Capitalise every other letter in a string in Python?

I’ve been trying to define a function that will capitalise every other letter and also take spaces into accout for example:

print function_name("Hello world") should print “HeLlO wOrLd” rather than “HeLlO WoRlD”

I hope this makes sense. Any help is appreciated.

Thanks, Oli

Answers:

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Method 1

def foo(s):
    ret = ""
    i = True  # capitalize
    for char in s:
        if i:
            ret += char.upper()
        else:
            ret += char.lower()
        if char != ' ':
            i = not i
    return ret

>>> print foo("hello world")
HeLlO wOrLd'

Method 2

I think this is one of those cases where a regular for-loop is the best idea:

>>> def f(s):
...     r = ''
...     b = True
...     for c in s:
...         r += c.upper() if b else c.lower()
...         if c.isalpha():
...             b = not b
...     return r
...
>>> f('Hello world')
'HeLlO wOrLd'

Method 3

Here is a version that uses regular expressions:

import re

def alternate_case(s):
    cap = [False]
    def repl(m):
        cap[0] = not cap[0]
        return m.group(0).upper() if cap[0] else m.group(0).lower()
    return re.sub(r'[A-Za-z]', repl, s)

Example:

>>> alternate_case('Hello world')
'HeLlO wOrLd'

Method 4

This should do the trick:

def function_name(input_string):
    should_capitalize = True
    chars = []
    for single_char in input_string:
        if not single_char.isalpha():
            chars.append(single_char)
            continue

        if should_capitalize:
            chars.append(single_char.upper())
        else:
            chars.append(single_char.lower())

        should_capitalize = not should_capitalize

    return ''.join(chars)

Method 5

A (hopefully elegant) recursive approach:

def funky_cap(s, use_lower=False):
    if s == '':
        return s
    elif not s[0].isalpha():
        return s[0] + funky_cap(s[1:], use_lower)
    elif use_lower:
        return s[0].lower() + funky_cap(s[1:], not use_lower)
    else: # when we need an uppercase letter
        return s[0].upper() + funky_cap(s[1:], not use_lower)

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0