1 files changed, 7 insertions, 3 deletions
diff --git a/tools/cythonize.py b/tools/cythonize.py
index 6cebf0f72..06cf54c9a 100755
--- a/tools/cythonize.py
+++ b/tools/cythonize.py
@@ -56,12 +56,14 @@ def process_pyx(fromfile, tofile):
 
     try:
         # try the cython in the installed python first (somewhat related to scipy/scipy#2397)
+        import Cython
         from Cython.Compiler.Version import version as cython_version
-    except ImportError:
+    except ImportError as e:
         # The `cython` command need not point to the version installed in the
         # Python running this script, so raise an error to avoid the chance of
         # using the wrong version of Cython.
-        raise OSError('Cython needs to be installed in Python as a module')
+        msg = 'Cython needs to be installed in Python as a module'
+        raise OSError(msg) from e
     else:
         # check the version, and invoke through python
         from distutils.version import LooseVersion
@@ -73,7 +75,9 @@ def process_pyx(fromfile, tofile):
         required_version = LooseVersion('0.29.21')
 
         if LooseVersion(cython_version) < required_version:
-            raise RuntimeError(f'Building {VENDOR} requires Cython >= {required_version}')
+            cython_path = Cython.__file__
+            raise RuntimeError(f'Building {VENDOR} requires Cython >= {required_version}'
+                               f', found {cython_version} at {cython_path}')
         subprocess.check_call(
             [sys.executable, '-m', 'cython'] + flags + ["-o", tofile, fromfile])