Replacing ValueError with InvalidArgumentError in google.gax.errors.c…

…reate_error(). (#196)

This new class inherits from both GaxError and ValueError to keep
from breaking existing clients.

By wrapping an `INVALID_ARGUMENT` in a `ValueError`, the impl. was losing
information by "stringify"-ing the wrapped exception.

See #132 for change that introduced the `ValueError` behavior.

google/gax/errors.py

@@ -52,26 +52,42 @@ def __str__(self):
         if not self.cause:
             return msg
 
-        return 'GaxError({}, caused by {})'.format(msg, self.cause)
+        return '{}({}, caused by {})'.format(
+            self.__class__.__name__, msg, self.cause)
 
 
-def create_error(msg, cause=None):
-    """Creates an error.
-
-    Uses a Python built-in exception if one is available, and a
-    GaxError otherwise.
+class InvalidArgumentError(ValueError, GaxError):
+    """GAX exception class for ``INVALID_ARGUMENT`` errors.
 
     Attributes:
       msg (string): describes the error that occurred.
       cause (Exception, optional): the exception raised by a lower
         layer of the RPC stack (for example, gRPC) that caused this
         exception, or None if this exception originated in GAX.
     """
-    if config.NAME_STATUS_CODES.get(
-            config.exc_to_code(cause)) == 'INVALID_ARGUMENT':
-        return ValueError('{}: {}'.format(msg, cause))
+
+    def __init__(self, msg, cause=None):
+        GaxError.__init__(self, msg, cause=cause)
+
+
+def create_error(msg, cause=None):
+    """Creates a ``GaxError`` or subclass.
+
+    Attributes:
+        msg (string): describes the error that occurred.
+        cause (Exception, optional): the exception raised by a lower
+            layer of the RPC stack (for example, gRPC) that caused this
+            exception, or None if this exception originated in GAX.
+
+    Returns:
+        .GaxError: The exception that wraps ``cause``.
+    """
+    status_code = config.exc_to_code(cause)
+    status_name = config.NAME_STATUS_CODES.get(status_code)
+    if status_name == 'INVALID_ARGUMENT':
+        return InvalidArgumentError(msg, cause=cause)
     else:
-        return GaxError(msg, cause)
+        return GaxError(msg, cause=cause)
 
 
 class RetryError(GaxError):

tests/test_api_callable.py

@@ -438,6 +438,7 @@ def other_error_func(*dummy_args, **dummy_kwargs):
         self.assertRaises(AnotherException, other_error_callable, None)
 
     def test_wrap_value_error(self):
+        from google.gax.errors import InvalidArgumentError
 
         invalid_attribute_exc = grpc.RpcError()
         invalid_attribute_exc.code = lambda: grpc.StatusCode.INVALID_ARGUMENT
@@ -447,4 +448,10 @@ def value_error_func(*dummy_args, **dummy_kwargs):
 
         value_error_callable = api_callable.create_api_call(
             value_error_func, _CallSettings())
-        self.assertRaises(ValueError, value_error_callable, None)
+
+        with self.assertRaises(ValueError) as exc_info:
+            value_error_callable(None)
+
+        self.assertIsInstance(exc_info.exception, InvalidArgumentError)
+        self.assertEqual(exc_info.exception.args, (u'RPC failed',))
+        self.assertIs(exc_info.exception.cause, invalid_attribute_exc)