Reading programs

In order to help you follow the programs, we have adopted two different type fonts – a variable-width font (where letters have different widths, such as the bulk of the text here) and a mono-spaced font, such as the Courier font found on old mechanical typewriters that looks like this.

The reason for using a mono-spaced font to represent code is twofold. First, it tells the reader that a word is computer code and not just part of the narrative text. Second, spacing in computer programs is important for readability, and mono-spaced fonts line up letters and numbers on adjacent rows neatly in columns. The following is an example of code from a later chapter to demonstrate this point. The proportionally-spaced text to the right, prefixed by #, indicates that the text is not code but a plain-language comment:

elif litV[0]   == '%': literal = int(litV[1:],2)     # If first % convert binary to integer
elif litV...