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"""
fs.contrib.bigfs.subrangefile
=============================
A file-like object that allows wrapping of part of a binary file for reading.
This avoids needless copies of data for large binary files if StringIO would
be used.
Written by Koen van de Sande
http://www.tibed.net
Contributed under the terms of the BSD License:
http://www.opensource.org/licenses/bsd-license.php
"""
class SubrangeFile:
"""File-like class with read-only, binary mode restricting access to a subrange of the whole file"""
def __init__(self, f, startOffset, fileSize):
if not hasattr(f, 'read'):
self.f = open(f, "rb")
self.name = f
else:
self.f = f
self.name = str(f)
self.startOffset = startOffset
self.fileSize = fileSize
self.seek(0)
def __str__(self):
return "<SubrangeFile: %s@%d size=%d>" % (self.name, self.startOffset, self.fileSize)
def __unicode__(self):
return unicode(self.__str__())
def size(self):
return self.fileSize
def seek(self, offset, whence=0):
if whence == 0:
offset = self.startOffset + offset
elif whence == 1:
offset = self.startOffset + self.tell() + offset
elif whence == 2:
if offset > 0:
offset = 0
offset = self.startOffset + self.fileSize + offset
self.f.seek(offset)
def tell(self):
return self.f.tell() - self.startOffset
def __maxSize(self,size=None):
iSize = self.fileSize
if not size is None:
if size < iSize:
iSize = size
if self.tell() + iSize > self.fileSize:
iSize = self.fileSize - self.tell()
return iSize
def readline(self,size=None):
toRead = self.__maxSize(size)
return self.f.readline(toRead)
def read(self,size=None):
toRead = self.__maxSize(size)
return self.f.read(toRead)
def readlines(self,size=None):
toRead = self.__maxSize(size)
temp = self.f.readlines(toRead)
# now cut off more than we should read...
result = []
counter = 0
for line in temp:
if counter + len(line) > toRead:
if toRead == counter:
break
result.append(line[0:(toRead-counter)])
break
else:
result.append(line)
counter += len(line)
return result
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