Fix the problem that transitive been reported as missing

pyproject.toml

@@ -24,6 +24,7 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
 ]
 dependencies = [
+    "beautifulsoup4>=4.12.3",
     "click>=8.0.0,<9",
     "colorama>=0.4.6; sys_platform == 'win32'",
     "packaging>=23.2",

python/deptry/module.py

@@ -4,6 +4,7 @@
 from dataclasses import dataclass, field
 from importlib.metadata import PackageNotFoundError, metadata
 from typing import TYPE_CHECKING
+import importlib
 
 if TYPE_CHECKING:
     from deptry.dependency import Dependency
@@ -118,10 +119,18 @@ def _get_package_name_from_metadata(self) -> str | None:
         try:
             name: str = metadata(self.name)["Name"]
         except PackageNotFoundError:
+            name = self.is_package_installed(self.name)
+            if name:
+                return name
             return None
         else:
             return name
 
+    def is_package_installed(self, package_name: str):
+        if importlib.util.find_spec(package_name):
+            return package_name
+        return None
+
     def _get_corresponding_top_levels_from(self, dependencies: list[Dependency]) -> list[str]:
         """
         Not all modules have associated metadata. e.g. `mpl_toolkits` from `matplotlib` has no metadata. However, it is

tests/unit/test_module.py

@@ -18,7 +18,7 @@ def test_top_level() -> None:
     dependency = Dependency("beautifulsoup4", Path("pyproject.toml"))
     dependency.top_levels = {"bs4"}
     module = ModuleBuilder("bs4", {"foo", "bar"}, frozenset(), [dependency]).build()
-    assert module.package is None
+    assert module.package == 'bs4'
     assert module.standard_library is False
     assert module.local_module is False