Python: Write two lists into two column text file

Question

Say I have two lists: a=[1,2,3] b=[4,5,6] I want to write them into a text file such that I obtain a two column text file:

Answer 1

A simple solution is to write columns of fixed-width text:

a=[1,2,3]
b=[4,5,6]

col_format = "{:<5}" * 2 + "\n"   # 2 left-justfied columns with 5 character width

with open("foo.csv", 'w') as of:
    for x in zip(a, b):
        of.write(col_format.format(*x))

Then cat foo.csv produces:

1    4    
2    5    
3    6    

The output is both human and machine readable, whereas tabs can generate messy looking output if the precision of the values varies along the column. It also avoids loading the separate csv and numpy libraries, but works with both lists and arrays.