Merge pull request scipy#16304 from rgommers/ccallback-errmsg

MAINT: add a more informative error message for broken installs

scipy/__init__.py

@@ -145,7 +145,17 @@
                       UserWarning)
     del _pep440
 
-    from scipy._lib._ccallback import LowLevelCallable
+    # This is the first import of an extension module within SciPy. If there's
+    # a general issue with the install, such that extension modules are missing
+    # or cannot be imported, this is where we'll get a failure - so give an
+    # informative error message.
+    try:
+        from scipy._lib._ccallback import LowLevelCallable
+    except ImportError as e:
+        msg = "The `scipy` install you are using seems to be broken, " + \
+              "(extension modules cannot be imported), " + \
+              "please try reinstalling."
+        raise ImportError(msg) from e
 
     from scipy._lib._testutils import PytestTester
     test = PytestTester(__name__)