Reimplementing numpy.genfromtxt in Fortran for Python
Numpy's genfromtxt is indeed slow which is due to it's flexibility. It tries very hard to figure out what the layout of your data file is. So you will not get this flexibility by implementing it yourself in fortran.

Have you tried using loadtxt instead?

Depending on the conditions, for the same matrix genfromtxt may be more than 20 times slower than loadtxt.

BTW a simple implementation in python which is in my case faster than both loadtxt and genfromtxt:

with open("matrix.txt",'r') as f:
    a=array([fromstring(s,dtype=float,sep=' ') for line in f])


I guess the speed comes from the fact that I do not have to read in the whole file to check how many lines it has.

EDIT: I realise this does not really answer your question, but I believe that the speed-up that you may get from using fortran does not really warrant the loss of flexibility.