GC content

# get the fraction of GC content of a DNA sequence in percent

>>>> from Bio.SeqUtils import GC

>>>> GC("TGCAA")

40.0

http://biopython.org/DIST/docs/api/Bio.SeqUtils-pysrc.html#GC

# without Biopython

http://saml.rilspace.org/calculating-gc-content-in-python-and-d-how-to-get-10x-speedup-in-d