altura = np.loadtxt("bio.dat",delimiter=',',usecols=(5,),dtype='float')
  File "/usr/lib/python2.7/dist-packages/numpy/lib/npyio.py", line 846, in loadtxt
    vals = [vals[i] for i in usecols]
IndexError: list index out of range

import numpy as np

altura = np.loadtxt("bio.dat",delimiter=',',usecols=(5,),dtype='str')
print altura

1 Katherine Oquendo M 18    1.50    50
2 Pablo Restrepo    H 20    1.83    79
3 Ana Agudelo   M 18    1.58    45
4 Kevin Vargas  H 20    1.74    80
5 Pablo madrid  H 20    1.70    55

x=sum(altura)

import csv

txt_file = r"mytxt.txt"
csv_file = r"mycsv.csv"

# use 'with' if the program isn't going to immediately terminate
# so you don't leave files open
# the 'b' is necessary on Windows
# it prevents x1a, Ctrl-z, from ending the stream prematurely
# and also stops Python converting to / from different line terminators
# On other platforms, it has no effect
in_txt = csv.reader(open(txt_file, "rb"), delimiter = 't')
out_csv = csv.writer(open(csv_file, 'wb'))

out_csv.writerows(in_txt)

In [17]: from StringIO import StringIO
In [18]: s="""
1 Katherine Oquendo M 18    1.50    50
2 Pablo Restrepo    H 20    1.83    79
3 Ana Agudelo   M 18    1.58    45
4 Kevin Vargas  H 20    1.74    80
5 Pablo madrid  H 20    1.70    55
"""
In [19]: S=StringIO(s)
In [20]: data=np.loadtxt(S,dtype=float,usecols=(5,))
In [21]: data
Out[21]: array([ 1.5 ,  1.83,  1.58,  1.74,  1.7 ])
In [22]: np.sum(data)
Out[22]: 8.3499999999999996

import numpy as np
fname = 'stack25828405.txt'
data=np.loadtxt(fname,dtype=float,usecols=(5,))
print data
print np.sum(data)

2119:~/mypy$ python2.7 stack25828405.py
[ 1.5   1.83  1.58  1.74  1.7 ]
8.35

altura = np.loadtxt("bio.dat",delimiter=',',usecols=(5,),dtype=‘str’,comments='')