python字符串的查找：
mystr = "hello world and itcast and itheima and Python"
# 1. find()
# print(mystr.find('and')) # 12
# print(mystr.find('and', 15, 30)) # 23
# print(mystr.find('ands')) # -1 , ands子串不存在
python字符串的查找：
# 2.index()
# print(mystr.index('and')) # 12
# print(mystr.index('and', 15, 30)) # 23
# print(mystr.index('ands')) # 如果index查找子串不存在，报错
# 3.count()
# print(mystr.count('and', 15, 30))
# print(mystr.count('and')) # 3
# print(mystr.count('ands')) # 0
# 4.rfind()
# print(mystr.rfind('and')) #最后一个and的首位置
# print(mystr.rfind('ands'))
# 5.rindex()
# print(mystr.rindex('and')) #最后一个and的首位置
# print(mystr.rindex('ands'))
