core[patch]: utils.guard_import fix (#21133)

Issues (nit): 
1. `utils.guard_import` prints wrong error message when there is an
import `error.` It prints the whole `module_name` but should be only the
first part as the pip package name. E.i. `langchain_core.utils` -> print
not `langchain-core` but `langchain_core.utils`. Also replace '_' with
'-' in the pip package name.
2. it does not handle the `ModuleNotFoundError` which raised if
`guard_import("wrong_module")`

Fixed issues; added ut-s. Controversial: I've reraised
`ModuleNotFoundError` as `ImportError`, since in case of the error, the
proposed action is the same - we need to install a missed package.

libs/core/langchain_core/utils/utils.py

@@ -1,4 +1,5 @@
 """Generic utility functions."""
+
 import contextlib
 import datetime
 import functools
@@ -88,10 +89,11 @@ def guard_import(
     installed."""
     try:
         module = importlib.import_module(module_name, package)
-    except ImportError:
+    except (ImportError, ModuleNotFoundError):
+        pip_name = pip_name or module_name.split(".")[0].replace("_", "-")
         raise ImportError(
             f"Could not import {module_name} python package. "
-            f"Please install it with `pip install {pip_name or module_name}`."
+            f"Please install it with `pip install {pip_name}`."
         )
     return module
 

libs/core/tests/unit_tests/utils/test_utils.py

@@ -1,11 +1,12 @@
 import re
 from contextlib import AbstractContextManager, nullcontext
-from typing import Dict, Optional, Tuple, Type, Union
+from typing import Any, Dict, Optional, Tuple, Type, Union
 from unittest.mock import patch
 
 import pytest
 
-from langchain_core.utils import check_package_version
+from langchain_core import utils
+from langchain_core.utils import check_package_version, guard_import
 from langchain_core.utils._merge import merge_dicts
 
 
@@ -113,3 +114,60 @@ def test_merge_dicts(
     with err:
         actual = merge_dicts(left, right)
         assert actual == expected
+
+
+@pytest.mark.parametrize(
+    ("module_name", "pip_name", "package", "expected"),
+    [
+        ("langchain_core.utils", None, None, utils),
+        ("langchain_core.utils", "langchain-core", None, utils),
+        ("langchain_core.utils", None, "langchain-core", utils),
+        ("langchain_core.utils", "langchain-core", "langchain-core", utils),
+    ],
+)
+def test_guard_import(
+    module_name: str, pip_name: Optional[str], package: Optional[str], expected: Any
+) -> None:
+    if package is None and pip_name is None:
+        ret = guard_import(module_name)
+    elif package is None and pip_name is not None:
+        ret = guard_import(module_name, pip_name=pip_name)
+    elif package is not None and pip_name is None:
+        ret = guard_import(module_name, package=package)
+    elif package is not None and pip_name is not None:
+        ret = guard_import(module_name, pip_name=pip_name, package=package)
+    else:
+        raise ValueError("Invalid test case")
+    assert ret == expected
+
+
+@pytest.mark.parametrize(
+    ("module_name", "pip_name", "package"),
+    [
+        ("langchain_core.utilsW", None, None),
+        ("langchain_core.utilsW", "langchain-core-2", None),
+        ("langchain_core.utilsW", None, "langchain-coreWX"),
+        ("langchain_core.utilsW", "langchain-core-2", "langchain-coreWX"),
+        ("langchain_coreW", None, None),  # ModuleNotFoundError
+    ],
+)
+def test_guard_import_failure(
+    module_name: str, pip_name: Optional[str], package: Optional[str]
+) -> None:
+    with pytest.raises(ImportError) as exc_info:
+        if package is None and pip_name is None:
+            guard_import(module_name)
+        elif package is None and pip_name is not None:
+            guard_import(module_name, pip_name=pip_name)
+        elif package is not None and pip_name is None:
+            guard_import(module_name, package=package)
+        elif package is not None and pip_name is not None:
+            guard_import(module_name, pip_name=pip_name, package=package)
+        else:
+            raise ValueError("Invalid test case")
+    pip_name = pip_name or module_name.split(".")[0].replace("_", "-")
+    err_msg = (
+        f"Could not import {module_name} python package. "
+        f"Please install it with `pip install {pip_name}`."
+    )
+    assert exc_info.value.msg == err_msg