|
# demonstrates
#
# - list comprehension
# - method fromkeys
# - sequence unpacking
# - method iteritems
# - gradually building complex string
def dinucleotide_distribution(s):
"""Return histogram of dinucleotide
distribution in DNA string s"""
nuc = "A", "C", "G", "T"
keys = [ (a, b) for a in nuc for b in nuc]
# create dictionary where all dinucleotide keys
# have default value 0:
d = dict.fromkeys( keys, 0 )
for i in xrange(0, len(s)-1):
d[(s[i], s[i+1])] += 1
# build histogram string as a list first:
histogram = []
for (n1, n2), m in sorted(d.iteritems()):
if m>0:
histogram.append("%s%s : %3d"%(n1, n2, m))
# turn list into string:
return "\n".join(histogram)
s = raw_input("Input DNA string: ")
print dinucleotide_distribution(s.upper())
|
