Swap case of letters in string input parameter

Question

I would like to write a function in Python that takes a string which has lower and upper case letters as a parameter and converts upper case letters to lower case, and lower case letters to upper case.

For example:

>>> func('DDDddddd')
'dddDDDDD'

I want to do it with strings but I couldn't figure out how.

Solution 1

EDIT - Way simpler than my original answer, and supports both ASCII and unicode. Thanks commenters.

a = 'aBcD'
a.swapcase()
>> AbCd

Original answer - disregard

a = 'aBcD'
''.join(map(str.swapcase, a))
>> AbCd

This will map the str.swapcase() function to each element of the string a, swapping the case of each character and returning an list of characters.

''.join() will join each character in the list into a new string.

Solution 2

You should look into string.maketrans to create a translation table that could be used with str.translate. Other constants which will probably be useful are string.ascii_lowercase and string.ascii_uppercase.

Comments

[billwild]

i tried to do it with x.islower() or x.lower() but it print all uppercase or all lowercase. İ want to turn upper to lower, lower to upper

[mgilson]

@user1829771 -- you could do it that way too. You'd just need to build a list and then join it with str.join. e.g. ''.join(['a','b','c']) yields 'abc'

[Aesthete]

Yay learning is fun! I've learnt alot of python's subtleties from your answers @mgilson so I'm glad to pay it back.

[Steven Rumbalski]

Why work on individual characters? 'aBcD'.swapcase() is sufficient.

[Jon Clements]

If there's str.swapcase - why not just 'Ab'.swapcase() - d0h - beaten by Steve by 20 seconds :)?

[Aesthete]

Wow, what was I thinking. Thanks guys.