Why does Pylint object to single-character variable names?

Nowadays there is also an option to override regexp. I.e., if you want to allow single characters as variables:

pylint --variable-rgx="[a-z0-9_]{1,30}$" <filename>

So, Pylint will match PEP8 and will not bring additional violations on top. Also you can add it to .pylintrc.

Pylint checks not only PEP8 recommendations. It has also its own recommendations, one of which is that a variable name should be descriptive and not too short.

You can use this to avoid such short names:

my_list.extend(x_values)

Or tweak Pylint's configuration to tell Pylint what variable name are good.

In strongly typed languages, one-letter name variables can be ok-ish, because you generally get the type next to the name in the declaration of the variable or in the function / method prototype:

bool check_modality(string a, Mode b, OptionList c) {
    ModalityChecker v = build_checker(a, b);
    return v.check_option(c);
}

In Python, you don't get this information, so if you write:

def check_modality(a, b, c):
    v = build_checker(a, b)
    return v.check_option(c)

you're leaving absolutely no clue for the maintenance team as to what the function could be doing, and how it is called, and what it returns. So in Python, you tend to use descriptive names:

def check_modality(name, mode, option_list):
    checker = build_checker(name, mode)
    return checker.check_option(option_list)

And you even add a docstring explaining what the stuff does and what types are expected.

A little more detail on what gurney alex noted: you can tell Pylint to make exceptions for variable names which (you pinky swear) are perfectly clear even though less than three characters. Find in or add to your pylintrc file, under the [FORMAT] header:

# Good variable names which should always be accepted, separated by a comma
good-names=i,j,k,ex,Run,_,pk,x,y

Here pk (for the primary key), x, and y are variable names I've added.