updated dictionary names

[caaker]

Using ch is more consistent with the variable name the comprehension already uses internally, which is ch. Also adds more meaning and description, which is the purpose of a name. The purpose is generally not to identify a type as this can be inferred from the language and code itself.

[Dimey]

there's no distinct character type in python, a character is simply a string of length one – the names are fine, imo