Invoking a function

Even though invoking functions in Python is not about casting a spell or the like, it does sometimes work wonders. Let's start with the concept. Basically, a function is a structured fragment of code we may want to use in more than one place and more than one time. For another thing, functions allow us to read both our code and that of someone else way better. Haven't they become your favorite yet?

Here is a simple function call:

multiply(1, 7)

Here multiply is the name of the function, and numbers in parentheses (1, 7) are its arguments. What is an argument? Well, it's just a value, that will be used inside the body of the function. Let's go deeper into it!

Invoking print()

To call, or invoke, a function in your program, simply write its name and add parentheses after it. That's all it takes! Fun fact: if you've ever typed an expression like this print("Hello, world!"), you already know a little about functions. In this tiny example, however, we see the message "Hello, world!" in the parentheses after the name of the print function. What does it mean? This string is just an argument. And more often than not, functions do have arguments. As for the print function, we may as well use it with no argument at all or even with multiple arguments:

print("Hello, world!")
print()
print("Bye,", "then!")

And here is the output:

Hello, world!

Bye, then!

So, the first call prints one string, the second call of print without arguments prints, in fact, an empty line, and the last call outputs our two messages as one expression. Are you surprised by these results? Then you may learn how the print function works in more detail from its documentation. The Python documentation contains all sorts of information about the function of your interest, for example, which arguments it expects.

Built-in functions

Functions can make life easier, provided one is aware of their existence. Many algorithms are already written, so there is no need for reinvention, except perhaps for educational purposes. The Python interpreter has a number of functions and types built into it, so they are always available. Currently, the number of built-in functions amounts to 69 (in the latest version Python 3.8). Some of them are used to convert the object type, for example, str() returns a string, int() returns an integer, float() returns a floating-point number. Others deal with numbers: you can round() them and sum() them, find the minimum min() or the maximum max(). Still others give us information about the object: its type() or length len(). Let's consider them in action!

In the following example, len() counts the number of characters in the string (the same goes for any sequence).

number = "111"

# finding the length of an object
print(len(number))  # 3

Then we declare the variables integer and float_number and write their sum into my_sum. By the way, the sum() function also deals with sequences.

# converting types
integer = int(number)
float_number = float(number)
print(str(float_number))  # "111.0"

# adding and rounding numbers
my_sum = sum((integer, float_number))

The result is a floating-point number, which becomes clear after printing my_sum.

print(my_sum)  # 222.0
print(round(my_sum))  # 222

Furthermore, you can see how to find the minimum and maximum values: the smallest number equals 111 and the largest number 222.0 belongs to floats .

# finding the minimum and the maximum
print(min(integer, float_number))  # 111
print(type(max(integer, float_number, my_sum)))  # <class 'float'>

There is far more to explore, but let's sum it up.

Recap

The beauty of functions is that we can use them without clear insight into their inner structure and how they manage to perform what we need. But if you want to put a function to good use, make sure to check its documentation or try invoking the special function help() with the name of the function in question wrapped in parentheses. It may become necessary if, for example, the function does not return any value, writes processed data to a file or prints the output on the screen.

Let's make a brief summary:

• functions are meant to be reusable, which means we are free to apply it multiple times with different arguments,

• to call a function write its name followed by parentheses and place the arguments within,

• normally, a function has documentation, which sometimes might be of huge help.