1. "" , ”, """ """
2.Strings are stored as sequences of characters indexed by integers, starting at zero.
3.To extract a substring, use the slicing operator s[i:j].
4.Strings are concatenated with the plus (+) operator: g = a + " This is a test"
5.To perform mathematical calculations, strings first have to be converted into a numeric value using a function such as int() or float(). For example: z = int(x) + int(y) # z = 79 (Integer +)
6.Non-string values can be converted into a string representation by using the str(), repr(), or format() function.
，告诉自己，我这次失败了，
