大文字小文字変換(capitalize, upper, lower)

capitalize()
upper()
lower()

str = 'this is a pen.'
 
str.capitalize()
'This is a pen.'
 
str = 'This is a pen.'
 
str.upper()
'THIS IS A PEN.'
 
str.lower()
'this is a pen.'

組み込み型 — Python 3.7.3 ドキュメント