[Enhancement] Add to_ntuple (#1125)

* add to_ntuple

* add unit test

mmcv/utils/__init__.py

@@ -4,7 +4,8 @@ from .config import Config, ConfigDict, DictAction
 from .misc import (check_prerequisites, concat_list, deprecated_api_warning,
                    import_modules_from_strings, is_list_of, is_seq_of, is_str,
                    is_tuple_of, iter_cast, list_cast, requires_executable,
-                   requires_package, slice_list, tuple_cast)
+                   requires_package, slice_list, to_1tuple, to_2tuple,
+                   to_3tuple, to_4tuple, to_ntuple, tuple_cast)
 from .path import (check_file_exist, fopen, is_filepath, mkdir_or_exist,
                    scandir, symlink)
 from .progressbar import (ProgressBar, track_iter_progress,
@@ -29,17 +30,18 @@ except ImportError:
         'Timer', 'TimerError', 'check_time', 'deprecated_api_warning',
         'digit_version', 'get_git_hash', 'import_modules_from_strings',
         'assert_dict_contains_subset', 'assert_attrs_equal',
-        'assert_dict_has_keys', 'assert_keys_equal', 'check_python_script'
+        'assert_dict_has_keys', 'assert_keys_equal', 'check_python_script',
+        'to_1tuple', 'to_2tuple', 'to_3tuple', 'to_4tuple', 'to_ntuple'
     ]
 else:
     from .env import collect_env
     from .logging import get_logger, print_log
+    from .parrots_jit import jit, skip_no_elena
     from .parrots_wrapper import (
         CUDA_HOME, TORCH_VERSION, BuildExtension, CppExtension, CUDAExtension,
         DataLoader, PoolDataLoader, SyncBatchNorm, _AdaptiveAvgPoolNd,
         _AdaptiveMaxPoolNd, _AvgPoolNd, _BatchNorm, _ConvNd,
         _ConvTransposeMixin, _InstanceNorm, _MaxPoolNd, get_build_config)
-    from .parrots_jit import jit, skip_no_elena
     from .registry import Registry, build_from_cfg
     __all__ = [
         'Config', 'ConfigDict', 'DictAction', 'collect_env', 'get_logger',

mmcv/utils/misc.py

 # Copyright (c) Open-MMLab. All rights reserved.
+import collections.abc
 import functools
 import itertools
 import subprocess
@@ -6,6 +7,25 @@ import warnings
 from collections import abc
 from importlib import import_module
 from inspect import getfullargspec
+from itertools import repeat
+
+
+# From PyTorch internals
+def _ntuple(n):
+
+    def parse(x):
+        if isinstance(x, collections.abc.Iterable):
+            return x
+        return tuple(repeat(x, n))
+
+    return parse
+
+
+to_1tuple = _ntuple(1)
+to_2tuple = _ntuple(2)
+to_3tuple = _ntuple(3)
+to_4tuple = _ntuple(4)
+to_ntuple = _ntuple
 
 
 def is_str(x):

tests/test_utils/test_misc.py

@@ -4,6 +4,31 @@ import pytest
 import mmcv
 
 
+def test_to_ntuple():
+    single_number = 2
+    assert mmcv.utils.to_1tuple(single_number) == (single_number, )
+    assert mmcv.utils.to_2tuple(single_number) == (single_number,
+                                                   single_number)
+    assert mmcv.utils.to_3tuple(single_number) == (single_number,
+                                                   single_number,
+                                                   single_number)
+    assert mmcv.utils.to_4tuple(single_number) == (single_number,
+                                                   single_number,
+                                                   single_number,
+                                                   single_number)
+    assert mmcv.utils.to_ntuple(5)(single_number) == (single_number,
+                                                      single_number,
+                                                      single_number,
+                                                      single_number,
+                                                      single_number)
+    assert mmcv.utils.to_ntuple(6)(single_number) == (single_number,
+                                                      single_number,
+                                                      single_number,
+                                                      single_number,
+                                                      single_number,
+                                                      single_number)
+
+
 def test_iter_cast():
     assert mmcv.list_cast([1, 2, 3], int) == [1, 2, 3]
     assert mmcv.list_cast(['1.1', 2, '3'], float) == [1.1, 2.0, 3.0]
@@ -105,6 +130,7 @@ def test_requires_executable(capsys):
 def test_import_modules_from_strings():
     # multiple imports
     import os.path as osp_
+
     import sys as sys_
     osp, sys = mmcv.import_modules_from_strings(['os.path', 'sys'])
     assert osp == osp_