mirror of https://github.com/open-mmlab/mmcv.git
121 lines
2.9 KiB
Markdown
121 lines
2.9 KiB
Markdown
## File IO
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This module provides two universal API to load and dump files of different formats.
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### Load and dump data
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`mmcv` provides a universal api for loading and dumping data, currently
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supported formats are json, yaml and pickle.
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```python
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import mmcv
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# load data from a file
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data = mmcv.load('test.json')
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data = mmcv.load('test.yaml')
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data = mmcv.load('test.pkl')
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# load data from a file-like object
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with open('test.json', 'r') as f:
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data = mmcv.load(f)
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# dump data to a string
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json_str = mmcv.dump(data, format='json')
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# dump data to a file with a filename (infer format from file extension)
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mmcv.dump(data, 'out.pkl')
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# dump data to a file with a file-like object
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with open('test.yaml', 'w') as f:
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data = mmcv.dump(data, f, format='yaml')
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```
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It is also very convenient to extend the api to support more file formats.
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All you need to do is to write a file handler inherited from `BaseFileHandler`
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and register it with one or several file formats.
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You need to implement at least 3 methods.
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```python
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import mmcv
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# To register multiple file formats, a list can be used as the argument.
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# @mmcv.register_handler(['txt', 'log'])
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@mmcv.register_handler('txt')
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class TxtHandler1(mmcv.BaseFileHandler):
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def load_from_fileobj(self, file):
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return file.read()
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def dump_to_fileobj(self, obj, file):
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file.write(str(obj))
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def dump_to_str(self, obj, **kwargs):
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return str(obj)
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```
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Here is an example of `PickleHandler`.
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```python
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from six.moves import cPickle as pickle
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class PickleHandler(mmcv.BaseFileHandler):
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def load_from_fileobj(self, file, **kwargs):
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return pickle.load(file, **kwargs)
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def load_from_path(self, filepath, **kwargs):
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return super(PickleHandler, self).load_from_path(
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filepath, mode='rb', **kwargs)
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def dump_to_str(self, obj, **kwargs):
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kwargs.setdefault('protocol', 2)
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return pickle.dumps(obj, **kwargs)
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def dump_to_fileobj(self, obj, file, **kwargs):
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kwargs.setdefault('protocol', 2)
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pickle.dump(obj, file, **kwargs)
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def dump_to_path(self, obj, filepath, **kwargs):
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super(PickleHandler, self).dump_to_path(
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obj, filepath, mode='wb', **kwargs)
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```
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### Load a text file as a list or dict
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For example `a.txt` is a text file with 5 lines.
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```
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a
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b
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c
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d
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e
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```
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Then use `list_from_file` to load the list from a.txt.
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```python
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>>> mmcv.list_from_file('a.txt')
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['a', 'b', 'c', 'd', 'e']
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>>> mmcv.list_from_file('a.txt', offset=2)
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['c', 'd', 'e']
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>>> mmcv.list_from_file('a.txt', max_num=2)
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['a', 'b']
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>>> mmcv.list_from_file('a.txt', prefix='/mnt/')
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['/mnt/a', '/mnt/b', '/mnt/c', '/mnt/d', '/mnt/e']
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```
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For example `b.txt` is a text file with 5 lines.
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```
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1 cat
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2 dog cow
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3 panda
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```
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Then use `dict_from_file` to load the list from a.txt.
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```python
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>>> mmcv.dict_from_file('b.txt')
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{'1': 'cat', '2': ['dog', 'cow'], '3': 'panda'}
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>>> mmcv.dict_from_file('b.txt', key_type=int)
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{1: 'cat', 2: ['dog', 'cow'], 3: 'panda'}
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```
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