Randomly capitalize letters in string [duplicate]

Question

I want to randomly capitalize or lowercase each letter in a string. I'm new to working with strings in python, but I think because strings are immutable that I can't do the following:

i =0             
for c in sentence:
    case = random.randint(0,1)
    print("case = ", case)
    if case == 0:
        print("here0")
        sentence[i] = sentence[i].lower()
    else:
        print("here1")
        sentence[i] = sentence[i].upper()
    i += 1
print ("new sentence = ", sentence)

And get the error: TypeError: 'str' object does not support item assignment

But then how else could I do this?

Answer 1

You can use str.join with a generator expression like this:

from random import choice
sentence = 'Hello World'
print(''.join(choice((str.upper, str.lower))(c) for c in sentence))

Sample output:

heLlo WORLd

Answer 2

Build a new string.

Here's a solution with little changes to your original code:

>>> import random
>>> 
>>> def randomcase(s):
...:    result = ''
...:    for c in s:
...:        case = random.randint(0, 1)
...:        if case == 0:
...:            result += c.upper()
...:        else:
...:            result += c.lower()
...:    return result
...:
...:
>>> randomcase('Hello Stackoverflow!')
>>> 'hElLo StaCkoVERFLow!'

edit: deleted my oneliners because I like blhsing's better.