Need help understanding this python error return (Google search doesn't help)

In python code. When you see a negative in front开发者_JAVA技巧 of a Error Flag, what does it mean?

return -errno.EACCES

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That's a C style error return. A practice that is popular is to return a meaningful non-negative result of the function on success or a negative error code on failure.

In this case, the error EACCES means that permision was denied.

(See also this question)

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It means negation. errno.EACCES (permission denied) is the number 13 (positive). The author of that code had a convention where he wanted the error number to be negative to be interpreted by their code later.

Presumably, he has a reason for adopting this convention. E.g., the function returns non-negative integers on non-errors that are used later on in the program.

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The author may has restricted error code to negative value in order to be able to return various (positive) success values.

The convention seems to be used by some people:
http://www.google.com/codesearch?hl=en&lr=&q=%22return+-errno%22+lang%3Apython&sbtn=Search