On 25/05/2011 20:33, tkp...@hotmail.com wrote:
The following function that returns the last line of a file works perfectly well under Python 2.71. but fails reliably under Python 3.2. Is this a bug, or am I doing something wrong? Any help would be greatly appreciated.import os def lastLine(filename): ''' Returns the last line of a file file.seek takes an optional 'whence' argument which allows you to start looking at the end, so you can just work back from there till you hit the first newline that has anything after it Works perfectly under Python 2.7, but not under 3.2! ''' offset = -50 with open(filename) as f: while offset> -1024: offset *= 2 f.seek(offset, os.SEEK_END) lines = f.readlines() if len(lines)> 1: return lines[-1] If I execute this with a valid filename fn. I get the following error message:lastLine(fn)Traceback (most recent call last): File "<pyshell#12>", line 1, in<module> lastLine(fn) File "<pyshell#11>", line 13, in lastLine f.seek(offset, os.SEEK_END) io.UnsupportedOperation: can't do nonzero end-relative seeks
You're opening the file in text mode, and seeking relative to the end of the file is not allowed in text mode, presumably because the file contents have to be decoded, and, in general, seeking to an arbitrary position within a sequence of encoded bytes can have undefined results when you attempt to decode to Unicode starting from that position. The strange thing is that you _are_ allowed to seek relative to the start of the file. Try opening the file in binary mode and do the decoding yourself, catching the DecodeError exceptions if/when they occur. -- http://mail.python.org/mailman/listinfo/python-list
