Fixed conditional import x.y causing possibly-used-before-assignment (#10240) (#10241)

(cherry picked from commit 7b28cf4)

Co-authored-by: Alex Prabhat Bara <alexpbara@gmail.com>

Author: jacobtylerwalls

doc/whatsnew/fragments/10081.bugfix

@@ -0,0 +1,3 @@
+Fixed conditional import x.y causing false positive possibly-used-before-assignment.
+
+Closes #10081

pylint/checkers/variables.py

@@ -967,7 +967,9 @@ def _defines_name_raises_or_returns(name: str, node: nodes.NodeNG) -> bool:
             ):
                 return True
         if isinstance(node, (nodes.Import, nodes.ImportFrom)) and any(
-            (node_name[1] and node_name[1] == name) or (node_name[0] == name)
+            (node_name[1] and node_name[1] == name)
+            or (node_name[0] == name)
+            or (node_name[0].startswith(name + "."))
             for node_name in node.names
         ):
             return True

tests/functional/u/used/used_before_assignment.py

@@ -222,3 +222,12 @@ def print_platform_specific_command(self):
             self.skip("only runs on Linux/Windows")
 
         print(cmd)
+
+
+def conditional_import():
+    if input():
+        import os.path
+    else:
+        os = None
+    if os:
+        pass