There are several rules for naming variables in Python. These are the following:

• a variable name must start with a letter or the underscore character, which means a variable name can not begin with a number.
• a variable name may contain only English letters, numbers, and underscore characters.
• variables names are case sensitive, i.e., Chapter, chapter, and CHAPTER will be considered by Python as three different objects.

Above we considered the 'technical' side of naming variables. At the same time, there are several conventions between programmers on namings. These are:

• variables names should be in lowercase.
• variables names containing several words should have words separated by the underscore characters (_).

These rules are not compulsory but are recommended. For example, if you need to store the number of user's points, it will be much better to use points, num_of_points, or n_points namings instead of n, p, or something like these.