小写→大写，大写→小写，只保留首字母大写的三种方法

小写→大写

list1 = ['wo','ai','ni','zhong', 'guo']
SRT_list = []
for x in list1:SRT_list.append(x.upper()) # ['WO', 'AI', 'NI', 'ZHONG', 'GUO']

大写→小写

list3 = ['WO', 'AI', 'NI', 'ZHONG', 'GUO']
List = []
for j in list3:List.append(j.lower()) # ['wo', 'ai', 'ni', 'zhong', 'guo']

 只保留首字母大写

list2 = ['WO', 'AI', 'NI', 'ZHONG', 'GUO']
LIST = []
for i in list2:LIST.append(i.title()) #['Wo', 'Ai', 'Ni', 'Zhong', 'Guo']