helper to check for C extension PYTHON-51

doc/api/pymongo/index.rst

@@ -9,6 +9,8 @@
 
       Alias for :class:`pymongo.connection.Connection`.
 
+   .. autofunction:: has_c
+
 Sub-modules:
 
 .. toctree::

pymongo/__init__.py

@@ -33,3 +33,12 @@ version = "1.4+"
 
 Connection = PyMongo_Connection
 """Alias for :class:`pymongo.connection.Connection`."""
+
+def has_c():
+    """Is the C extension installed?
+    """
+    try:
+        from pymongo import _cbson
+        return True
+    except ImportError:
+        return False

tools/fail_if_no_c.py

@@ -20,7 +20,7 @@ Only really intended to be used by internal build scripts.
 import sys
 sys.path[0:0] = [""]
 
-try:
-    from pymongo import _cbson
-except ImportError:
+import pymongo
+
+if not pymongo.has_c():
     sys.exit("could not import _cbson")