Added support for MDTM command in FTPFS.getmodified.

Author: atollk

CHANGELOG.md

@@ -25,6 +25,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   test suites.
 - `FSTestCases` now builds the large data required for `upload` and `download` tests only
   once in order to reduce the total testing time.
+- FTP servers that do not support the MLST command now try to use the MDTM command to
+  retrieve the last modification timestamp of a resource. 
+  Closes [#456](https://github.com/PyFilesystem/pyfilesystem2/pull/456).
 
 ### Fixed
 

fs/base.py

@@ -22,6 +22,7 @@
 import six
 
 from . import copy, errors, fsencode, iotools, move, tools, walk, wildcard
+from .errors import Unsupported
 from .glob import BoundGlobber
 from .mode import validate_open_mode
 from .path import abspath, join, normpath
@@ -675,8 +676,16 @@ def getmodified(self, path):
         The *modified timestamp* of a file is the point in time
         that the file was last changed. Depending on the file system,
         it might only have limited accuracy.
+
         """
-        return self.getinfo(path, ("detail", "modified")).modified
+        timestamp = self.getinfo(path, ("detail", "modified")).modified
+        if timestamp is None:
+            raise Unsupported(
+                "Last modified time is not supported by the filesystem for the requested resource: "
+                + path
+            )
+        else:
+            return timestamp
 
     def getmeta(self, namespace="standard"):
         # type: (Text) -> Mapping[Text, object]

fs/ftpfs.py

@@ -16,6 +16,8 @@
 from datetime import datetime
 from ftplib import FTP
 
+from .time import epoch_to_datetime
+
 try:
     from ftplib import FTP_TLS
 except ImportError as err:
@@ -579,11 +581,14 @@ def create(self, path, wipe=False):
     def getmodified(self, path):
         # type: (Text) -> datetime
         if "MDTM" in self.features:
-            # TODO
-            pass
-
-        return self.getinfo(path, ["details", "modified"]).modified
-
+            with self._lock:
+                with ftp_errors(self, path=path):
+                    cmd = "MDTM " + _encode(self.validatepath(path), self.ftp.encoding)
+                    response = self.ftp.sendcmd(cmd)
+                time_num = self._parse_ftp_time(response.split()[1])
+                if time_num is not None:
+                    return epoch_to_datetime(time_num)
+        return super(FTPFS, self).getmodified(path)
 
     @classmethod
     def _parse_ftp_time(cls, time_text):