Flake8 the code.

After fixing isort it got visible that we did not do this, yet.

setup.py

@@ -139,6 +139,7 @@ def _read_file(filename):
       },
       python_requires='>=3.7',
       install_requires=[
+          'zope.deferredimport',
           'zope.interface',
           "cffi ; platform_python_implementation == 'CPython'",
       ],

src/persistent/_compat.py

@@ -61,7 +61,7 @@ def _c_optimizations_available():
             'persistent.picklecache': cPickleCache,
             'persistent.timestamp': _timestamp,
         }
-    except catch: # pragma: no cover (only Jython doesn't build extensions)
+    except catch:  # pragma: no cover (only Jython doesn't build extensions)
         return {}
 
 
@@ -93,7 +93,7 @@ def _should_attempt_c_optimizations():
     """
     if _c_optimizations_required():
         return True
-    if PYPY: # pragma: no cover
+    if PYPY:  # pragma: no cover
         return False
     return not _c_optimizations_ignored()
 
@@ -157,7 +157,8 @@ def find_impl():
             return py_impl
 
         c_opts = _c_optimizations_available()
-        if not c_opts: # pragma: no cover (only Jython doesn't build extensions)
+        # only Jython doesn't build extensions:
+        if not c_opts:  # pragma: no cover
             return py_impl
 
         __traceback_info__ = c_opts
@@ -189,7 +190,7 @@ def find_impl():
             v = types.FunctionType(
                 v.__code__,
                 new_globals,
-                k, # name
+                k,  # name
                 v.__defaults__,
                 v.__closure__,
             )

src/persistent/_ring_build.py

@@ -53,7 +53,7 @@
 #define cffi_ring_add(ring, elt) ring_add((CPersistentRing*)ring, (CPersistentRing*)elt)
 #define cffi_ring_del(elt) ring_del((CPersistentRing*)elt)
 #define cffi_ring_move_to_head(ring, elt) ring_move_to_head((CPersistentRing*)ring, (CPersistentRing*)elt)
-"""
+"""   # noqa: E501 line too long
 
 ffi.set_source('persistent._ring',
                source,

src/persistent/dict.py

@@ -11,6 +11,13 @@
 # FOR A PARTICULAR PURPOSE.
 #
 ##############################################################################
+from zope.deferredimport import deprecated
 
-# persistent.dict is deprecated. Use persistent.mapping
-from persistent.mapping import PersistentMapping as PersistentDict
+
+deprecated(
+    "`persistent.dict.PersistentDict` is deprecated. Use"
+    " `persistent.mapping.PersistentMapping` instead."
+    " This backward compatibility shim will be removed in persistent"
+    " version 6.",
+    PersistentDict='persistent.mapping:PersistentMapping',
+)

src/persistent/interfaces.py

@@ -32,6 +32,7 @@
 
 OID_TYPE = SERIAL_TYPE = bytes
 
+
 class IPersistent(Interface):
     """Python persistent interface
 
@@ -356,6 +357,7 @@ def _p_delattr(name):
 
 # TODO:  document conflict resolution.
 
+
 class IPersistentDataManager(Interface):
     """Provide services for managing persistent state.
 
@@ -399,13 +401,13 @@ def register(object):
         """
 
 # Maybe later:
-##     def mtime(object):
-##         """Return the modification time of the object.
+# def mtime(object):
+# """Return the modification time of the object.
 
-##         The modification time may not be known, in which case None
-##         is returned.  If non-None, the return value is the kind of
-##         timestamp supplied by Python's time.time().
-##         """
+# The modification time may not be known, in which case None
+# is returned.  If non-None, the return value is the kind of
+# timestamp supplied by Python's time.time().
+# """
 
 
 class IPickleCache(Interface):
@@ -510,7 +512,6 @@ def new_ghost(oid, obj):
         If 'oid' is already in the cache, raise.
         """
 
-
     def invalidate(to_invalidate):
         """ Invalidate the indicated objects.
 
@@ -537,10 +538,10 @@ def update_object_size_estimation(oid, new_size):
 
     cache_size = Attribute('Target size of the cache')
     cache_drain_resistance = Attribute('Factor for draining cache below '
-                                        'target size')
+                                       'target size')
     cache_non_ghost_count = Attribute('Number of non-ghosts in the cache '
-                                        '(XXX how is it different from '
-                                        'ringlen?')
+                                      '(XXX how is it different from '
+                                      'ringlen?')
     cache_data = Attribute("Property:  copy of our 'data' dict")
     cache_klass_count = Attribute("Property: len of 'persistent_classes'")
 

src/persistent/list.py

@@ -30,9 +30,9 @@ class PersistentList(UserList, persistent.Persistent):
     as changed and automatically persisted.
 
     .. versionchanged:: 4.5.2
-       Using the `clear` method, or deleting a slice (e.g., ``del inst[:]`` or ``del inst[x:x]``)
-       now only results in marking the instance as changed if it actually removed
-       items.
+       Using the `clear` method, or deleting a slice (e.g., ``del inst[:]`` or
+       ``del inst[x:x]``) now only results in marking the instance as changed
+       if it actually removed items.
     """
     __super_getitem = UserList.__getitem__
     __super_setitem = UserList.__setitem__
@@ -67,7 +67,8 @@ def __getitem__(self, item):
 
     if sys.version_info[:3] < (3, 7, 4):  # pragma: no cover
         # Likewise for __copy__.
-        # See https://github.com/python/cpython/commit/3645d29a1dc2102fdb0f5f0c0129ff2295bcd768
+        # See
+        # https://github.com/python/cpython/commit/3645d29a1dc2102fdb0f5f0c0129ff2295bcd768
         def __copy__(self):
             inst = self.__class__.__new__(self.__class__)
             inst.__dict__.update(self.__dict__)

src/persistent/mapping.py

@@ -54,13 +54,13 @@ class PersistentMapping(IterableUserDict, persistent.Persistent):
     __super_pop = IterableUserDict.pop
     __super_popitem = IterableUserDict.popitem
 
-
-    # Be sure to make a deep copy of our ``data`` (See PersistentList.)
-    # See https://github.com/python/cpython/commit/3645d29a1dc2102fdb0f5f0c0129ff2295bcd768
+    # Be sure to make a deep copy of our ``data`` (See PersistentList.) See
+    # https://github.com/python/cpython/commit/3645d29a1dc2102fdb0f5f0c0129ff2295bcd768
     # This was fixed in CPython 3.7.4, but we can't rely on that because it
-    # doesn't handle our old ``_container`` appropriately (it goes directly
-    # to ``self.__dict__``, bypassing the descriptor). The code here was initially
+    # doesn't handle our old ``_container`` appropriately (it goes directly to
+    # ``self.__dict__``, bypassing the descriptor). The code here was initially
     # based on the version found in 3.7.4.
+
     def __copy__(self):
         inst = self.__class__.__new__(self.__class__)
         inst.__dict__.update(self.__dict__)
@@ -141,7 +141,7 @@ def popitem(self):
     # ``data`` when we have ``_container`` instead
 
     @default
-    def data(self): # pylint:disable=method-hidden
+    def data(self):  # pylint:disable=method-hidden
         # We don't want to cause a write on read, so we're careful not to
         # do anything that would cause us to become marked as changed, however,
         # if we're modified, then the saved record will have data, not