I have a string which contains a fixed character. Can I generate a permutation of strings by replacing it with another character or string?? Say, I have something like this:
designatedstring="u"
replacerstring="ough"
s="thruput"
I want an output like:
l=["throughput","thrupought","throughpought"]
Is there any way to do this?
More itertools sugar:
>>> parts = s.split(designatedstring)
>>> num = len(parts) - 1
>>> replacements = itertools.product([designatedstring, replacerstring], repeat=num)
>>> replacements = list(replacements)
>>> replacements.remove((designatedstring,) * num)
>>> for r in replacements:
... print ''.join(itertools.chain(*zip(parts, r + ('',))))
...
thrupought
throughput
throughpought
If you can bear with original string in the result, you can omit ugly transformations on 4 and 5 lines.
Here's an interesting way to do it, though I'd still go with the itertools solution.
Notice that the list of strings you produce is morally a binary tree: at each instance of the replacement character in the string you either want to ignore it ("go left") or replace it ("go right"). So you can make a binary tree structure out of the replacement strings. Walking the leaves of a binary tree is easy.
class ReplacementTree(object):
def __init__(self, s, src, target, prefix=""):
self.leaf = src not in s
if 1 == len(s.split(src, 1)):
self.head, self.tail = s, ""
else:
self.head, self.tail = s.split(src, 1)
self.prefix, self.src, self.target = prefix, src, target
@property
def value(self):
if self.leaf:
return self.prefix + self.head
@property
def left(self):
if self.leaf:
return None
else:
return ReplacementTree(self.tail,
self.src,
self.target,
prefix=self.prefix + self.head + self.src)
@property
def right(self):
if self.leaf:
return None
else:
return ReplacementTree(self.tail,
self.src,
self.target,
prefix=self.prefix + self.head + self.target)
def leaves(tree):
if tree.leaf:
yield tree.value
else:
for leaf in leaves(tree.left):
yield leaf
for leaf in leaves(tree.right):
yield leaf
Example:
>>> x = repltree.ReplacementTree("thruput", "u", "ough")
>>> list(repltree.leaves(x))
['thruput', 'thrupought', 'throughput', 'throughpought']
From the input given in your question, this will produce the list requested:
s="thruput"
designatedstring="u"
replacerstring="ough"
l = []
for i in range(len(s)):
if s[i] == designatedstring:
l += [s[:i] + replacerstring + s[i + 1:]]
l += [s.replace(designatedstring, replacerstring)]
'toughtoughtu', 'toughtutough' and 'tutoughtough'. Which technically wasn't specified in the question. ;)