Python column manipulation in a text file.

I have an input file:

A03 58  0   0   0   -9
A03 59  0   0   0   -9
A03 60  0   0   0   -9
A03 61  0   0   0   -9
A03 62  0   0   0   -9
A03 63  0   0   0   -9
A03 64  0   0   0   -9
A03 65  0   0   0   -9
A03 66  0   0   0   -9
A03 67  0   0   0   -9
A03 68  0   0   0   -9
A03 69  0   0   0   -9
A03 70  0   0   0   -9
A03 71  0   0   0   -9
A03 72  0   0   0   -9
A03 73  0   0   0   -9
A03 74  0   0   0   -9

My wanted output:

A03_58 A03_58 0 0 0 -9
A03_59 A03_59 0 0 0 -9
A03_60 A03_60 0 0 0 -9 

The output will consider the second column in inputfile, add underscore to the first column and that letter. Then take that and copy it to the second column. I do know how to copy a column wit this:

# with open('inputfile.txt') as inputs:
#     for line in inputs:
#         parts = line.strip().split()
#         print("{0} {1}".format(parts[0], " ".join(parts)))

However, I need to change the column first and delete the second column before using above script.

I am not sure how to approach this after reading in the large input file. Browsed through some indexing questions, but can't find an answer.