On 01/05/2013 03:35 AM, Sia wrote:
I have strings such as:
>
> tA.-2AG.-2AG,-2ag
> or
> .+3ACG.+5CAACG.+3ACG.+3ACG
>
> The plus and minus signs are always followed by a number (say, i). I
want python to find each single plus or minus, remove the sign, the
number after it and remove i characters after that. So the two strings
above become:
>
> tA..,
> and
> ...
>
> How can I do that?
> Thanks.
I think it's a bit cleaner and nicer to do something similar to
itertools.takewhile but takewhile 'eats' a single next value.
I was actually doing some stuff that also needed this. I wonder if
there's a more elegant, robust way to do this?
Here's what I got for now:
class BIterator(object):
"""Iterator with 'buffered' takewhile."""
def __init__(self, seq):
self.seq = iter(seq)
self.buffer = []
self.end_marker = object()
self.last = None
def consume(self, n):
for _ in range(n): self.next()
def next(self):
val = self.buffer.pop() if self.buffer else next(self.seq,
self.end_marker)
self.last = val
return val
def takewhile(self, test):
lst = []
while True:
val = self.next()
if val is self.end_marker:
return lst
elif test(val):
lst.append(val)
else:
self.buffer.append(val)
return lst
def joined_takewhile(self, test):
return ''.join(self.takewhile(test))
def done(self):
return bool(self.last is self.end_marker)
s = ".+3ACG.+5CAACG.+3ACG.+3ACG"
not_plusminus = lambda x: x not in "+-"
isdigit = lambda x: x.isdigit()
def process(s):
lst = []
s = BIterator(s)
while True:
lst.extend(s.takewhile(not_plusminus))
if s.done(): break
s.next()
n = int(s.joined_takewhile(isdigit))
s.consume(n)
return ''.join(lst)
print(process(s))
Obviously it assumes the input is well-formed, but the logic would be
very easy to change to, for example, check for s.done() after each step.
- mitya
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