you have to use the offset keyword argument of np.memmap, else it will always start from the beginning of the file
>>> np.memmap(fd, dtype="float32", mode="r", offset=offset) On Thu, Oct 10, 2013 at 2:43 PM, Andreas Hilboll <li...@hilboll.de> wrote: > Hi, > > I have a problem using memmap correctly. I need to read a data file > which consists of an ASCII header and appended binary single precision > floating point values. memmap complains that the "Size of available data > is not a multiple of the data-type size." But as far as I can tell, the > size *doas* match the data-type size. > > The problem is illustrated by the following code: > > ---8<------- > > url = "http://www.iup.uni-bremen.de/~hilboll/download/20120204.XD4_N2"; > localfile = "np_memmap.dat" > > import os > import urllib > > import numpy as np > > > # download data file > if not os.access(localfile, os.R_OK): > urllib.urlretrieve(url, localfile) > > with open(localfile, "r") as fd: > # read offset from first line of file > offset = int(fd.readlines()[0].split()[-2]) > # jump to begin of data block > fd.seek(offset) > # read until EOF > blob = fd.read() > print("Size of data blob [bytes]: {}".format(len(blob))) > print("This can actually be divided by 4: {} / 4.0 = {}".format( > len(blob), len(blob) / 4.0)) > # go back to begin of data block > fd.seek(offset) > print("But it cannot be loaded as np.memmap with dtype float32:") > np.memmap(fd, dtype="float32", mode="r") > > ---8<------- > > Any help is greatly appreciated :) > > -- Andreas. > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion >
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