Fix for Issue#518

[daminichopra]

Proposed changes

Inserted a start check to verify that crate back off factor

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• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

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Further comments

Fix for Issue

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[daminichopra]

@chicco785 Gentle Reminder for merging!!

[c0c0n3]

hi @daminichopra, thanks for this. I've just looked at the crate docs

• https://crate.io/docs/python/en/latest/connect.html#backoff-factor

where they explicitly mention the backoff factor should be between 0 and 120. So we need to output a config error not a warning. I suggest we change this PR as follows:

1. Implement a new config reader for float ranges, e.g. class FloatRangeVar(Evar) ...
   • FloatRangeVar gets instantiated with an interval [a b] where config values are expected to be, e.g. [0, 120] in your case.
   • on reading a config value x, FloatRangeVar raises a ValueError if x is not in [a, b].
2. Simply use this new config reader in the translator, e.g. backoff_factor = ... .read(FloatRangeVar('CRATE_BACKOFF_FACTOR', 0.0, 0, 120))

This way we get to reuse the validation code in the future if we have similar env vars. What do you think? Does it make any sense?