path_valid.py

import os


valid_path = "/usr/local/bin:/usr/bin"
invalid_path = "/usr/local/bin::/usr/bin"
invalid_path2 = "/usr/local/bin:.:/usr/bin"


class InvalidPath(Exception):
    def __init__(self, path, entry, position, char_position):
        self.path = path
        self.entry = entry
        self.position = position
        self.char_position = char_position

    def as_string(self, indent_offset=0):
        prefix = 'Invalid path entry `%s` at char %d: ' % (self.entry, self.char_position)
        indent = ' ' * (1 + len(prefix) + self.char_position + indent_offset)
        return prefix + '%s\n%s^' % (self.path, indent)

    def __str__(self):
        return self.as_string()


def validate_path(path):
    location = 0
    for position, entry in enumerate(path.split(':')):
        if not entry or not os.path.isabs(entry):
            raise InvalidPath(path, entry, position, location)
        location += len(entry)


validate_path(valid_path)
try:
    validate_path(invalid_path)
except InvalidPath as exc:
    print("ERROR: " + exc.as_string(indent_offset=7))
try:
    validate_path(invalid_path2)
except InvalidPath as exc:
    print("ERROR: " + exc.as_string(indent_offset=7))