Move is_installed from setup.py to jsonpickle.util so it can be used …

…to check for backends' existence.

jsonpickle/util.py

@@ -210,3 +210,19 @@ def is_picklable(name, value):
     if name in tags.RESERVED:
         return False
     return not is_function(value)
+
+def is_installed(module):
+    """Tests to see if ``module`` is available on the sys.path
+
+    >>> is_installed('sys')
+    True
+    >>> is_installed('hopefullythisisnotarealmodule')
+    False
+
+    """
+    try:
+        __import__(module)
+        return True
+    except ImportError, e:
+        return False
+

setup.py

@@ -47,17 +47,11 @@ def main():
 def _check_dependencies():
     # check to see if any of the supported backends is installed
     backends = _jsonpickle.SUPPORTED_BACKENDS
-    if not any([_is_installed(module) for module in backends]):
+    if not any([_jsonpickle.util.is_installed(module) for module in backends]):
         print >> sys.stderr, ('No supported JSON backend found. '
                               'Must install one of %s' % (', '.join(backends)))
         sys.exit(1)
 
-def _is_installed(module):
-    try:
-        __import__(module)
-        return True
-    except ImportError, e:
-        return False
 
 if __name__ == '__main__':
     sys.exit(main())