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Python Defining and Calling Functions

Defining Functions

A function in Python is defined using the def keyword, followed by the function name, parentheses, and a colon. The code block within every function starts with an indentation and contains the function body.

Basic Function Definition

def function_name(parameters):
    """Docstring explaining the function."""
    # Function body
    return value


  • function_name: The name of the function.
  • parameters: Optional. Parameters that the function takes. They are also called arguments.
  • Docstring: Optional. A string that describes what the function does.
  • Function body: The block of code that performs the function’s task.
  • return: Optional. Specifies what the function returns. If not specified, the function returns None by default.

Example of Defining a Function

def greet(name):
    """This function greets the person whose name is passed as an argument."""
    print(f"Hello, {name}!")


Calling Functions

A function is called by using its name followed by parentheses. If the function takes parameters, you pass the arguments inside the parentheses.

Basic Function Call

greet("Alice")  # Output: Hello, Alice!

Examples of Defining and Calling Functions

Function with No Parameters

def say_hello():
    """This function prints a hello message."""
    print("Hello, world!")

# Calling the function
say_hello()  # Output: Hello, world!

Function with Parameters

def add(a, b):
    """This function returns the sum of two numbers."""
    return a + b

# Calling the function
result = add(3, 5)
print(result)  # Output: 8

Function with Default Parameters

def greet(name="Guest"):
    """This function greets the person whose name is passed as an argument, or 'Guest' if no name is provided."""
    print(f"Hello, {name}!")

# Calling the function
greet("Alice")  # Output: Hello, Alice!
greet()         # Output: Hello, Guest!


Function with Variable-Length Arguments

Sometimes, you might want to pass a variable number of arguments to a function. This can be achieved using *args for non-keyword arguments and **kwargs for keyword arguments.

def print_numbers(*args): """This function prints all the numbers passed to it.""" for num in args: print(num) # Calling the function print_numbers(1, 2, 3, 4) # Output: # 1 # 2 # 3 # 4

def print_info(**kwargs):
 """This function prints the keyword arguments passed to it."""
        for key, value in kwargs.items():
            print(f"{key}: {value}")
# Calling the function
print_info(name="Alice", age=30, city="New York")  
# Output:
# name: Alice
# age: 30
# city: New York


Return Statement

A function can return a value using the return statement. If a return statement is not used, the function returns None.

Function with a Return Value

def multiply(a, b):
    """This function returns the product of two numbers."""
    return a * b

# Calling the function
result = multiply(4, 5)
print(result)  # Output: 20


Lambda Functions

For simple, small functions, you can use lambda functions (also known as anonymous functions).

Lambda Function Example

# A lambda function that adds two numbers
add = lambda x, y: x + y

# Calling the lambda function
result = add(3, 5)
print(result)  # Output: 8


Functions in Python are a fundamental part of the language, allowing for reusable and organized code. By understanding how to define and call functions, you can write more efficient and maintainable code.















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