Pairing the bases

A strand of DNA is a string of letters. You will write a function that gives the partner strand. Then you will count the hydrogen bonds between the two strands and the share of G and C in the strand.

The idea. In DNA, A pairs with T, and G pairs with C. An A-T pair has two hydrogen bonds and a G-C pair has three. A dictionary is a good way to hold the pairing rule.

Your tasks.

1. In partner, return the partner strand: the partner of each base, in order.
2. Set bonds to the number of hydrogen bonds between strand and its partner.
3. Set gc_percent to the per cent of the bases in strand that are G or C.