Use ModuleNotFoundError instead of ImportError where appropriate.

The new exception was introduced in Python 3.6.

rst/installation.rst

@@ -58,7 +58,7 @@ that is not the case.
   To check if a specific module :var:`<module>` is installed, execute
   :samp:`python3 -c 'import {<module>};
   print({<module>}.__version__)'`. This will result in an
-  `ImportError` if the module is not installed, and will print the
+  `ModuleNotFoundError` if the module is not installed, and will print the
   installed version if the module is installed.
 
 

setup.py

@@ -10,7 +10,7 @@
 
 try:
     import setuptools
-except ImportError:
+except ModuleNotFoundError:
     raise SystemExit('Setuptools package not found. Please install from '
                      'https://pypi.python.org/pypi/setuptools')
 from setuptools import Extension
@@ -54,7 +54,7 @@ def run(self):
         try:
             from sphinx.application import Sphinx
             from docutils.utils import SystemMessage
-        except ImportError:
+        except ModuleNotFoundError:
             raise SystemExit('This command requires Sphinx to be installed.') from None
 
         fix_docutils()

src/s3ql/backends/gs.py

@@ -34,7 +34,7 @@
 
 try:
     import google.auth as g_auth
-except ImportError:
+except ModuleNotFoundError:
     g_auth = None
 
 

src/s3ql/block_cache.py

@@ -25,7 +25,7 @@
 
 try:
     from contextlib import asynccontextmanager
-except ImportError:
+except ModuleNotFoundError:
     from async_generator import asynccontextmanager
 
 # standard logger for this module

src/s3ql/multi_lock.py

@@ -11,7 +11,7 @@
 
 try:
     from contextlib import asynccontextmanager
-except ImportError:
+except ModuleNotFoundError:
     from async_generator import asynccontextmanager
 
 __all__ = [ "MultiLock" ]