源码解释：

"""A collection of string constants.

Public module variables:

whitespace -- a string containing all ASCII whitespace
ascii_lowercase -- a string containing all ASCII lowercase letters
ascii_uppercase -- a string containing all ASCII uppercase letters
ascii_letters -- a string containing all ASCII letters
digits -- a string containing all ASCII decimal digits
hexdigits -- a string containing all ASCII hexadecimal digits
octdigits -- a string containing all ASCII octal digits
punctuation -- a string containing all ASCII punctuation characters
printable -- a string containing all ASCII characters considered printable

"""

示例代码：

import string

aa = string.ascii_letters
print(aa)

bb = string.ascii_lowercase
print(bb)

cc = string.ascii_uppercase
print(cc)

dd = string.hexdigits
print(dd)

ee = string.printable
print(ee)

运行结果：

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