Built-in Functions

Python has many built-in functions that you can use. These functions are available without importing any modules. In this lesson, we will learn about a few of them. You can see a full list of built-in functions here.

Numbers

There are several functions available for working with numbers and lists of numbers. These include:

abs() - returns the absolute value of a number
round() - rounds a number to a given number of decimals
divmod() - returns both // and % in a single operation

abs(-5) # 5
round(3.14159) # 3
round(3.14159, 2) # 3.14
divmod(10, 3) # (3, 1)

Functions that take a list of numbers as an argument include:

min() - returns the smallest number in a list
max() - returns the largest number in a list
sum() - returns the sum of all numbers in a list

x = [1, 2, 3]
min(x) # 1
max(x) # 3
sum(x) # 6

Characters

The ord() and chr() functions allow you to convert a character to and from its Unicode code integer representation.

ord('a') # 97
chr(97) # 'a'

Booleans

The any() and all() functions are used to evaluate a list of booleans. Each item in the list is evaluated as a boolean, equivalent to bool() function.

bool(0) # False
bool(1) # True
bool('') # False
bool('a') # True

any([True, False, False]) # True
any([False, False, False]) # False
any([1, 0, 0]) # True
any([0, 0, 0]) # False
any(['a', '', '']) # True
any(['', '', '']) # False

all([True, False, False]) # False
all([True, True, True]) # True
all([1, 0, 0]) # False
all([1, 1, 1]) # True
all(['a', '', '']) # False
all(['a', 'a', 'a']) # True

Sequences

Several functions can be used to work with sequences. sorted() and reversed() return a new list with a changed order. The original list is not modified.

x = [3, 1, 2]
sorted(x) # [1, 2, 3]
reversed(x) # [2, 1, 3]

The enumerate() function is used to iterate over a sequence when you need both the index and the value.

x = ['a', 'b', 'c', 'c', 'b', 'a']
for i, v in enumerate(x):
    print(i, v) 
    if i != 0 and v == x[i-1]:
        print("two of the same value in a row")

# 0 a
# 1 b
# 2 c
# 3 c
# two of the same value in a row
# 4 b
# 5 a

The zip() function is used to iterate over multiple sequences at the same time.

x = ['a', 'b', 'c']
y = [1, 2, 3]
for i, j in zip(x, y):
    print(i, j)

# a 1
# b 2
# c 3

The map() function is used to apply a function to each item in a sequence.

x = ["1", "2", "3"]
y = list(map(int , x)) # [1, 2, 3]

Exercise

Given two lists of numbers called secret and key, use the following steps to decode the message.