How to Pass Optional Parameters to a Function in Python?

Introduction

Parameters in the form of optional attributes for Python functions offer a certain degree of adaptability and engage in function calls. They permit the specifying of such functions that can be invoked with an optional number of arguments. These functions will have built-in definitions for parameters that are not passed on. Reflecting on how operators work as expressions can aid Code comprehensibility and maintainability. In this guide, we will introduce different ways to forward optional arguments to the functions in Python and the optimal approaches.

Basics of Function Parameters

Parameters of function are these inputs that are passed to a function when calling it. Parameters can be classified into two types:

The positional parameters and keyword parameters layout.

Positional parameters are specified within the function signature, and they will be set as positional arguments in its call. For example:

Output

 
Hello, Alice! How are you?

This instance shows Alice's name used as the name parameter and How are you? as the message parameter, which is based on the order of their argument's occurrence.

Variable parameters are expressed in the function header via position, whereas key parameters are highlighted in the function call by their names. They support the function argument passing will be more flexible and is especially good for a function with a greater number of parameters. For example:

Output

 
Hello, Bob! How are you?

Here, the message parameter is optional, and "How are you?" is the default value. Otherwise, the default value will be used if this is not undoubtedly specified.

1. Optional Parameters

Light parameters may have the alternative name of default parameters that have values preassigned to them mentioned in the function signature. The passed parameters will not require their assigning default value in the function call since they already have that assigned as default values.

Nonetheless, the possibility of such an override is realized during the function call upon passing a specific value to the function.

Let's take a closer look at how optional parameters work with a practical example:

Output

 
Hello, Alice! How are you?
Hello, Bob! Goodbye

Explanation

The first function call passes the message parameter by itself, while the default value of "How are you?" is taken for the message parameter. For the second function call, both parameters have been passed with the values name="David" and message="How are you today?" so they override the default "How are you?"

2. Using 'None' as a Default Parameter

In Python, 'None' could be used as a placeholder for optional parameters if the need arises. This technique is quite applicable when the default value is required to be mutable, for instance, or when it's necessary to differentiate None, which is passed explicitly, from default behavior.

Consider the following example:

Output

 
[1]
[2]
[4, 3]

Explanation

In this case, the function takes on val as a parameter and the other one an optional parameter named lst, which has a default of None. Within the function body itself, if the 'list parameter' is None, an empty list will be created using the 'list parameter' instead of None. With such a model, the list is repeatedly produced behind the function call unless it is clearly mandated.

3. Using *args and **kwargs

A function for handling arguments in Python having optional *kwargs and **args is also featured. *args provides positional arguments to a function by passing the desired number of fixed arguments, while **kwargs allows you to pass variable numbers of arguments as keyword arguments.

Here's how you can use *args and **kwargs to handle optional parameters:

Output

 
Hello, Alice, Bob! How are you?
Hello, Alice, Bob! Goodbye
Hello! Goodbye

Explanation

• The greet function is built to allow any number of names and an optional custom message using variable-argument lists with an optional length.
• *args binds together any number of positional arguments and puts them in a tuple.
• **kwargs turns kwargs into a dictionary that contains keyword arguments.
• The function checks for a 'message' in kwargs in case it is not there.
• "Do you want me to send 'a message', which by default is 'How are you?'. "
• If args is not empty, it appends names with commas in front to make a multi-greeting from personalized names.
• Example calls and outputs:
• Greet("Alice", "Bob") then replies with "Hello, Alice, Bob!" Additionally, you have to come up with something like "How are you?" in the default message.
• Say_hi("Alice", "Bob", text="So long!") responds with "Hello, Alice, Bob!" Goodbye", but as a message, we create a special one for our beloved person.
• Greet(message="Goodbye") results in "Hello!"Goodbye", when we define no names but a specific 'message'.

Best practices

1. Default Parameter Values: You should definitely use immutable objects as defaults for the parameters. Basic objects vary from None to True and False, as well as integers and strings. Thus, there is no such situation caused by using mutable default values like lists or dictionaries, as the objects are shared across multiple function calls.
2. Explicit over Implicit: Using variable names makes it easier to know the role of each parameter in the function. The latter may be achieved by using the descriptive names not only for parameters but also for functions themselves. For the usage of **kwargs, though, make sure the keywords concerned are well documented or made clear through the surrounding code context.
3. Documentation: Comprehensively note the importance of this function, its inputs, outputs, and exceptions handled. Indeed, this becomes the most critical issue when you use *args and **kwargs since the above feature can, on the other hand, cause confusion about what inputs are expected, thereby derailing the process altogether.
4. While *args and **kwargs give flexibility, overusing them will make the function interface unfocused and understanding them will be very difficult. Deploy them when absolutely necessary, for example, when integrating with third-party APIs or handling subclass methods that come with their own attributes.
5. Use Type Hints: In terms of Python, the type hints in PEP 484 (PEP stands for Python Enhancement Proposal) serve this purpose greatly. Coding in this language is then made far easier to comprehend and maintain. Even for *args and **kwargs, type hints can clarify the expected type of the arguments, e. g. , def func(*args: def area_circle(radius: float, color: str = "purple") -> None:
6. Handle None Defaults Properly: Be mindful that if a parameter that might be a list, dictionary or another mutable is set to None, it is necessary to check this within the function body and assign a new object if needed. It helps to identify and prevent them very precisely. Functions should be doing only one thing and should be short and clear. Parameter numbers, optional or not, can make the function complex and, consequently, an issue to use. Give an example of rewriting the function or use of classes, which makes complex behaviors with more parameters encapsulated.
7. Testing: Indicate adequate functional testing on the code, especially when functions have optional parameters and variable argument lists. Tests should address all the expected data types, corner cases, and input when the function accepts no arguments or when the keyword arguments do not match the expected arguments.

Conclusion

This guide demonstrates the usability of different ways and recommendations for providing optional parameters to functions in Python. Optional parameters are features that make function calls flexible and modern, giving developers a chance to create more expressive and reusable code. If they are used appropriately and the best practices are followed, the optional parameters help increase the readability and maintainability of the Python code.