Functions in Python are the defined blocks of code that perform a specific task. In this section, we will discuss the difference in invoking functions with and without Parentheses.
- When we call a function with parentheses, the function gets execute and returns the result to the callable.
- In another case, when we call a function without parentheses, a function reference is sent to the callable rather than executing the function itself.
Let’s discuss 3 important concepts:
- Invoking functions
- Return functions
- Passing functions
Invoking functions –
The below function performs a simple task, string concatenation. Here we will invoke the function `concatenate_string` with and without parentheses and see the difference.
def concatenate_string(*args): string1 = args[0] string2 = args[1] return string1 + string2 obj = concatenate_string('Hello, ', 'George')print('Function call with Parentheses: ')print(obj) obj = concatenate_stringprint('Function call without Parentheses: ')print(obj) |
Output
Function call with Parentheses: Hello, George Function call without Parentheses: <function concatenate_string at 0x7f0bb991df28>
For the first case, when we call concatenate_string('Hello, ', 'George'), the function executes and returns the concatenated string.
And, for the second case, when we call concatenate_string i.e. without parentheses, a reference is passed to the callable rather than executing the function itself. Here the callable can decide what to do with the reference.
Return Functions –
From the above discussion you can understand that, when the function is called with parentheses, the code is executed and returns the result. And, when it is called without parentheses, a function reference is returned to the callable.
So, what happens when a function is coded along with a return statement with parentheses and without parentheses. Let’s go through an example.
With Parentheses
def concatenate_string(*args): string1 = args[0] string2 = args[1] def merge_string(string1, string2): return string1 + string2 return merge_string(string1, string2) def func(): conc_obj = concatenate_string('Hello, ', 'George') print(conc_obj) func() |
Output
Hello, George
From the above example, it’s clear that the merge_string is a function within the function concatenate_string and the main function (concatenate_string) returns the sub-function (merge_string) to the caller.
return merge_string(string1, string2) Here merge_string is invoked with parentheses, hence it executes and provides the result to the concatenate_string from where the result is passed to func.
Without Parentheses
def concatenate_string(): def merge_string(string1, string2): return string1 + string2 return merge_string def func(): # return the reference of merge_string func conc_obj = concatenate_string() print(conc_obj) # prints the reference # executes the reference print(conc_obj('Hello, ', 'George')) func() |
Output:
<function concatenate_string..merge_string at 0x7f1e54ebc158> Hello, George
Since the merge_string is used without parentheses, the concatenate_string passes the function reference to the callable func rather than executing the merge_string.
return merge_stringHence, we can conclude that when we code sub-function with parentheses in a return statement, the main function executes the sub-function and passes the result to the callable.
And, when we code subfunction without parentheses in a return statement, the main function passes the sub-function reference to the callable rather than executing it. Here the callable decides what to do with the reference.
Passing Functions –
You can pass a function as an argument by creating the reference, calling the function without parentheses, and provide it as an argument. Let’s look into the code.
def concatenate_string(*args): string1 = args[0] string2 = args[1] def merge_string(string1, string2): return string1 + string2 # string merge # executes merge_string and return the result return merge_string(string1, string2) def function_call(function): string1 = 'Hello, ' string2 = 'George' return function(string1, string2) # passing function as argumentprint(function_call(concatenate_string)) |
Output:
Hello, George
In this case, the reference of concatenate_string is passed to the function_call as an argument.
function_call(concatenate_string)Inside function_call, it executes the concatenate_string using the reference and returns the result to the callable.
