Improve performance of jinja2_convenience_function by not importing NAPALM when called (#466)

* Improve performance of jinja2_convenience_function by not importing NAPALM unnecessarily

* Fix optional test as well

Author: glennmatthews

netutils/lib_helpers.py

@@ -5,14 +5,6 @@
 
 from netutils.lib_mapper import NAPALM_LIB_MAPPER
 
-try:
-    from napalm import get_network_driver
-    from napalm.base.exceptions import ModuleImportError
-except ImportError:
-    HAS_NAPALM = False
-else:
-    HAS_NAPALM = True
-
 
 def get_napalm_getters() -> t.Dict[str, t.Dict[str, bool]]:
     """Utility to return a dictionary of napalm getters based on install napalm version.
@@ -31,8 +23,13 @@ def get_napalm_getters() -> t.Dict[str, t.Dict[str, bool]]:
         >>> napalm_getters["eos"]["get_ipv6_neighbors_table"]  # doctest: +SKIP
         >>> False  # doctest: +SKIP
     """
-    if not HAS_NAPALM:
-        raise ImportError("Napalm must be install for this function to operate.")
+    try:
+        # Import NAPALM here at call time, rather than at import time, as importing NAPALM is rather time consuming
+        # pylint: disable=import-outside-toplevel
+        from napalm import get_network_driver
+        from napalm.base.exceptions import ModuleImportError
+    except ImportError as err:
+        raise ImportError("Napalm must be installed for this function to operate.") from err
 
     napalm_dict: t.Dict[str, t.Dict[str, bool]] = {}
     oses = NAPALM_LIB_MAPPER.keys()

tests/unit/test_lib_helpers.py

@@ -5,8 +5,8 @@
 from netutils.lib_helpers import get_napalm_getters
 
 
-@mock.patch("netutils.lib_helpers.HAS_NAPALM", False)
+@mock.patch.dict("sys.modules", {"napalm": None})
 def test_get_napalm_getters_napalm_not_installed():
     with pytest.raises(ImportError) as exc:
         get_napalm_getters()
-    assert "Napalm must be install for this function to operate." == str(exc.value)
+    assert "Napalm must be installed for this function to operate." == str(exc.value)

tests/unit/test_lib_helpers_optionals.py

@@ -7,7 +7,7 @@
 
 def test_get_napalm_getters_napalm_installed_default():
     pytest.importorskip("napalm")
-    with mock.patch("netutils.lib_helpers.get_network_driver"):
+    with mock.patch("napalm.get_network_driver"):
         napalm_getters = get_napalm_getters()
         assert all(item in napalm_getters.keys() for item in ["asa", "eos", "fortios"])