import_modules_from_strings when loading cfg from file (open-mmlab#606)

* import_modules_from_strings when loading cfg from file

* add unittest to tell whether the feature is enabled as expected

* minor

* set an environment variable instead of writing a file

* use 'shutil' instead of 'os.system'

mmcv/utils/config.py

@@ -12,6 +12,7 @@
 from addict import Dict
 from yapf.yapflib.yapf_api import FormatCode
 
+from .misc import import_modules_from_strings
 from .path import check_file_exist
 
 if platform.system() == 'Windows':
@@ -208,9 +209,13 @@ def _merge_a_into_b(a, b):
         return b
 
     @staticmethod
-    def fromfile(filename, use_predefined_variables=True):
+    def fromfile(filename,
+                 use_predefined_variables=True,
+                 import_custom_modules=True):
         cfg_dict, cfg_text = Config._file2dict(filename,
                                                use_predefined_variables)
+        if import_custom_modules and cfg_dict.get('custom_imports', None):
+            import_modules_from_strings(**cfg_dict['custom_imports'])
         return Config(cfg_dict, cfg_text=cfg_text, filename=filename)
 
     @staticmethod

tests/data/config/q.py

@@ -0,0 +1,3 @@
+custom_imports = dict(
+    imports=['r'],
+    allow_failed_imports=False)

tests/data/config/r.py

@@ -0,0 +1,3 @@
+import os
+
+os.environ["TEST_VALUE"] = 'test'

tests/test_utils/test_config.py

@@ -1,7 +1,9 @@
 # Copyright (c) Open-MMLab. All rights reserved.
 import argparse
 import json
+import os
 import os.path as osp
+import shutil
 import tempfile
 
 import pytest
@@ -140,6 +142,19 @@ def test_fromfile():
         assert cfg.text == osp.abspath(osp.expanduser(cfg_file)) + '\n' + \
             open(cfg_file, 'r').read()
 
+    # test custom_imports for Config.fromfile
+    cfg_file = osp.join(data_path, 'config', 'q.py')
+    imported_file = osp.join(data_path, 'config', 'r.py')
+    target_pkg = osp.join(osp.dirname(__file__), 'r.py')
+
+    # Since the imported config will be regarded as a tmp file
+    # it should be copied to the directory at the same level
+    shutil.copy(imported_file, target_pkg)
+    Config.fromfile(cfg_file, import_custom_modules=True)
+
+    assert os.environ.pop('TEST_VALUE') == 'test'
+    os.remove(target_pkg)
+
     with pytest.raises(FileNotFoundError):
         Config.fromfile('no_such_file.py')
     with pytest.raises(IOError):