Reading a file with Fortran formatted small floats, using numpy

问题

I am trying to read a data file written by a Fortran program, in which every once in a while there is a very small float like 0.3299880-104. The error message is:

>np.loadtxt(filename, usecols = (1,))

  File "/home/anaconda2/lib/python2.7/site-packages/numpy/lib/npyio.py", line 928, in loadtxt
    items = [conv(val) for (conv, val) in zip(converters, vals)]

  File "/home/anaconda2/lib/python2.7/site-packages/numpy/lib/npyio.py", line 659, in floatconv
    return float(x)

ValueError: invalid literal for float(): 0.3299880-104

Can I do something to make Numpy able to read this data file anyway?

回答1:

As @agentp mentioned in the comments, one approach would be to use the converters= argument to np.genfromtxt to insert the e characters before casting to float:

import numpy as np

# some example strings
strings = "0.3299880-104 0.3299880+104 0.3299880"

# create a "dummy file" (see http://stackoverflow.com/a/11970414/1461210)
try:
    from StringIO import StringIO     # Python2
    f = StringIO(strings)
except ImportError:
    from io import BytesIO            # Python3
    f = BytesIO(strings.encode())

c = lambda s: float(s.decode().replace('+', 'e').replace('-', 'e-'))

data = np.genfromtxt(f, converters=dict(zip(range(3), [c]*3)))

print(repr(data))
# array([  3.29988000e-105,   3.29988000e+103,   3.29988000e-001])

来源：https://stackoverflow.com/questions/34545060/reading-a-file-with-fortran-formatted-small-floats-using-numpy