How to Define and Use Python Functions with Different Argument Types

The concept of functions is pivotal in Python programming. Functions allow you to encapsulate specific tasks, making your code modular and reusable across different parts of your Python programs. This article aims to illustrate how to define functions in Python and how to effectively pass arguments to these functions.

Table of Contents

1. How to Define Python Function.

In Python, you define a function using the `def` keyword followed by the function name and its parameters enclosed within parentheses.

If the function returns a value, you can specify it using the `return` keyword. It’s worth noting that if no return value is specified, Python automatically returns `None`.

The function definition is terminated with a colon `:`. Below is the Python function definition syntax.

def function_name(arg1, arg2 [, ...]):
    function_statement
    [return value]

Below is an example of defining a `login` function which prints login status information:

def login(username, password):
    if(username=='hello') and (password == 'hello'):
        print("Login Success!")
    else:
        print("Login Failed!")

To define this function in the terminal, type in the command followed by pressing the enter key to complete the definition. Then, you can invoke the `login` function with appropriate arguments.

>>> def login(username, password):
...     if(username=='hello') and (password == 'hello'):
...         print("Login Success!")
...     else:
...         print("Login Failed!")
...
>>> login('hello','hello')
Login Success!

2. Examples of Python Function Arguments.

2.1 Default Argument Values.

Function arguments can have default values, which are specified in the function definition. Here’s an example using string data as the default argument value:

def login(username = 'admin', password = 'hello'):
    if(username=='hello') and (password == 'hello'):
        print("Login Success!")
    else:
        print("Login Failed!")

You can then call this function with fewer arguments, and the default values will be used for the unspecified ones:

>>> login('hello')
Login Success!

2.2 Argument Values as List.

Arguments can be of different types, including lists or tuples:

def login(usernameList = [], password = 'hello'):
    username = usernameList[0]
    if(username=='hello') and (password == 'hello'):
        print("Login Success!")
    else:
        print("Login Failed!")

You can pass a list as an argument:

>>> login(['hello','admin'])
Login Success!

2.3 Variable (none-fix) Length Arguments.

Using `*` allows you to define variable-length arguments, similar to a list or tuple:

def login(*usernamepassword):
    username = usernamepassword[0]
    password = usernamepassword[1]
    if(username=='hello') and (password == 'hello'):
        print("Login Success!")
    else:
        print("Login Failed!")

You can then call this function with any number of arguments, it will treat the input parameter as a list.

>>> login('hello','hello')
Login Success!

2.4 Argument Values as Dictionary.

You can pass a dictionary object as an argument using `**`:

def loginWithDictArguments(**upDict):
    username = upDict.get('username', '')
    password = upDict.get('password', '')
    email = upDict.get('email', '')
    if(username=='hello') and (password=='hello'):
        print('Login Success. Your email is ' + email)
    else:
        print('Login fail. Your email is ' + email)  

>>> loginWithDictArguments(username='hello', password='hello', email='[email protected]')
Login Success. Your email is [email protected]

3. Conclusion.

These examples showcase the versatility of function arguments in Python, allowing you to handle various scenarios effectively.