[bugfix] Minor improvements to apply_to_collection and type signatu…

…re of `log_dict` (#7851)

* minor fixeS

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
(cherry picked from commit 009e05d)

pytorch_lightning/core/lightning.py

@@ -25,7 +25,7 @@
 from argparse import Namespace
 from functools import partial
 from pathlib import Path
-from typing import Any, Callable, Dict, List, Optional, Sequence, Tuple, Union
+from typing import Any, Callable, Dict, List, Mapping, Optional, Sequence, Tuple, Union
 
 import torch
 from torch import ScriptModule, Tensor
@@ -347,7 +347,7 @@ def log(
 
     def log_dict(
         self,
-        dictionary: dict,
+        dictionary: Mapping[str, Any],
         prog_bar: bool = False,
         logger: bool = True,
         on_step: Optional[bool] = None,

pytorch_lightning/utilities/apply_func.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 import operator
 from abc import ABC
+from collections import OrderedDict
 from collections.abc import Mapping, Sequence
 from copy import copy
 from functools import partial
@@ -85,10 +86,12 @@ def apply_to_collection(
 
     # Recursively apply to collection items
     if isinstance(data, Mapping):
-        return elem_type({
-            k: apply_to_collection(v, dtype, function, *args, wrong_dtype=wrong_dtype, **kwargs)
-            for k, v in data.items()
-        })
+        return elem_type(
+            OrderedDict({
+                k: apply_to_collection(v, dtype, function, *args, wrong_dtype=wrong_dtype, **kwargs)
+                for k, v in data.items()
+            })
+        )
 
     if isinstance(data, tuple) and hasattr(data, '_fields'):  # named tuple
         return elem_type(

tests/utilities/test_apply_func.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import numbers
-from collections import namedtuple
+from collections import namedtuple, OrderedDict
 
 import numpy as np
 import torch
@@ -76,3 +76,19 @@ def test_recursive_application_to_collection():
 
     assert isinstance(reduced['g'], numbers.Number), 'Reduction of a number should result in a tensor'
     assert reduced['g'] == expected_result['g'], 'Reduction of a number did not yield the desired result'
+
+    # mapping support
+    reduced = apply_to_collection({'a': 1, 'b': 2}, int, lambda x: str(x))
+    assert reduced == {'a': '1', 'b': '2'}
+    reduced = apply_to_collection(OrderedDict([('b', 2), ('a', 1)]), int, lambda x: str(x))
+    assert reduced == OrderedDict([('b', '2'), ('a', '1')])
+
+    # custom mappings
+    class _CustomCollection(dict):
+
+        def __init__(self, initial_dict):
+            super().__init__(initial_dict)
+
+    to_reduce = _CustomCollection({'a': 1, 'b': 2, 'c': 3})
+    reduced = apply_to_collection(to_reduce, int, lambda x: str(x))
+    assert reduced == _CustomCollection({'a': '1', 'b': '2', 'c': '3'})