Python Print() Function: How it works

One of the ubiquitous and most often used functions in python is the python print function. We use it for realizing the output of our codes and even for debugging. So, it is pertinent that we understand how it works.

 

In its essential form what the python print function does is to take a given object, convert it to a string object and print the value out to the standard output, or what is called the screen. It can even send the output to a file.

The python print syntax

The python print function despite its wide ranging value has a simple syntax. The syntax of the python print statement is print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False). I will be explaining each of the arguments in this post. So, just take note of the syntax.

Usually when you want to print something to the screen you provide the python print function with an object or several object arguments. If you don’t specify other parameters, what the function does is print each of the arguments to the screen, each separated by empty space and after all the arguments are printed, to go to a new line. Let’s illustrate this with an example and explain how it relates to the syntax.

When you run the code above, you will see that it nicely prints out each of the objects to the python print function. Here is what happened. I passed it 5 objects and it prints out the five objects each separated by a space. The separation by a space comes about from the sep parameter in the syntax above. The sep means separator. By default its value is a space. Notice that I cast one of the objects to a string before printing it out. This is a trick to make the period adhere to the value of the string. Very cool. We can change the value of the separator. I will highlight it in the separator section below.

Now what happens if we print without passing an object. Let me give an example following from our example above.

You can see that I repeated the earlier code. But on line five I wrote a print statement without giving it any argument or object. If you look at the output on the screen, you will see that it translated it into an empty space. Yes, without any argument the python print function just looks at what is at the end parameter and since the default is a newline, ‘\n’, it creates a new line.

Now let’s see how we can customize the working of the python print function using the keyword parameters outlined in the syntax.

Customizing python print with the sep keyword

The sep keyword separates each of the objects in the python print function based on its value. The default is a whitespace character. That means if you use the default, as outlined above, each of the objects when printed out will be separated by a whitespace.

What if we want another separator on python print, like we want a colon, :, to separate each of the objects to be printed. Here is code that could do it.

If you watch the output to the screen, you could see that each of the objects that was passed to the python print function now has a colon separator between them.

You could create any separator of your imagination. Most times when I have specific ways to print an output it could call for my customizing the separator.

Customizing python print with the end keyword.

The end keyword is another parameter that we could use to customize the python print function. As I highlighted above where I printed a print function without objects, the default for the end keyword is a newline, ‘\n’, which creates a new line after printing the objects. That means python print adds a newline to each line. Most times when I want python print without newlines, that means, subsequent lines of objects to print on the same line, I customize the end keyword. You just replace the default with a space character, ‘ ‘, which signifies to concatenate all the subsequent lines on one single line.

For example, you have code you want printed in the same line. Here is the code that could do it.

You can see that by customizing the end parameter to a space, I have made all the objects in the python print function print without newline to the same line.

How to print to file using file keyword

Most usually when you call the python print function, it prints to standard output, that is, the screen. That is the default. I will show you how to print to a file. You can customize it to print to a file by specifying a file object as the value to the file parameter which file object should be writable. For details on how to open, read, and make files writable, see this blog post.

Now, let’s take an example. This time instead of printing to the screen we will be printing to a file or writing to a file. Here is the code:

    
text = 'I feel cool using python.
        \nIt is the best programming language'
with open('new_file.txt', 'w') as source_file:
    print(text, file=source_file)

You can run it on your machine. When you do, rather than getting the text message to your screen, it will print to the file, new_file.txt. If new_file.txt doesn’t exist, it will create one.

One thing to note about file objects passed to the file keyword – you cannot use binary mode file objects. This is because python print function converts all its objects to the str class (strings) before passing them to the file. So, note this and if you want to write to binary mode file objects, use the write methods that are built-in for file objects.

You must really be feeling empowered with all the cool features in python print function. I am. You can subscribe to my blog or leave a comment below. I feel happy when I believe I have made an impact.

Happy pythoning.