107 lines
3.4 KiB
Python
107 lines
3.4 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2013 Google Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""FilePart implementation for representing part of a file."""
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from __future__ import absolute_import
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from __future__ import print_function
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from __future__ import division
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from __future__ import unicode_literals
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import os
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import io
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class FilePart(io.IOBase):
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"""Subclass of the file API for representing part of a file.
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This class behaves as a contiguous subset of a given file (e.g., this object
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will behave as though the desired part of the file was written to another
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file, and the second file was opened).
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"""
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# pylint: disable=super-init-not-called
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def __init__(self, filename, offset, length):
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"""Initializes the FilePart.
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Args:
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filename: The name of the existing file, of which this object represents
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a part.
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offset: The position (in bytes) in the original file that corresponds to
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the first byte of the FilePart.
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length: The total number of bytes in the FilePart.
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"""
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self._fp = open(filename, 'rb')
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self.length = length
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self._start = offset
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self._end = self._start + self.length
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self._fp.seek(self._start)
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def __enter__(self):
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pass
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# pylint: disable=redefined-builtin
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def __exit__(self, type, value, traceback):
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self.close()
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def tell(self):
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return self._fp.tell() - self._start
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def read(self, size=-1):
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if size < 0:
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size = self.length
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size = min(size, self._end - self._fp.tell()) # Only read to our EOF
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return self._fp.read(max(0, size))
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def seek(self, offset, whence=os.SEEK_SET):
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if whence == os.SEEK_END:
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return self._fp.seek(offset + self._end)
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elif whence == os.SEEK_CUR:
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return self._fp.seek(offset, whence)
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else:
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return self._fp.seek(self._start + offset)
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def close(self):
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self._fp.close()
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def flush(self, size=None):
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raise NotImplementedError('flush is not implemented in FilePart.')
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def fileno(self, size=None):
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raise NotImplementedError('fileno is not implemented in FilePart.')
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def isatty(self, size=None):
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raise NotImplementedError('isatty is not implemented in FilePart.')
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def next(self, size=None):
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raise NotImplementedError('next is not implemented in FilePart.')
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def readline(self, size=None):
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raise NotImplementedError('readline is not implemented in FilePart.')
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def readlines(self, size=None):
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raise NotImplementedError('readlines is not implemented in FilePart.')
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def xreadlines(self, size=None):
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raise NotImplementedError('xreadlines is not implemented in FilePart.')
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def truncate(self, size=None):
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raise NotImplementedError('truncate is not implemented in FilePart.')
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def write(self, size=None):
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raise NotImplementedError('write is not implemented in FilePart.')
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def writelines(self, size=None):
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raise NotImplementedError('writelines is not implemented in FilePart.')
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