how to remove n bytes in a file?

[Tim Chase]

> def shift(f, offset, size, buffer_size=1024*1024):

Slight bug in that function implementation.  This one passes my 
tests.

Sorry about that.

-tkc


def shift(f, offset, size, buffer_size=1024*1024):
	"""deletes (in place) a portion of size "size" from file "f", 
starting at offset "offset"

The buffer_size can be tweaked for system preferences,
defaulting to 1 megabyte.
"""

	f.seek(offset + size)
	while True:
		buffer = f.read(buffer_size)
		if not buffer: break
		f.seek(offset)
		f.write(buffer)
		offset += buffer_size
		f.seek(offset + size)
	f.seek(-size,2)
	f.truncate()

if __name__ == '__main__':
	offset = ord('p')
	size = 5
	buffer_size = 10

	from StringIO import StringIO
	s = ''.join([chr(i) for i in xrange(256)])
	print repr(s)
	print "="*50
	f = StringIO(s)
	# delete "p" through "u"
	shift(f, offset, size, buffer_size)
	f.seek(0)
	result = f.read()
	print repr(result)