Decapitalize string

Decapitalizes the first letter of a string.

• Use list slicing and str.lower() to decapitalize the first letter of the string.
• Use str.join() to combine the lowercase first letter with the rest of the characters.
• Omit the upper_rest parameter to keep the rest of the string intact, or set it to True to convert to uppercase.

def decapitalize(s, upper_rest = False):
  return ''.join([s[:1].lower(), (s[1:].upper() if upper_rest else s[1:])])

decapitalize('FooBar') # 'fooBar'
decapitalize('FooBar', True) # 'fOOBAR'