todo.py

from lint import Linter

class TODO(Linter):
    scope = 'string'
    selector = 'comment'
    outline = False

    @classmethod
    def can_lint(cls, language):
        return True

    def lint(self):
        lines = self.code.split('\n')
        for i in range(len(lines)):
            if 'TODO' in lines[i]:
                todo = lines[i].index('TODO')
                self.highlight.range(i, todo, 4)
                self.error(i, 'TODO')