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I would like this added to the documentation.

@vstinner may I ask you to review this PR?

Thanks for the PR, but this feels like an implementation detail. Would you mind talking more about the use case you have for the exact set of characters used to be a documented guarantee?

@hauntsaninja I don't exactly want a guarantee or whatnot. At the time of creating this PR, I want to know what the tempfile's randomly generated names would look like, and for my use case at the time, I wanted to generate my own files ensuring I would confuse them for the tempfile's random names. So I decided to look at the source code to see what kind of characters would be used to create the tempfiles, so I decided to document it so that others who had the same inquiry as me would know.

Okay, thanks, that helps me better understand the use case. I think the right way to disambiguate temporary files from other files is to use the prefix and suffix arguments. I'd much rather encourage users to use those arguments than e.g. rely on the fact that the implementation doesn't currently use a certain character in filenames.

Putting statements in the documentation is essentially a guarantee. I appreciate your intention to save time for others, but curiosity about implementation details is still best served by looking at the implementation (one of my favourite things about Python is that the standard library is quite readable).