**使用之前:
import string;
可方便使用模块内的纯字母（包含大小写），纯小写字母，纯大写字母，纯数字，16进制数字,全部纯标点符号，全部字母符号**
The constants defined in this module are:
string.ascii_letters
The concatenation of the ascii_lowercase and ascii_uppercase constants described below. This value is not locale-dependent.
string.ascii_lowercase
The lowercase letters ‘abcdefghijklmnopqrstuvwxyz’. This value is not locale-dependent and will not change.
string.ascii_uppercase
The uppercase letters ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ’. This value is not locale-dependent and will not change.
string.digits
The string ‘0123456789’.
string.hexdigits
The string ‘0123456789abcdefABCDEF’.
string.letters
The concatenation of the strings lowercase and uppercase described below. The specific value is locale-dependent, and will be updated when locale.setlocale() is called.
string.lowercase
A string containing all the characters that are considered lowercase letters. On most systems this is the string ‘abcdefghijklmnopqrstuvwxyz’. The specific value is locale-dependent, and will be updated when locale.setlocale() is called.
string.octdigits
The string ‘01234567’.
string.punctuation
String of ASCII characters which are considered punctuation characters in the C locale.
string.printable
String of characters which are considered printable. This is a combination of digits, letters, punctuation, and whitespace.
string.uppercase
A string containing all the characters that are considered uppercase letters. On most systems this is the string ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ’. The specific value is locale-dependent, and will be updated when locale.setlocale() is called.
string.whitespace
A string containing all characters that are considered whitespace. On most systems this includes the characters space, tab, linefeed, return, formfeed, and vertical tab.