How do I sort a string in alphabetical order in Python?

Question

I know there is a sort function:

>>> a = 'bags'
>>> ''.join(sorted(a))
'abgs'

However, I need to write mine from scratch. I think I would like to use mergesort but I'm not sure how that would work for a string in Python. E.g., can I compare characters? Can I find the middle of a string somehow?

I'm using Python 3.4.

Strings are just immutable sequences; but make your string a list with a_list = list(a) and go from there instead. — Martijn Pieters
– Martijn Pieters, Commented Mar 22, 2014 at 20:54
Will I not be able to sort the string (e.g. with this method stackoverflow.com/questions/18761766/mergesort-python) if I keep is as a string? Should I do string-->list-->sort-->string? — Michi
– Michi, Commented Mar 22, 2014 at 21:01
That question doesn't modify the result in-place, you can just pass the string directly to that function. Like sorted(), it'll return a list though. — Martijn Pieters
– Martijn Pieters, Commented Mar 22, 2014 at 21:02
I need it to be a string, though, so that I could use it to initialize my object. I just need to use the .join function, correct? — Michi
– Michi, Commented Mar 22, 2014 at 21:08
Yes, a list of strings can be joined with ''.join(list_of_strings). — Martijn Pieters
– Martijn Pieters, Commented Mar 22, 2014 at 21:10

mattgathu · Accepted Answer · 2014-03-22 20:57:18Z

1

Yes you could compare characters.

b > a evaluates to True in Python, and so forth.

You could first convert the string to a list, and get it's middle via its length, do sequential comparison and then join the sorted list to get back a sorted string.

answered Mar 22, 2014 at 20:57

mattgathu

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2 Comments

Michi Over a year ago

Perfect, I think that's all I need. I think I'll use something like this mergesort but for my string: stackoverflow.com/questions/18761766/mergesort-python

mattgathu Over a year ago

great..and you can also define the lists append outside the for loops for optimization. check:wiki.python.org/moin/PythonSpeed/PerformanceTips#Avoiding_dots...

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