I have a list where each element is a letter. Like this:
myList = ['L', 'H', 'V', 'M']
However, I want to reverse these letters and store them as a string. Like this:
myString = 'MVHL'
is there an easy way to do this in python? is there a .reverse I could call on my list and then just loop through and add items to my string?
There is a reversed() function, as well as the [::-1] negative-stride slice:
>>> myList = ['L', 'H', 'V', 'M']
>>> ''.join(reversed(myList))
'MVHL'
>>> ''.join(myList[::-1])
'MVHL'
Both get the job done admirably when combined with the str.join() method, but of the two, the negative stride slice is the faster method:
>>> import timeit
>>> timeit.timeit("''.join(reversed(myList))", 'from __main__ import myList')
1.4639930725097656
>>> timeit.timeit("''.join(myList[::-1])", 'from __main__ import myList')
0.4923250675201416
This is because str.join() really wants a list, to pass over the strings in the input list twice (once for allocating space, the second time for copying the character data), and a negative slice returns a list directly, while reversed() returns an iterator instead.
You can use reversed (or [::-1]) and str.join:
>>> myList = ['L', 'H', 'V', 'M']
>>> "".join(reversed(myList))
'MVHL'
