Source code for soma.bufferandfile

# -*- coding: utf-8 -*-

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'''
:py:class:`BufferAndFile` instances are used to read data from a file (for
instance for identification) and "put back" the data on the file.

- author: Yann Cointepas
- organization: NeuroSpin
- license: `CeCILL B <http://www.cecill.info/licences/Licence_CeCILL-B_V1-en.html>`_
'''
__docformat__ = 'restructuredtext en'

#------------------------------------------------------------------------------


[docs]class BufferAndFile(object): ''' This class is a read only file-like object that allows to read ahead and push data back into the stream. All pushed back data are stored in a buffer that is "read" by all subsequent read acces until it is empty. When the buffer is empty, reading is done directly on the attached file object. Example:: from soma.bufferandfile import BufferAndFile # Open a file with a buffer f = BufferAndFile.open(fileName) # Check that the file content is XML start = f.read(5) # Put back the read characters f.unread( start ) if start == '<?xml': # Use the file in an XML parser ... elif start == '&HDF': # Use the file in an HDF5 parser ... ''' def __init__(self, file_object): ''' Create a file-like object that adds an :py:meth:`unread` method to an opened ``file_object``. ''' super(BufferAndFile, self).__init__() self.__buffer = '' self.__file = file_object self.name = getattr(file_object, 'name', '<unknown>')
[docs] def unread(self, string_value): ''' Adds data at the begining of the internal buffer. Data in the internal buffer will be returned by all subsequent read acces until the buffer is empty. ''' self.__buffer = string_value + self.__buffer
[docs] def change_file(self, file_object): ''' Change the internal file object (keeps the internal buffer untouched). ''' self.__file = file_object
[docs] def clone(self): ''' Return a new L{BufferAndFile} instance with the same internale buffer and the same internal file object as C{self}. ''' result = BufferAndFile(self.__file) result.__buffer = self.__buffer return result
[docs] def read(self, size=None): ''' Read the file ''' if size is None: result = self.__buffer + self.__file.read() else: buffer_size = len(self.__buffer) if buffer_size >= size: result = self.__buffer[:size] self.__buffer = self.__buffer[size:] else: result = self.__buffer + self.__file.read(size - buffer_size) self.__buffer = '' return result
[docs] def readline(self, size=None): ''' Read one text line ''' buffer_eol = self.__buffer.find('\n') if size is None: if buffer_eol < 0: result = self.__buffer + self.__file.readline() self.__buffer = '' else: buffer_eol += 1 result = self.__buffer[:buffer_eol] self.__buffer = self.__buffer[buffer_eol:] else: if buffer_eol < 0: buffer_size = len(self.__buffer) if buffer_size >= size: result = self.__buffer[:size] self.__buffer = self.__buffer[size:] else: result = self.__buffer + \ self.__file.readline(size - buffer_size) self.__buffer = '' else: size = min(size, buffer_eol + 1) result = self.__buffer[:size] self.__buffer = self.__buffer[size:] return result
def __iter__(self): ''' Iteration protocol ''' return self
[docs] def next(self): ''' Iteration protocol ''' line = self.readline() if not line: raise StopIteration return line
[docs] def tell(self): ''' Position in file ''' return self.__file.tell() - len(self.__buffer)
[docs] def seek(self, offset, whence=0): ''' If ``whence`` is 0 or 2 (absolute seek positioning) or if offset is negative, internal buffer is cleared and seek is done directly on the internal file object. Otherwise (relative seek with a positive offset), internal buffer is taken into account. ''' if whence == 2 or whence == 0 or offset < 0: self.__buffer = '' return self.__file.seek(offset, whence) else: buflen = len(self.__buffer) if offset > buflen: self.__buffer = '' return self.__file.seek(offset - buflen, whence) else: self.__buffer = self.__buffer[offset:]
[docs] def open(*args, **kwargs): ''' Open a file with built-in :py:func:`python:open` and create a :py:class:`BufferAndFile` instance. ''' return BufferAndFile(open(*args, **kwargs))
open = staticmethod(open)