Code indentation

As programmers, when we read code we look at how it's indented to tell us how the code blocks are nested. However, most other programming languages use actual symbols to tell the language parser where a block begins and ends. In coding, the same information in two different places is a violation of the basic best practices of any programming language. So, Python omits the beginning and ending block markers and uses indentation (as shown in the following code screenshot) to inform the parser as well as the programmer:

There is one problem that arises from that, though!

There are different ways of encoding indentation in a text file. These are as follows:

• Use Space characters
• Tab characters
• A combination of both

The codes we're looking at in the preceding code image mixes spaces and tabs, which, in Python 2 was valid, but a terrible idea, and which, in Python 3, is a syntax error. I've configured the editor to highlight tab characters in color, so we can easily see which indentation comes from spaces and which comes from tabs, to see why mixing spaces and tabs is not good, even when it's allowed.

All we have to do is change the tab width and it will look something like the following code image:

Even though the indentation looked good in the previous code image, now it's clearly wrong. There's no ambiguity if all indentation comes from tab characters. So, using only tabs is valid, even in Python 3. However, it is the recommendation of PEP 8 and the Python community that we always use exactly four spaces to indicate one level of indentation. Any halfway decent editor can insert those spaces for us when we press the Tab key. There are several more recommendations, which we're going to go through quickly in the next sub-section.