Help with converting strings to arrays

[lwatson49]

I am trying to read in comma delimited data and build some numerical arrays.

# get a comma delimited string
row = ['10,20,40,50']
print (', '.join(row))
a = (','.join(row))
print (a[3])

This is returning 2 as the value of a[3}. I want it to return a numeric 40. How do create the numeric array from a common delimited string?

Thanks in advance,
Larry