fix(new.py): Directly raise an ImportError if new.py is attempted to be imported by a user without multidict being installed.

Author: rbeyer

HISTORY.rst

@@ -30,6 +30,11 @@ and the release date, in year-month-day format (see examples below).
 Unreleased
 ----------
 
+Fixed
++++++
+* Attempting to import pvl/new.py without multidict being available,
+  will now properly yield an ImportError.
+
 1.2.0 (2021-03-27)
 ------------------
 

Makefile

@@ -46,6 +46,9 @@ lint:
 test:
 	python -m pytest --doctest-modules --doctest-glob='*.rst'
 
+test-min:
+	python -m pytest --doctest-modules --ignore=pvl/new.py
+
 test-all:
 	tox
 

pvl/new.py

@@ -26,6 +26,18 @@
 import inspect
 import urllib.request
 
+try:  # noqa: C901
+    # In order to access super class attributes for our derived class, we must
+    # import the native Python version, instead of the default Cython version.
+    from multidict._multidict_py import MultiDict
+except ImportError as err:
+    raise ImportError(
+        "The multidict library is not present, so the new PVLMultiDict is not "
+        "available, and pvl.new can't be imported. In order to do so, install "
+        "the multidict package",
+        ImportWarning,
+    ) from err
+
 from pvl import *  # noqa: F401,F403
 from pvl import get_text_from, decode_by_char