According to the PEP 8 coding style guidelines, how should constant values be named in Python?

1.  in camel case without using underscores to separate words — e.g. maxValue = 255
2.  in lowercase with underscores to separate words — e.g. max_value = 255
3.  in all caps with underscores separating words — e.g. MAX_VALUE = 255
4.  in mixed case without using underscores to separate words — e.g. MaxValue = 255

Correct Answer:

•  in all caps with underscores separating words — e.g. MAX_VALUE = 255