How to use the checklist.RepoValidator function in checklist

def _validate(self, root, dirs, files):
        # If any of the directories yet to be visited should be skipped, remove
        # them from ``dirs`` so that we don't visit them in a future iteration.
        # This guarantees that ``root`` is a valid directory that should not be
        # skipped (since we're doing a top-down walk).
        for skip_dir in self.skip_dirs:
            if skip_dir in dirs:
                dirs.remove(skip_dir)

        invalid_dirs = []
        if '__init__.py' not in files:
            invalid_dirs.append(root)
        return invalid_dirs


class ExecPermissionValidator(RepoValidator):
    """Flag code files that have execute permissions.

    Parameters
    ----------
    extensions : iterable of str, optional
        File extensions of files to validate. Defaults to Python, Cython, and
        C files (header and source files).

    """
    reason = "Library code with execute permissions:"

    def __init__(self, extensions=None):
        if extensions is None:
            extensions = {'.py', '.pyx', '.h', '.c'}
        self.extensions = set(extensions)

This code was taken from verman's
        ``verman.Version.verman_system_call``. See licenses/verman.txt and
        https://github.com/biocore/verman for more details.

        """
        proc = subprocess.Popen(cmd, shell=True, universal_newlines=True,
                                stdout=subprocess.PIPE, stderr=subprocess.PIPE)

        # communicate pulls all stdout/stderr from the PIPEs to
        # avoid blocking -- don't remove this line!
        stdout, stderr = proc.communicate()
        return_value = proc.returncode
        return stdout, stderr, return_value


class CopyrightHeadersValidator(RepoValidator):
    """Flag library files with non-standard copyright headers

    See the current standard for scikit-bio's copyright headers at
    ``http://scikit-bio.org/docs/latest/development/new_module.html``

    Individual files are ignored if the first line in the file is exactly:

    # checklist.py:CopyrightHeadersValidator IGNORE

    If a file is ignored, a ``ChecklistWarning`` is raised.

    Parameters
    ----------
    skip_dirs : iterable of str, optional
        Directory names to skip during validation. Defaults to skipping any
        directories named ``'data'`` or ``'__pycache__'`` (and anything

if tokens[pos][0] == tokenize.STRING:
                pos += 3
            # copyright header consists of 7 lines, and by discussion in
            # preceding comment, spans through 14 tokens.
            cheader = ''.join(map(lambda x: x[1], tokens[pos:pos + 14]))
            # Ensure that there is no blank line at the end of the file
            if (cheader != self.COPYRIGHT_HEADER or
                    (tokens[pos + 14][0] != tokenize.NL and
                     tokens[pos + 14][0] != tokenize.ENDMARKER)):
                invalid_files.append(f.name)
            f.close()

        return invalid_files


class InitValidator(RepoValidator):
    """Flag library code directories that are missing init files.

    This type of validation is important mainly because it is very easy to
    forget to add an __init__.py file to a new test directory. If this
    happens, nose will skip those tests unless it is run from the root of the
    source repository. Thus, the tests will be skipped if the package is
    pip-installed, e.g., as an end-user might install a release.

    Parameters
    ----------
    skip_dirs : iterable of str, optional
        Directory names to skip during validation. Defaults to skipping any
        directories named ``'data'`` or ``'__pycache__'`` (and anything
        contained within them).

    """

Returns
        -------
        list of str
            List of filepaths or dirpaths to be considered invalid (i.e., that
            did not pass the validation checks).

        See Also
        --------
        os.walk

        """
        raise NotImplementedError("Subclasses must implement _validate.")


class InitValidator(RepoValidator):
    """Flag library code directories that are missing init files.

    This type of validation is important mainly because it is very easy to
    forget to add an __init__.py file to a new test directory. If this
    happens, nose will skip those tests unless it is run from the root of the
    source repository. Thus, the tests will be skipped if the package is
    pip-installed, e.g., as an end-user might install a release.

    Parameters
    ----------
    skip_dirs : iterable of str, optional
        Directory names to skip during validation. Defaults to skipping any
        directories named ``'data'`` or ``'__pycache__'`` (and anything
        contained within them).

    """

self.extensions = set(extensions)

    def _validate(self, root, dirs, files):
        invalid_fps = []
        for f in files:
            _, ext = os.path.splitext(f)

            if ext in self.extensions:
                fp = os.path.join(root, f)

                if os.access(fp, os.X_OK):
                    invalid_fps.append(fp)
        return invalid_fps


class GeneratedCythonValidator(RepoValidator):
    """Flag Cython files that are missing generated C files.

    Flags Cython files that aren't paired with a generated C file. The
    generated C file must be in the same directory as the Cython file, and its
    name (besides the file extension) must match. The validator also ensures
    that the generated C file is not empty.

    Parameters
    ----------
    cython_ext : str, optional
        File extension for Cython files.
    c_ext : str, optional
        File extension for generated C files.

    """
    reason = "Cython code missing generated C code"

def _validate(self, root, dirs, files):
        # If any of the directories yet to be visited should be skipped, remove
        # them from ``dirs`` so that we don't visit them in a future iteration.
        # This guarantees that ``root`` is a valid directory that should not be
        # skipped (since we're doing a top-down walk).
        for skip_dir in self.skip_dirs:
            if skip_dir in dirs:
                dirs.remove(skip_dir)

        invalid_dirs = []
        if '__init__.py' not in files:
            invalid_dirs.append(root)
        return invalid_dirs


class ExecPermissionValidator(RepoValidator):
    """Flag code files that have execute permissions.

    Parameters
    ----------
    extensions : iterable of str, optional
        File extensions of files to validate. Defaults to Python, Cython, and
        C files (header and source files).

    """
    reason = "Library code with execute permissions"

    def __init__(self, extensions=None):
        if extensions is None:
            extensions = {'.py', '.pyx', '.h', '.c'}
        self.extensions = set(extensions)

if c_ts < cython_ts:
                    invalid_fps.append(cython_fp)

        return invalid_fps

    def _get_timestamp(self, fp):
        cmd = 'git log -1 --format="%%ad" -- %s' % fp
        stdout, stderr, retval = self._system_call(cmd)

        if retval != 0:
            raise RuntimeError("Could not execute 'git log' command to "
                               "determine file timestamp.")
        return dateutil.parser.parse(stdout.strip())


class APIRegressionValidator(RepoValidator):
    """Flag tests that import from a non-minimized subpackage hierarchy.

    Flags tests that aren't imported from a minimally deep API target. (e.g.
    skbio.TabularMSA vs skbio.alignment.TabularMSA). This should prevent
    accidental regression in our API because tests will fail if any alias is
    removed, and this checklist will fail if any test doesn't import from the
    least deep API target.

    """
    reason = ("The following tests import `A` but should import `B`"
              " (file: A => B):")

    def __init__(self):
        self._imports = {}

    def _validate(self, root, dirs, files):

self.extensions = set(extensions)

    def _validate(self, root, dirs, files):
        invalid_fps = []
        for f in files:
            _, ext = os.path.splitext(f)

            if ext in self.extensions:
                fp = os.path.join(root, f)

                if os.access(fp, os.X_OK):
                    invalid_fps.append(fp)
        return invalid_fps


class GeneratedCythonValidator(RepoValidator):
    """Flag Cython files that have missing or outdated generated C files.

    Flags Cython files that aren't paired with an up-to-date generated C file.
    The generated C file must be in the same directory as the Cython file, and
    its name (besides the file extension) must match. The validator also
    ensures that the generated C file is not empty and that it was generated at
    the same time or later than the Cython file's timestamp.

    Parameters
    ----------
    cython_ext : str, optional
        File extension for Cython files.
    c_ext : str, optional
        File extension for generated C files.

    """