Well today I was forced with a rather simple task. I had to order a primer for a sub-cloning experiment that was the reverse primer corresponding to the last twenty bases of a given protein coding gene sequence.

Here is how python made the task super easy

1) First I opened the pubmed page with my sequence and copied the forward strand to my interactive python session

2) Then I wrote a couple of  lines to generate the reverse complement at the same time reversing the order of the string

So in the above example the

Is the reverse complement dictionary. The for loop replaces each nucleotide with its complement and simultaneously reverses the order , because every nucleotide is added to the begining ( i.e prepended) . So the last nucleotide ends up first.

The other way to do the same thing would be to use python string reversal as demonstrated in the code below

The cool part here is the funky and admittedly unreadable string-reversal syntax,

[python] reverse_5prime_3prime = p[::-1]
[/python]

So In python string reversal is powerful. The p[::-1] basically says , give me the string from start to finish in backwards order (-1) . This elegant string reversal in python is explained well in this post and gives us the primer sequence in the correct 5-prime to 3-prime order as required by the oligo-synthesizing order forms.