what is function in python?

In Python, a function is a block of code that performs a specific task and can be called from other parts of the program. Functions help to break down large programs into smaller, more manageable pieces, and they can be reused in different parts of the program.

Functions are defined using the def keyword, followed by the function name and a set of parentheses. The parentheses can optionally contain parameters, which are values that are passed to the function when it is called. The function body is indented and contains the code that is executed when the function is called.

Here's a simple example of a function that takes two numbers as parameters and returns their sum:

python
def add_numbers(x, y):
    return x + y

This function takes two parameters (x and y), and returns their sum using the return keyword. To call this function, you would simply pass in the values for x and y, like this:

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result = add_numbers(5, 10)
print(result) # Output: 15

Functions can also have default parameter values, which are used if the caller doesn't provide a value for that parameter. For example:

python
def greet(name="World"):
    print("Hello, " + name + "!")

In this example, the greet() function has a default parameter value of "World". If no value is provided for name, the function will use the default value. To call this function with the default value, you can simply do:

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greet() # Output: Hello, World!

Functions can be very powerful in Python, and they are used extensively in many programs. By using functions, you can create code that is easier to read, easier to test, and easier to maintain.