fix abstract type hint (#2753)

Author: DeNeutoy

allennlp/nn/initializers.py

@@ -25,7 +25,7 @@
 import logging
 import re
 import math
-from typing import Callable, List, Tuple, Type, Iterable, Dict
+from typing import Callable, List, Tuple, Type, Dict
 import itertools
 from overrides import overrides
 
@@ -314,7 +314,7 @@ def __call__(self, module: torch.nn.Module) -> None:
             logger.info("   %s", name)
 
     @classmethod
-    def from_params(cls, params: Iterable[Tuple[str, Params]] = ()) -> "InitializerApplicator":  # type: ignore
+    def from_params(cls, params: List[Tuple[str, Params]] = None) -> "InitializerApplicator":
         """
         Converts a Params object into an InitializerApplicator. The json should
         be formatted as follows::
@@ -345,7 +345,7 @@ def from_params(cls, params: Iterable[Tuple[str, Params]] = ()) -> "InitializerA
         An InitializerApplicator containing the specified initializers.
         """
         # pylint: disable=arguments-differ
-
+        params = params or []
         is_prevent = lambda item: item == "prevent" or item == {"type": "prevent"}
         prevent_regexes = [param[0] for param in params if is_prevent(param[1])]
         params = [param for param in params if param[1] if not is_prevent(param[1])]

allennlp/tests/nn/initializers_test.py

@@ -26,6 +26,9 @@ def tearDown(self):
     def test_from_params_string(self):
         Initializer.from_params(params="eye")
 
+    def test_from_params_none(self):
+        Initializer.from_params(params=None)
+
     def test_regex_matches_are_initialized_correctly(self):
         class Net(torch.nn.Module):
             def __init__(self):