[Fix] Fix dump config without self.filename (#202)

* fix config

* add docstring and unit test

* update tutorial

* update tutorial

* fix markdown format

* fix markdown format

docs/zh_cn/tutorials/config.md

@@ -194,6 +194,71 @@ a = {{_base_.model}}
 # 等价于 a = dict(type='ResNet', depth=50)
 ```
 
+## 配置文件的导出
+
+在启动训练脚本时，用户可能通过传参的方式来修改配置文件的部分字段，为此我们提供了 `dump`
+接口来导出更改后的配置文件。与读取配置文件类似，用户可以通过 `cfg.dump('config.xxx')` 来选择导出文件的格式。`dump`
+同样可以导出有继承关系的配置文件，导出的文件可以被独立使用，不再依赖于 `_base_` 中定义的文件。
+
+基于继承一节定义的 `resnet50.py`
+
+```python
+_base_ = ['optimizer_cfg.py', 'runtime_cfg.py']
+model = dict(type='ResNet', depth=50)
+```
+
+我们将其加载后导出:
+
+```python
+cfg = Config.fromfile('resnet50.py')
+cfg.dump('resnet50_dump.py')
+```
+
+`dumped_resnet50.py`
+
+```python
+optimizer = dict(type='SGD', lr=0.02, momentum=0.9, weight_decay=0.0001)
+gpu_ids = [0, 1]
+model = dict(type='ResNet', depth=50)
+```
+
+类似的，我们可以导出 json、yaml 格式的配置文件
+
+`dumped_resnet50.yaml`
+
+```yaml
+gpu_ids:
+- 0
+- 1
+model:
+  depth: 50
+  type: ResNet
+optimizer:
+  lr: 0.02
+  momentum: 0.9
+  type: SGD
+  weight_decay: 0.0001
+```
+
+`dumped_resnet50.json`
+
+```json
+{"optimizer": {"type": "SGD", "lr": 0.02, "momentum": 0.9, "weight_decay": 0.0001}, "gpu_ids": [0, 1], "model": {"type": "ResNet", "depth": 50}}
+```
+
+此外，`dump` 不仅能导出加载自文件的 `cfg`，还能导出加载自字典的 `cfg`
+
+```python
+cfg = Config(dict(a=1, b=2))
+cfg.dump('demo.py')
+```
+
+`demo.py`
+```python
+a=1
+b=2
+```
+
 ## 其他进阶用法
 
 这里介绍一下配置类的进阶用法，这些小技巧可能使用户开发和使用算法库更简单方便。

mmengine/config/config.py

@@ -12,6 +12,7 @@ import warnings
 from argparse import Action, ArgumentParser, Namespace
 from collections import abc
 from importlib import import_module
+from pathlib import Path
 from typing import Any, Optional, Sequence, Tuple, Union
 
 from addict import Dict
@@ -99,7 +100,8 @@ class Config:
     Args:
         cfg_dict (dict, optional): A config dictionary. Defaults to None.
         cfg_text (str, optional): Text of config. Defaults to None.
-        filename (str, optional): Name of config file. Defaults to None.
+        filename (str or Path, optional): Name of config file.
+            Defaults to None.
 
     Examples:
         >>> cfg = Config(dict(a=1, b=dict(b1=[0, 1])))
@@ -123,7 +125,8 @@ class Config:
     def __init__(self,
                  cfg_dict: dict = None,
                  cfg_text: Optional[str] = None,
-                 filename: str = None):
+                 filename: Optional[Union[str, Path]] = None):
+        filename = str(filename) if isinstance(filename, Path) else filename
         if cfg_dict is None:
             cfg_dict = dict()
         elif not isinstance(cfg_dict, dict):
@@ -145,13 +148,13 @@ class Config:
         super().__setattr__('_text', text)
 
     @staticmethod
-    def fromfile(filename: str,
+    def fromfile(filename: Union[str, Path],
                  use_predefined_variables: bool = True,
                  import_custom_modules: bool = True) -> 'Config':
         """Build a Config instance from config file.
 
         Args:
-            filename (str): Name of config file.
+            filename (str or Path): Name of config file.
             use_predefined_variables (bool, optional): Whether to use
                 predefined variables. Defaults to True.
             import_custom_modules (bool, optional): Whether to support
@@ -160,6 +163,7 @@ class Config:
         Returns:
             Config: Config instance built from config file.
         """
+        filename = str(filename) if isinstance(filename, Path) else filename
         cfg_dict, cfg_text = Config._file2dict(filename,
                                                use_predefined_variables)
         if import_custom_modules and cfg_dict.get('custom_imports', None):
@@ -675,32 +679,31 @@ class Config:
         super().__setattr__('_filename', _filename)
         super().__setattr__('_text', _text)
 
-    def dump(self, file: Optional[str] = None):
+    def dump(self, file: Optional[Union[str, Path]] = None):
         """Dump config to file or return config text.
 
         Args:
-            file (str, optional): If not specified, then the object
+            file (str or Path, optional): If not specified, then the object
             is dumped to a str, otherwise to a file specified by the filename.
             Defaults to None.
 
         Returns:
             str or None: Config text.
         """
-        cfg_dict = super().__getattribute__('_cfg_dict').to_dict()
-        if self.filename.endswith('.py'):
-            if file is None:
+        file = str(file) if isinstance(file, Path) else file
+        cfg_dict = super(Config, self).__getattribute__('_cfg_dict').to_dict()
+        if file is None:
+            if self.filename is None or self.filename.endswith('.py'):
                 return self.pretty_text
             else:
-                with open(file, 'w', encoding='utf-8') as f:
-                    f.write(self.pretty_text)
-                return None
-        else:
-            if file is None:
                 file_format = self.filename.split('.')[-1]
                 return dump(cfg_dict, file_format=file_format)
-            else:
-                dump(cfg_dict, file)
-                return None
+        elif file.endswith('.py'):
+            with open(file, 'w', encoding='utf-8') as f:
+                f.write(self.pretty_text)
+        else:
+            file_format = file.split('.')[-1]
+            return dump(cfg_dict, file=file, file_format=file_format)
 
     def merge_from_dict(self,
                         options: dict,

tests/test_config/test_config.py

@@ -224,8 +224,26 @@ class TestConfig:
         pkl_cfg_filename = tmp_path / '_pickle.pkl'
         dump(cfg, pkl_cfg_filename)
         pkl_cfg = load(pkl_cfg_filename)
-
         assert pkl_cfg._cfg_dict == cfg._cfg_dict
+        # Test dump config from dict.
+        cfg_dict = dict(a=1, b=2)
+        cfg = Config(cfg_dict)
+        assert cfg.pretty_text == cfg.dump()
+        # Test dump python format config.
+        dump_file = tmp_path / 'dump_from_dict.py'
+        cfg.dump(dump_file)
+        with open(dump_file, 'r') as f:
+            assert f.read() == 'a = 1\nb = 2\n'
+        # Test dump json format config.
+        dump_file = tmp_path / 'dump_from_dict.json'
+        cfg.dump(dump_file)
+        with open(dump_file, 'r') as f:
+            assert f.read() == '{"a": 1, "b": 2}'
+        # Test dump yaml format config.
+        dump_file = tmp_path / 'dump_from_dict.yaml'
+        cfg.dump(dump_file)
+        with open(dump_file, 'r') as f:
+            assert f.read() == 'a: 1\nb: 2\n'
 
     def test_pretty_text(self, tmp_path):
         cfg_file = osp.join(