数学计算
要利用相关的数学计算函数，首先需要把数学模块包含进来：
进行计算：
随机数
包含随机函数:
Python also includes more exotic numeric objects—such as complex, fixed-precision, and rational numbers, as well as sets and Booleans—and the third-party open source extension domain has even more (e.g., matrixes and vectors, and extended precision numbers). We’ll defer discussion of these types until later in this chapter and book.
So far, we’ve been using Python much like a simple calculator; to do better justice to its built-in types, let’s move on to explore strings.
String
注意：
In Python, we can also index backward, from the end—positive indexes count from the left, and negative indexes count back from the right:
File Operation: