Emit used-before-assignment when reimporting later in a function (#…

…6979)

doc/whatsnew/2/2.15/index.rst

@@ -61,6 +61,10 @@ False negatives fixed
 
   Closes #6812
 
+* Emit ``used-before-assignment`` when relying on a name that is reimported later in a function.
+
+  Closes #4624
+
 * Emit ``used-before-assignment`` for self-referencing assignments under if conditions.
 
   Closes #6643

pylint/checkers/variables.py

@@ -296,12 +296,15 @@ def _fix_dot_imports(not_consumed):
     return sorted(names.items(), key=lambda a: a[1].fromlineno)
 
 
-def _find_frame_imports(name, frame):
+def _find_frame_imports(name: str, frame: nodes.LocalsDictNodeNG) -> bool:
     """Detect imports in the frame, with the required *name*.
 
-    Such imports can be considered assignments.
+    Such imports can be considered assignments if they are not globals.
     Returns True if an import for the given name was found.
     """
+    if name in _flattened_scope_names(frame.nodes_of_class(nodes.Global)):
+        return False
+
     imports = frame.nodes_of_class((nodes.Import, nodes.ImportFrom))
     for import_node in imports:
         for import_name, import_alias in import_node.names:
@@ -312,10 +315,10 @@ def _find_frame_imports(name, frame):
                     return True
             elif import_name and import_name == name:
                 return True
-    return None
+    return False
 
 
-def _import_name_is_global(stmt, global_names):
+def _import_name_is_global(stmt, global_names) -> bool:
     for import_name, import_alias in stmt.names:
         # If the import uses an alias, check only that.
         # Otherwise, check only the import name.
@@ -334,10 +337,13 @@ def _flattened_scope_names(
     return set(itertools.chain.from_iterable(values))
 
 
-def _assigned_locally(name_node):
+def _assigned_locally(name_node: nodes.Name):
     """Checks if name_node has corresponding assign statement in same scope."""
-    assign_stmts = name_node.scope().nodes_of_class(nodes.AssignName)
-    return any(a.name == name_node.name for a in assign_stmts)
+    name_node_scope = name_node.scope()
+    assign_stmts = name_node_scope.nodes_of_class(nodes.AssignName)
+    return any(a.name == name_node.name for a in assign_stmts) or _find_frame_imports(
+        name_node.name, name_node_scope
+    )
 
 
 def _has_locals_call_after_node(stmt, scope):

tests/functional/u/used/used_before_assignment.py

@@ -1,4 +1,4 @@
-"""pylint doesn't see the NameError in this module"""
+"""Miscellaneous used-before-assignment cases"""
 # pylint: disable=consider-using-f-string, missing-function-docstring
 __revision__ = None
 
@@ -13,3 +13,16 @@ def inner():
         pass
 
 outer()
+
+
+# pylint: disable=unused-import, wrong-import-position, import-outside-toplevel, reimported, redefined-outer-name, global-statement
+import time
+def redefine_time_import():
+    print(time.time())  # [used-before-assignment]
+    import time
+
+
+def redefine_time_import_with_global():
+    global time  # pylint: disable=invalid-name
+    print(time.time())
+    import time

tests/functional/u/used/used_before_assignment.txt

@@ -1,3 +1,4 @@
 used-before-assignment:6:19:6:22::Using variable 'MSG' before assignment:HIGH
 used-before-assignment:8:20:8:24::Using variable 'MSG2' before assignment:HIGH
 used-before-assignment:11:4:11:9:outer:Using variable 'inner' before assignment:HIGH
+used-before-assignment:21:10:21:14:redefine_time_import:Using variable 'time' before assignment:HIGH