{"record":{"id":"77ddf29dac97680b","repo":"PrefectHQ/fastmcp","slug":"failed-to-import-module-name-from-file-path","errorCode":null,"errorMessage":"Failed to import {module_name} from {file_path}: {e}","messagePattern":"Failed to import (.+?) from (.+?): (.+?)","errorType":"exception","errorClass":"ImportError","httpStatus":null,"severity":"error","filePath":"fastmcp_slim/fastmcp/server/providers/filesystem_discovery.py","lineNumber":199,"sourceCode":"        # normally beneath it.\n        top_name = module_name.split(\".\")[0]\n        existing_top = sys.modules.get(top_name)\n        if existing_top is not None and not _package_path_matches(\n            existing_top, package_root\n        ):\n            anchor = _private_package_prefix(package_root.parent)\n            if anchor not in sys.modules:\n                spec = ModuleSpec(anchor, loader=None, is_package=True)\n                anchor_module = importlib.util.module_from_spec(spec)\n                anchor_module.__path__ = [str(package_root.parent)]\n                sys.modules[anchor] = anchor_module\n            private_name = f\"{anchor}.{module_name}\"\n            try:\n                if private_name in sys.modules:\n                    return importlib.reload(sys.modules[private_name])\n                return importlib.import_module(private_name)\n            except ImportError as e:\n                raise ImportError(\n                    f\"Failed to import {module_name} from {file_path}: {e}\"\n                ) from e\n\n        # Temporarily add package root's parent to sys.path for the import\n        package_parent = str(package_root.parent)\n        path_added = package_parent not in sys.path\n        if path_added:\n            sys.path.insert(0, package_parent)\n\n        try:\n            # If already imported, reload to pick up changes (for reload mode)\n            if module_name in sys.modules:\n                return importlib.reload(sys.modules[module_name])\n            return importlib.import_module(module_name)\n        except ImportError as e:\n            raise ImportError(\n                f\"Failed to import {module_name} from {file_path}: {e}\"\n            ) from e","sourceCodeStart":181,"sourceCodeEnd":217,"githubUrl":"https://github.com/PrefectHQ/fastmcp/blob/1f021142978e0861cd910c8df4e8074bc7cf3978/fastmcp_slim/fastmcp/server/providers/filesystem_discovery.py#L181-L217","documentation":"`import_module_from_file` imports a file as a submodule under a private package anchor (e.g. `_fastmcp_tool_xxx`). When `importlib.import_module(private_name)` raises ImportError — typically because a module imported *by* the target file cannot be resolved, or a relative import fails outside a proper package — it is re-raised with this message wrapping the original cause.","triggerScenarios":"Calling `discover_and_import` (or the tests) on a file whose module body does `import some_missing_lib` or uses `from . import x` when the file is not importable as a package; the private anchor package exists but the nested import fails.","commonSituations":"Discovered tool files with undeclared dependencies; files relying on relative imports but loaded outside a real package layout; PYTHONPATH missing a dependency; typos in imports inside hot-reloaded plugin files.","solutions":["Read the chained `__cause__` (`raise ... from e`) to see which inner import failed and install/fix that dependency","Move relative imports (`from . import x`) to absolute imports or ensure the file lives in a real package with `__init__.py`","Verify sys.path contains the directory the plugin file expects (the loader temporarily adds the package parent, but transitive deps may live elsewhere)","Test the file standalone with `python -c \"import your_module\"` to reproduce the import error outside FastMCP"],"exampleFix":"// before\n# plugin.py\nfrom .helpers import build  # fails: not in a real package\n// after\n# plugin.py\nfrom helpers import build  # absolute import, helpers.py next to plugin.py","handlingStrategy":"try-catch","validationCode":"import ast, pathlib\ndef check_imports(path):\n    tree = ast.parse(pathlib.Path(path).read_text())\n    return [n for n in ast.walk(tree) if isinstance(n, ast.ImportFrom) and n.level > 0]","typeGuard":"def is_importable_py_file(p):\n    return p.is_file() and p.suffix == '.py'","tryCatchPattern":"try:\n    mod = provider.import_module_from_file(path)\nexcept ImportError as e:\n    log.error('import failed for %s: cause=%r', path, e.__cause__)","preventionTips":["Use absolute imports in plugin/discovered files","Install all plugin dependencies in the runtime environment","Run `python -m py_compile` or an import smoke test on plugin files before deploying"],"tags":["python","import","module-loading","plugin-discovery"],"backgroundTag":"importerror-module-not-found","analyzedSha":"1f021142978e0861cd910c8df4e8074bc7cf3978","analyzedAt":"2026-08-29T14:31:16.082Z","schemaVersion":2},"datasetVersion":"2026-08-29T17:17:51.833Z"}