import numpy

f = 'tmp.dat'

num_header_lines = 12

# Get header offset
with open(f) as fhr:
    for i in range(12): fhr.readline()
    offset = fhr.tell()

# Get data
# Next line gives:
# ValueError: Size of available data is not a multiple of data-type size.
# X = numpy.memmap(f, mode='r', dtype='f8', offset=offset) 

# This line gets bad data
X = numpy.memmap(f, mode='r', dtype='f8', offset=offset, shape=(40,))

print(X)