how to cut a string into a pair of strings in python

Question

What I want to do is:

mystr = i_return_a_string()
fst_part, snd_part = mystr[:4], mystr[4:]

But I'd be happier if this can be done (with a built-in function/method) like:

fst_part, snd_part = i_return_a_string().cut_at(4)

This is somewhat like str.partition, the difference is that I want to specify the index.

Is there a method for this?
if not, is what I have above the best way?

In this example, mystr is only needed as a temporal storage for the return value (of the function i_return_a_string), never to be referred again, which makes me a little uncomfortable.

Have you looked through the documentation of str methods? Try writing your own function then if you have problrms post another question. — wwii
– wwii, Commented Sep 13, 2014 at 14:58
Your solution using slicing - fst_part, snd_part = mystr[:4], mystr[4:] - is the idiomatic way to do this in Python. There's no cut_at string method or function built in (but you could write one if you liked). — Zero Piraeus
– Zero Piraeus, Commented Sep 13, 2014 at 14:58
What's against slicing? If you want to skip the temporary mystr you could make i_return_a_string() return a tuple of strings - that is do the slicing already inside the function. — Ghanima
– Ghanima, Commented Sep 13, 2014 at 15:00
@Yosh: Python names are just references; no need to be anxious about using them. :-) — Martijn Pieters
– Martijn Pieters, Commented Sep 13, 2014 at 15:02
@Yosh, no, there's nothing wrong with using a temporary variable if you need one ... and it's certainly better than jumping through hoops to avoid one. — Zero Piraeus
– Zero Piraeus, Commented Sep 13, 2014 at 15:03

Yosh · Accepted Answer · 2014-09-13 15:13:08Z

2

Summing up the comments given (as I don't dare leave this question open):

Using slicing is the idiomatic way (@ZeroPiraeus)
If I really don't like it, I could write my own function (@wwii, @ZeroPiraeus & @Bobby's answer) or I can change the base function so that it already returns a tuple(@Ghanima)
Using temporary variables are perfectly fine (@MartijnPieters, @ZeroPiraeus).
If I really, really, really needed to use built-in and blah, there's always another way (@myersjustinc 's answer).

answered Sep 13, 2014 at 15:13

Yosh

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Yosh Over a year ago

I intended this to be an answer, almost a complete one and certainly not just "additional information". These points listed above are basically what I needed to know. Q: Is there a method for this? -> A: No, but you can always write one. Q: Is what I have above the best way? -> A: Yes, and don't worry about mystr variable. I'm not getting why this is not considered to be an answer.

myersjustinc · Accepted Answer · 2014-09-13 15:08:49Z

1

If you really felt the need to (although I think it makes more sense to use mystr[:4], mystr[4:] instead as in your example), you could use regular expressions:

fst_part, snd_part = re.match(r'(.{4})(.*)', i_return_a_string()).groups()

edited Sep 13, 2014 at 15:08

answered Sep 13, 2014 at 15:02

myersjustinc

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myersjustinc Over a year ago

I agree it isn't a good solution, but it does what OP asked. It doesn't use an intermediate variable, it doesn't involve writing another function (because for whatever reason OP asked for a built-in), and it involves calling the i_return_a_string function only once.

Bobby · Accepted Answer · 2014-09-13 15:09:34Z

0

Might not be the exact syntax you're looking for, but maybe this is something up your alley?

def i_return_a_string():
    return "examplestring"

def cut_at(example_string, index):
    return example_string[:index], example_string[index:]

fst_part, snd_part = cut_at(i_return_a_string(), 4)
print fst_part, snd_part

answered Sep 13, 2014 at 15:09

Bobby

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2 Comments

Yosh Over a year ago

Yes, this is basically what I wanted. I wanted to know whether there's a default way to do that or not & whether I should write that function myself or use slicing.

Bobby Over a year ago

There's nothing really built-in. I'd say write your own function if you're going to use that functionality a lot. Your original syntax reminds me of Ruby syntax where you can easily chain methods.

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