Correctly match package/module names in import hook

tests/test_importhook.py

@@ -6,7 +6,7 @@
 
 import pytest
 
-from typeguard.importhook import install_import_hook
+from typeguard.importhook import TypeguardFinder, install_import_hook
 
 this_dir = Path(__file__).parent
 dummy_module_path = this_dir / 'dummymodule.py'
@@ -99,3 +99,20 @@ def test_inner_class_classmethod(dummymodule):
 def test_inner_class_staticmethod(dummymodule):
     retval = dummymodule.Outer.create_inner_staticmethod()
     assert retval.__class__.__qualname__ == 'Outer.Inner'
+
+
+def test_package_name_matching():
+    """
+    The path finder only matches configured (sub)packages.
+    """
+    packages = ["ham", "spam.eggs"]
+    dummy_original_pathfinder = None
+    finder = TypeguardFinder(packages, dummy_original_pathfinder)
+
+    assert finder.should_instrument("ham")
+    assert finder.should_instrument("ham.eggs")
+    assert finder.should_instrument("spam.eggs")
+
+    assert not finder.should_instrument("spam")
+    assert not finder.should_instrument("ha")
+    assert not finder.should_instrument("spam_eggs")

typeguard/importhook.py

@@ -1,5 +1,4 @@
 import ast
-import re
 import sys
 from importlib.machinery import SourceFileLoader
 from importlib.abc import MetaPathFinder
@@ -94,7 +93,7 @@ class TypeguardFinder(MetaPathFinder):
     """
 
     def __init__(self, packages, original_pathfinder):
-        self._package_exprs = [re.compile(r'^%s\.?' % pkg) for pkg in packages]
+        self.packages = packages
         self._original_pathfinder = original_pathfinder
 
     def find_spec(self, fullname, path=None, target=None):
@@ -113,8 +112,8 @@ def should_instrument(self, module_name: str) -> bool:
         :param module_name: full name of the module that is about to be imported (e.g. ``xyz.abc``)
 
         """
-        for expr in self._package_exprs:
-            if expr.match(module_name):
+        for package in self.packages:
+            if module_name == package or module_name.startswith(package + '.'):
                 return True
 
         return False