fix: unable to import PyEVMBackend from fresh upgrade

[antazoey]

What was wrong?

fixes: #212

How was it fixed?

Check version when checking if py-evm installed

To-Do:

• Add entry to the CHANGELOG

Cute Animal Picture

[kclowes]

Thanks for the change, you're so fast! This is sort of a nit, but the error messaging where is_pyevm_available gets called assumes that pyevm isn't installed (like here, and here), so I wonder if it would be better to make these two separate checks? Like leave is_pyevm_available, and then add a method that checks that the version of py-evm is a high enough version so we can make the error messages slightly better. Or we can update the wording of the error messages. What do you think?

[antazoey]

here

I think what I would do then is change to the error messages to indicate pyevm >= 5.0.0 is not installed and maybe change the method name to is_supported_pyevm_version_available(). I think that would be easier because we will always have to check both anyway.

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Edit: I just pushed those changes but will think on this overnight as well!

[kclowes]

@unparalleled-js - This is ready to go, right?

[antazoey]

Yeah, unless you know a way to dynamically get the min supported version. I tried to see if we could do that but couldn't find a way.

[kclowes]

For this line/error messages? Is it set somewhere else?

[kclowes]

I felt bad for breaking your CHANGELOG again and again, so I added towncrier to eth-tester. So now there will be newsfragments like our other repos, and less merge conflicts 🎉. You can pull in master to get that update. I'm happy to add the snippet from the CHANGELOG in this PR to a newsfragment if you want, just let me know!

[antazoey]

I felt bad for breaking your CHANGELOG again and again, so I added towncrier to eth-tester. So now there will be newsfragments like our other repos, and less merge conflicts 🎉. You can pull in master to get that update. I'm happy to add the snippet from the CHANGELOG in this PR to a newsfragment if you want, just let me know!

I think I upgraded to the newsfragments approach correctly!