Python Built-in Functions

Introduction

Python provides a wide range of built-in functions that can be used directly without needing to import any module. These functions perform various tasks, such as type conversion, mathematical operations, input/output operations, and more. Understanding these built-in functions is crucial for writing efficient and effective Python code.

Commonly Used Built-in Functions

1. Type Conversion Functions

These functions are used to convert data types.

int(): Converts a value to an integer.
float(): Converts a value to a float.
str(): Converts a value to a string.
bool(): Converts a value to a boolean.

Examples:

print(int("10"))      # Output: 10
print(float("10.5"))  # Output: 10.5
print(str(100))       # Output: "100"
print(bool(0))        # Output: False

2. Mathematical Functions

These functions perform mathematical operations.

abs(): Returns the absolute value of a number.
max(): Returns the maximum value in an iterable or among two or more arguments.
min(): Returns the minimum value in an iterable or among two or more arguments.
sum(): Returns the sum of all items in an iterable.
round(): Rounds a number to a specified number of decimal places.

Examples:

print(abs(-7))            # Output: 7
print(max(1, 5, 3, 9, 2)) # Output: 9
print(min(1, 5, 3, 9, 2)) # Output: 1
print(sum([1, 2, 3, 4]))  # Output: 10
print(round(3.14159, 2))  # Output: 3.14

3. Sequence and Collection Functions

These functions operate on sequences and collections like lists, tuples, and sets.

len(): Returns the number of items in an object.
sorted(): Returns a sorted list of the specified iterable.
reversed(): Returns an iterator that accesses the given sequence in the reverse order.
enumerate(): Returns an enumerate object containing pairs of index and value.

Examples:

print(len("Hello"))          # Output: 5
print(sorted([3, 1, 4, 1, 5])) # Output: [1, 1, 3, 4, 5]
print(list(reversed([1, 2, 3]))) # Output: [3, 2, 1]

for index, value in enumerate(["a", "b", "c"]):
    print(index, value)
# Output:
# 0 a
# 1 b
# 2 c

4. Input/Output Functions

These functions handle input and output operations.

print(): Prints to the console.
input(): Reads input from the console.

Examples:

print("Hello, World!")       # Output: Hello, World!
name = input("Enter your name: ")
print(f"Hello, {name}!")

5. Object and Type Functions

These functions are used to interact with objects and their types.

type(): Returns the type of an object.
isinstance(): Checks if an object is an instance of a specified class or type.
id(): Returns the unique identifier of an object.

Examples:

print(type(10))               # Output: <class 'int'>
print(isinstance(10, int))    # Output: True
print(id("Hello"))            # Output: (some unique identifier)

6. Miscellaneous Functions

dir(): Returns a list of valid attributes of an object.
help(): Invokes the built-in help system.
hex(): Converts an integer to a hexadecimal string.
bin(): Converts an integer to a binary string.

Examples:

print(dir(str))                # Output: (list of string methods)
help(str)                      # Output: (help information for the str class)
print(hex(255))                # Output: '0xff'
print(bin(10))                 # Output: '0b1010'

Practical Examples Using Built-in Functions

Example 1: Calculating the Average of a List

numbers = [10, 20, 30, 40, 50]
average = sum(numbers) / len(numbers)
print(f"The average is {average}")

Output:

The average is 30.0

Example 2: Converting and Formatting Strings

number = 255
hex_number = hex(number)
print(f"The hexadecimal representation of {number} is {hex_number}")

binary_number = bin(number)
print(f"The binary representation of {number} is {binary_number}")

Output:

The hexadecimal representation of 255 is 0xff
The binary representation of 255 is 0b11111111

Example 3: Sorting and Reversing a List

numbers = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]
sorted_numbers = sorted(numbers)
print(f"Sorted list: {sorted_numbers}")

reversed_numbers = list(reversed(numbers))
print(f"Reversed list: {reversed_numbers}")

Output:

Sorted list: [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9]
Reversed list: [5, 3, 5, 6, 2, 9, 5, 1, 4, 1, 3]

Example 4: Using `enumerate` in a `for` Loop

fruits = ["apple", "banana", "cherry"]
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

Output:

0: apple
1: banana
2: cherry

Example 5: Using `isinstance` and `type`

data = [10, "hello", 3.14, True]
for item in data:
    if isinstance(item, int):
        print(f"{item} is an integer")
    elif isinstance(item, str):
        print(f'"{item}" is a string')
    elif isinstance(item, float):
        print(f"{item} is a float")
    elif isinstance(item, bool):
        print(f"{item} is a boolean")

Output:

10 is an integer
"hello" is a string
3.14 is a float
True is a boolean