Fix flake8 issues

Signed-off-by: Stefano Bennati <stefano.bennati@here.com>

src/resolvelib/resolvers.py

@@ -283,10 +283,10 @@ def _backjump(self, causes):
 
         Each iteration of the loop will:
 
-        1.  Identify Z. The incompatibility is not necessarily caused by the latest state.
+        1.  Identify Z. The incompatibility is not always caused by the latest state.
             For example, given three requirements A, B and C, with dependencies
-            A1, B1 and C1, where A1 and B1 are incompatible:
-            the last state might be related to C, so we want to discard the previous state.
+            A1, B1 and C1, where A1 and B1 are incompatible: the last state
+            might be related to C, so we want to discard the previous state.
         2.  Discard Z.
         3.  Discard Y but remember its incompatibility information gathered
             previously, and the failure we're dealing with right now.
@@ -310,9 +310,10 @@ def _backjump(self, causes):
                 # Retrieve the last candidate pin and known incompatibilities.
                 try:
                     broken_state = self._states.pop()
-                except:
+                except IndexError:
                     raise Exception(
-                        "Exhausted all states during backjumping, impossible to find a fully-compatible dependency tree."
+                        "Exhausted all states during backjumping, "
+                        "impossible to find a fully-compatible dependency tree."
                     )
                 name, candidate = broken_state.mapping.popitem()
                 current_dependencies = {

tests/test_resolvers.py

@@ -1,15 +1,3 @@
-from typing import (
-    Any,
-    Iterable,
-    Iterator,
-    List,
-    Mapping,
-    Sequence,
-    Set,
-    Tuple,
-    Union,
-)
-
 import pytest
 from packaging.requirements import Requirement
 from packaging.version import Version
@@ -22,8 +10,6 @@
     Resolver,
 )
 from resolvelib.resolvers import (
-    Criterion,
-    RequirementInformation,
     RequirementsConflicted,
     Resolution,
 )
@@ -171,9 +157,6 @@ def test_pin_conflict_with_self(monkeypatch, reporter):
     Verify correct behavior of attempting to pin a candidate version that conflicts
     with a previously pinned (now invalidated) version for that same candidate (#91).
     """
-    Candidate = Tuple[
-        str, Version, Sequence[str]
-    ]  # name, version, requirements
     all_candidates = {
         "parent": [("parent", Version("1"), ["child<2"])],
         "child": [