \n".strip()) # -> test message
print(" \n test message \n".lstrip()) # -> test message \n
print(" \n test message \n".rstrip()) # -> \n test message
print(" \n, ,,;; test, message,, ,;; \n".strip(" \n,;")) # -> test message.split(sep=" ")
Splits a string into a list. Whenever sep occurs, a new element will start. Default sep is a space ” “.
print("hello world text".split()) # -> ['hello', 'world', 'text']
print("some | random | string".split(sep=" | ")) # -> ['some', 'random', 'string'].join(iterable)
Joins string elements from an iterable with the string as separator.
print("".join(["a", "b", "c"])) # -> abc
print("-".join(["a", "b", "c"])) # -> a-b-c.replace(old, new)
Replaces the old string with a new string.
print("hello".replace("l", "x")) # -> hexxo
print("hellllllo".replace("lll", "l")) # -> hello.count(sub)
Counts how often sub occurs.
print("banana".count("a")) # -> 3List 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() first element with specific value, .pop() (remove and return) element at index, or .clear() the whole list.
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)]