Let me start with a fact: Every function returns a value when called.
Well, I don't know about you, but I was surprised to know about it in the first place!
Let's see an example to prove my point:
Welcome to my blog post None
Did you see that? When I called the function, it has returned the special type None. The variable post stores it and prints it out in the second line.
Now, we can explicitly return a value from a function by using the return keyword.
- The return statement includes a return keyword followed by an expression.
- An expression is a set of conditions which produces a value.
- So, the return statement can contain an expression or an explicit value to be returned.
- A return statement also ends the function execution. This means that any statements inside a function following the return statement will not be executed.
- Take a note that return statement cannot be used outside a function.
Let's code a few examples:
1) Single return statement
As you can see in this example, we have given an expression which returns the product of given two numbers.
Here, an explicit value is specified in multiple return statements.
This example returns dynamic values in a tuple based on the given argument.
Arguments and parameters in functions
In general, the term parameters and arguments are being used interchangeably.
Although, with respect to a function:
- parameters are the variables listed inside the parentheses in the function definition.
- arguments are the values that are sent to the function when it is called.
It turns out that it's possible to define functions with various types of arguments in python. And there are three types of arguments/parameters, which can be combined.
The most useful type of argument is to specify a default value for one or more arguments, inside the parenthesis of a function definition. This creates a function that is flexible to use. Because this function can be called with fewer arguments than it is defined to allow.
Let's look at an example:
You have 120 minutes! Let's watch a action type web series You have 150 minutes! Let's watch a thriller type web series You have 200 minutes! Let's watch a horror type movie
This function is called in several ways:
- giving only the mandatory argument: popcorn_time(120)
- giving one of the optional arguments: popcorn_time(150, 'thriller')
- or even giving all arguments: popcorn_time(200, 'horror', 'movie')
2) Keyword Arguments
Functions can also be called using keyword arguments of the form kwarg=value.
For instance, consider the above example of popcorn_time, function which accepts one required argument(time) and two optional arguments(genre, watch). This function can be called in any of the following ways:
But take a note that, the following function calls would be invalid:
3) Special parameters
By default, arguments may be passed to a Python function either by position or explicitly by keyword. For readability and performance, we can restrict the way arguments can be passed
So, a developer needs to look at the function definition to determine if items are passed by position, by position or keyword, or by keyword.
An advanced function definition may look like the one below:
If you're interested, check out special parameters python docs for more information.
What if you don't know how many arguments you want to be passed into your function?
Python provides us with a solution:
- Arbitrary Arguments - args
- *Arbitrary Keyword Arguments - **kwargs
Arbitrary Arguments, *args
To specify the argument as an arbitrary argument, you need to just add a *(asterisk) before the parameter name in the function definition. The function, in turn, will receive the arguments and save it as a tuple of arguments, and you can access the items accordingly:
Arbitrary Keyword Arguments, **kwargs
Similarly, to specify the argument as an arbitrary keyword argument, you need to add two asterisks: ** before the parameter name in the function definition. The function, in turn, will receive the arguments and save it as a dictionary of arguments, and you can access the items accordingly:
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Also published at https://dev.to/aswin2001barath/functional-programming-in-python-23ff
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