Import modules from a string list (#514)

* Custom imports

* Resolve comments

* Add unittest

* Add unittest

* Rename custom_imports to import_modules_from_strings

* Move import_modules_from_strings ito misc.py and allow failed imports

* small change

* small change

* change mmcv.runner to os.path

mmcv/utils/__init__.py

@@ -2,9 +2,9 @@
 # Copyright (c) Open-MMLab. All rights reserved.
 from .config import Config, ConfigDict, DictAction
 from .misc import (check_prerequisites, concat_list, deprecated_api_warning,
-                   is_list_of, is_seq_of, is_str, is_tuple_of, iter_cast,
-                   list_cast, requires_executable, requires_package,
-                   slice_list, tuple_cast)
+                   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)
 from .path import (check_file_exist, fopen, is_filepath, mkdir_or_exist,
                    scandir, symlink)
 from .progressbar import (ProgressBar, track_iter_progress,
@@ -23,7 +23,7 @@ except ImportError:
         'mkdir_or_exist', 'symlink', 'scandir', 'ProgressBar',
         'track_progress', 'track_iter_progress', 'track_parallel_progress',
         'Timer', 'TimerError', 'check_time', 'deprecated_api_warning',
-        'get_git_hash'
+        'get_git_hash', 'import_modules_from_strings'
     ]
 else:
     from .env import collect_env
@@ -47,5 +47,6 @@ else:
         '_AvgPoolNd', '_BatchNorm', '_ConvNd', '_ConvTransposeMixin',
         '_InstanceNorm', '_MaxPoolNd', 'get_build_config', 'BuildExtension',
         'CppExtension', 'CUDAExtension', 'DataLoader', 'PoolDataLoader',
-        'TORCH_VERSION', 'deprecated_api_warning', 'get_git_hash'
+        'TORCH_VERSION', 'deprecated_api_warning', 'get_git_hash',
+        'import_modules_from_strings'
     ]

mmcv/utils/misc.py

@@ -16,6 +16,54 @@ def is_str(x):
     return isinstance(x, str)
 
 
+def import_modules_from_strings(imports, allow_failed_imports=False):
+    """Import modules from the given list of strings.
+
+    Args:
+        imports (list | str | None): The given module names to be imported.
+        allow_failed_imports (bool): If True, the failed imports will return
+            None. Otherwise, an ImportError is raise. Default: False.
+
+    Returns:
+        list[module] | module | None: The imported modules.
+
+    Examples:
+        >>> osp, sys = import_modules_from_strings(
+        ...     ['os.path', 'sys'])
+        >>> import os.path as osp_
+        >>> import sys as sys_
+        >>> assert osp == osp_
+        >>> assert sys == sys_
+    """
+    if not imports:
+        return
+    single_import = False
+    if isinstance(imports, str):
+        single_import = True
+        imports = [imports]
+    if not isinstance(imports, list):
+        raise TypeError(
+            f'custom_imports must be a list but got type {type(imports)}')
+    imported = []
+    for imp in imports:
+        if not isinstance(imp, str):
+            raise TypeError(
+                f'{imp} is of type {type(imp)} and cannot be imported.')
+        try:
+            imported_tmp = import_module(imp)
+        except ImportError:
+            if allow_failed_imports:
+                warnings.warn(f'{imp} failed to import and is ignored.',
+                              UserWarning)
+                imported_tmp = None
+            else:
+                raise ImportError
+        imported.append(imported_tmp)
+    if single_import:
+        imported = imported[0]
+    return imported
+
+
 def iter_cast(inputs, dst_type, return_type=None):
     """Cast elements of an iterable object into some type.
 

tests/test_misc.py

@@ -100,3 +100,37 @@ def test_requires_executable(capsys):
         ' please install them first.\n')
 
     assert func_c() == 1
+
+
+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_
+    assert sys == sys_
+
+    # single imports
+    osp = mmcv.import_modules_from_strings('os.path')
+    assert osp == osp_
+    # No imports
+    assert mmcv.import_modules_from_strings(None) is None
+    assert mmcv.import_modules_from_strings([]) is None
+    assert mmcv.import_modules_from_strings('') is None
+    # Unsupported types
+    with pytest.raises(TypeError):
+        mmcv.import_modules_from_strings(1)
+    with pytest.raises(TypeError):
+        mmcv.import_modules_from_strings([1])
+    # Failed imports
+    with pytest.raises(ImportError):
+        mmcv.import_modules_from_strings('_not_implemented_module')
+    with pytest.warns(UserWarning):
+        imported = mmcv.import_modules_from_strings(
+            '_not_implemented_module', allow_failed_imports=True)
+        assert imported is None
+    with pytest.warns(UserWarning):
+        imported = mmcv.import_modules_from_strings(
+            ['os.path', '_not_implemented'], allow_failed_imports=True)
+        assert imported[0] == osp
+        assert imported[1] is None