Paul Probert wrote:

I'm trying to write numpy arrays as binary data, to support a legacy file format. So I open a file and write to it:

fp = open('somefile','w') ... oldpos = fp.tell() somenumpyarray.tofile(fp) newpos = fp.tell() diff = newpos - oldpos - somenumpyarray.nbytes if diff != 0: print 'ahhah! mismatch=',diff ...

I'm observing that every once in while I get 'ahhah! mismatch=1', that is, the file position is advanced by one more byte than x.nbytes would give. I'm using 1.4.1 on windows, python 2.5. Any ideas?

yup -- you need to open your file as binary: fp = open('somefile','wb') python is adding a carriage return when it sees a newline, to conform to windows text file conventions. -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception Chris.Barker@noaa.gov