Clean up ECDriver

 - Add a docstring, since I can never remember the **kwargs.
 - Drop the (unused) *args.
 - Raise an error earlier if neither ec_type nor library_import_str
   is provided.

Change-Id: I38b71ede59b6b0e249223792207b0f48438f7b97

2 files changed, 31 insertions, 5 deletions

diff --git a/pyeclib/ec_iface.py b/pyeclib/ec_iface.py
index 59bf1fb..cc9c516 100644
--- a/pyeclib/ec_iface.py
+++ b/pyeclib/ec_iface.py
@@ -142,8 +142,22 @@ class PyECLib_FRAGHDRCHKSUM_Types(PyECLibEnum):
 
 # Main ECDriver class
 class ECDriver(object):
-
-    def __init__(self, *args, **kwargs):
+    '''A driver to encode, decode, and reconstruct erasure-coded data.'''
+
+    def __init__(self, **kwargs):
+        '''
+        :param ec_type: the erasure coding type to use for this driver.
+        :param k: number of data fragments to use. Required.
+        :param m: number of parity fragments to use. Required.
+        :param chksum_type:
+        :param validate: default: False
+        :param library_import_str: default: 'pyeclib.core.ECPyECLibDriver'
+
+        You must provide either ``ec_type`` or ``library_import_str``;
+        typically you just want to use ``ec_type``. See ALL_EC_TYPES for the
+        list of all EC types supported by PyECLib, and VALID_EC_TYPES for the
+        list of all EC types currently available on this system.
+        '''
         self.k = -1
         self.m = -1
         self.hd = -1
@@ -156,6 +170,11 @@ class ECDriver(object):
                 raise ECDriverError(
                     "Invalid Argument: %s is required" % required)
 
+        if 'ec_type' not in kwargs and 'library_import_str' not in kwargs:
+            raise ECDriverError(
+                "Invalid Argument: either ec_type or library_import_str "
+                "must be provided")
+
         for (key, value) in kwargs.items():
             if key == "k":
                 try:
diff --git a/test/test_pyeclib_api.py b/test/test_pyeclib_api.py
index 9585035..085a480 100644
--- a/test/test_pyeclib_api.py
+++ b/test/test_pyeclib_api.py
@@ -117,22 +117,29 @@ class TestPyECLibDriver(unittest.TestCase):
     def tearDown(self):
         pass
 
-    def test_invalid_km_args(self):
+    def test_missing_required_args(self):
+        # missing ec_type
+        with self.assertRaises(ECDriverError) as err_context:
+            ECDriver(k=1, m=1)
+        self.assertEqual(str(err_context.exception),
+                         "Invalid Argument: either ec_type or "
+                         "library_import_str must be provided")
+
         for ec_type in VALID_EC_TYPES:
             # missing k
             with self.assertRaises(ECDriverError) as err_context:
                 ECDriver(ec_type=ec_type, m=1)
-
             self.assertEqual(str(err_context.exception),
                              "Invalid Argument: k is required")
 
             # missing m
             with self.assertRaises(ECDriverError) as err_context:
                 ECDriver(ec_type=ec_type, k=1)
-
             self.assertEqual(str(err_context.exception),
                              "Invalid Argument: m is required")
 
+    def test_invalid_km_args(self):
+        for ec_type in VALID_EC_TYPES:
             with self.assertRaises(ECDriverError) as err_context:
                 # k is smaller than 1
                 ECDriver(ec_type=ec_type, k=-100, m=1)