finding homopolymers in both directions

[Lee Sander]

Hi,
Suppose I have a string such as this
'aabccccccefggggghiiijkr'

I would like to print out all the positions that are flanked by a run
of symbols.
So for example, I would like to the output for the above input as
follows:

2  b  1 aa
2  b  -1 cccccc
10  e  -1 cccccc
11  f  1 ggggg
17 h  1 iii
17 h -1 ggggg

where the first column is the position of interest, the next column is
the entry at that position,
1 if the following column refers to a runs that come after and -1 if
the runs come before

I can do this easily for forward (shown below) but not clear how to do
this
backwards.

I would really appreciate it if someone can help with this problem.

I feel like a regex solution would be possible but I am not too good
with regex.

The code for forward is as follows:

def homopolymericSites(Seq):
		Seq=Seq.upper()
		i=0
		len_seq=len(Seq)-1# hack to prevent boundary condition
		while i < len_seq:
			bi=Seq[i]
			k=1
			# go to the start of a homopolymer
			while 1:
				if i+k >= len_seq: break # no more sequence left
				if bi==Seq[i+k]:
					k+=1
				else:
					break
			if k>1: # homopolymer length
				i=i+k
				id_of_chr_which_proceeds_homopolymer=Seq[i] # note not i+1
				pos_of_chr_which_proceeds_homopolymer=i+1	# +1 to convert it to 1-
index notation
				id_of_homopolymer=Seq[i-1]
				length_of_homopolymer=k

				print "%s\t%s/%s\t%s" %(pos_of_chr_which_proceeds_homopolymer,
id_of_chr_which_proceeds_homopolymer, id_of_homopolymer,
											length_of_homopolymer)
			else:
				i+=1