Validate type of argument parsed by argparse

argparse_pathtype.py

""" 
    # Usage: 
    
    import argparse
    from argparse_pathtype import PathType
    
    parser = argparse.ArgumentParser(description='Process some integers.')
    parser.add_argument('--dir-models', required=True, type=PathType(path_to="dir"),
                        help='Directory where models are stored')
"""


from argparse import ArgumentTypeError
import pathlib


class PathType:
    def __init__(self, path_to: str = 'file'):
        """
           path_to: file, dir, symlink, None, or a function returning True for valid paths
                None: don't care
        """

        assert path_to in ('file', 'dir', 'symlink', None) or hasattr(path_to, '__call__')
        self._type = path_to

    def __call__(self, string: str):
        resolved_path = pathlib.Path(string).resolve()

        if not resolved_path.exists():
            raise ArgumentTypeError(f"path does not exist: '{string}', '{resolved_path}'")

        if self._type is None:
            pass

        elif self._type == 'file' and not resolved_path.is_file():
            raise ArgumentTypeError(f"path is not a file: '{string}', '{resolved_path}'")

        elif self._type == 'symlink' and not resolved_path.is_symlink():
            raise ArgumentTypeError(f"path is not a symlink: '{string}', '{resolved_path}'")

        elif self._type == 'dir' and not resolved_path.is_dir():
            raise ArgumentTypeError(f"path is not a directory: '{string}', '{resolved_path}'")

        return resolved_path