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.
原文：http://blog.csdn.net/jiandanjinxin/article/details/43758739