substitution

[Iain King]

On Jan 18, 12:41 pm, Iain King <iaink... at gmail.com> wrote:
> On Jan 18, 10:21 am, superpollo <ute... at esempio.net> wrote:
>
>
>
> > superpollo ha scritto:
>
> > > hi.
>
> > > what is the most pythonic way to substitute substrings?
>
> > > eg: i want to apply:
>
> > > foo --> bar
> > > baz --> quux
> > > quuux --> foo
>
> > > so that:
>
> > > fooxxxbazyyyquuux --> barxxxquuxyyyfoo
>
> > > bye
>
> > i explain better:
>
> > say the subs are:
>
> > quuux --> foo
> > foo --> bar
> > baz --> quux
>
> > then i cannot apply the subs in sequence (say, .replace() in a loop),
> > otherwise:
>
> > fooxxxbazyyyquuux --> fooxxxbazyyyfoo --> barxxxbazyyybar -->
> > barxxxquuxyyybar
>
> > not as intended...
>
> Not sure if it's the most pythonic, but I'd probably do it like this:
>
> def token_replace(string, subs):
>         subs = dict(subs)
>         tokens = {}
>         for i, sub in enumerate(subs):
>                 tokens[sub] = i
>                 tokens[i] = sub
>         current = [string]
>         for sub in subs:
>                 new = []
>                 for piece in current:
>                         if type(piece) == str:
>                                 chunks = piece.split(sub)
>                                 new.append(chunks[0])
>                                 for chunk in chunks[1:]:
>                                         new.append(tokens[sub])
>                                         new.append(chunk)
>                         else:
>                                 new.append(piece)
>                 current = new
>         output = []
>         for piece in current:
>                 if type(piece) == str:
>                         output.append(piece)
>                 else:
>                         output.append(subs[tokens[piece]])
>         return ''.join(output)
>
> >>> token_replace("fooxxxbazyyyquuux", [("quuux", "foo"), ("foo", "bar"), ("baz", "quux")])
>
> 'barxxxquuxyyyfoo'
>
> I'm sure someone could whittle that down to a handful of list comps...
> Iain

Slightly better (lets you have overlapping search strings, used in the
order they are fed in):

def token_replace(string, subs):
	tokens = {}
	if type(subs) == dict:
		for i, sub in enumerate(subs):
			tokens[sub] = i
			tokens[i] = subs[sub]
	else:
		s = []
		for i, (k,v) in enumerate(subs):
			tokens[k] = i
			tokens[i] = v
			s.append(k)
		subs = s
	current = [string]
	for sub in subs:
		new = []
		for piece in current:
			if type(piece) == str:
				chunks = piece.split(sub)
				new.append(chunks[0])
				for chunk in chunks[1:]:
					new.append(tokens[sub])
					new.append(chunk)
			else:
				new.append(piece)
		current = new
	output = []
	for piece in current:
		if type(piece) == str:
			output.append(piece)
		else:
			output.append(tokens[piece])
	return ''.join(output)