Fix exception when Python is run with -OO (#268)

* Don't assume __doc__ is present

* use correct method

Author: willmcgugan

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [2.4.2] - 2019-02-22
+
+### Fixed
+
+- Fixed exception when Python runs with -OO
+
 ## [2.4.1] - 2019-02-20
 
 ### Fixed

fs/_version.py

@@ -1,3 +1,3 @@
 """Version, used in module and setup.py.
 """
-__version__ = "2.4.1"
+__version__ = "2.4.2"

fs/base.py

@@ -77,13 +77,15 @@ def _method(*args, **kwargs):
         )
         return method(*args, **kwargs)
 
-    _method.__doc__ += """
+    deprecated_msg = """
         Note:
             .. deprecated:: 2.2.0
                 Please use `~{}`
 """.format(
         method.__name__
     )
+    if getattr(_method, "__doc__"):
+        _method.__doc__ += deprecated_msg
 
     return _method