Regex - modifying python list

Question

I have a huge list in python that looks like this:

('foo','bar','foo/bar','foo1','bar/1')

Each value above demonstrates the character variety that the list contains - aplhanumeric plus slash. I need a way to turn that list into a list of tuples, like this:

(('foo','foo'),('bar','bar'),('foo/bar','foo/bar'),('foo1','foo1'),('bar/1','bar/1'))

So what better way to do this than Regex search and replace, right? (correct me if I'm wrong).

I am therefore trying to match anything between the quotes except for the commas, because technically, they are also between quotes. I used lookahead and lookbehind to match anything:

(?<=')(.*?)(?=')

But that only matches the values within the quotes and the commas. What I need is to match the value plus the quotes except the commas, and use a replacing regex to make the list look like the tuple above.

I can't do this by hand because the list is huge.

Any thoughts?

You say you have a huge list, then you show us a tuple, then you talk about parsing it with a regex, which implies that it's a str. Which is it? — abarnert
– abarnert, Commented Feb 21, 2013 at 20:07
Ok, let me clear it up. It is what you see. I need to convert the first to the second. It's a list of str but I need to convert it to a tuple of str — George K.
– George K., Commented Feb 21, 2013 at 20:08
Also, it seems like all you're trying to do is: tuple((element, element) for element in huge_list). Or, even more simple: tuple(zip(huge_list, huge_list)). Am I missing something? — abarnert
– abarnert, Commented Feb 21, 2013 at 20:08
And to convert a list to a tuple, you just call tuple. — abarnert
– abarnert, Commented Feb 21, 2013 at 20:09
@Robᵩ: It definitely isn't a duplicate of that meta question. And it isn't even really an instance of an XY question. The OP didn't ask "How can I fix this regex?", he asked how to his actual problem, then showed what he tried (the regex). Maybe he tried the wrong thing, but that doesn't make it a bad question. — abarnert
– abarnert, Commented Feb 21, 2013 at 22:18

abarnert · Accepted Answer · 2013-02-21 20:17:06Z

OK, you have a huge list of strings. You want a tuple, where for each element of the list, you have the pair (element, element).

That's exactly what zip does, except that it returns a list of such pairs in 2.x, or an iterator in 3.x. Either way, you can convert that to a tuple just by calling tuple. So:

tuple(zip(huge_list, huge_list))

More generally, if you want to transform a sequence element by element, you can use a comprehension or a generator expression. There are no "tuple comprehensions", but just passing a generator expression to the tuple function does the same thing. So:

tuple((element, element) for element in huge_list)

Or, if you wanted a tuple of (s[0], s[1:]) pairs instead of (s, s) pairs:

tuple((element[0], element[1:]) for element in huge_list)

And so on.

Meanwhile, I can't think of any situation where converting an object into its repr to run a regex transformation on it and re-parse it would be a good idea in Python. This isn't just a "Now they have two problems" issue; parsing the resulting string (and, even if you don't care about safety, figuring out how to deal with things where eval(repr(x)) != x) is going to be a harder problem than whatever you started with. So, if you ever spot yourself trying to make that work, take a step back.

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