feat: add __repr__ methods for FluxTable, FluxColumn, FluxRecord

[takluyver]

Proposed Changes

__repr__ methods are a convenient feature for exploring objects interactively - i.e. in an interactive shell or a Jupyter notebook. The default representation of an object basically just identifies the type:

<influxdb_client.client.flux_table.FluxRecord at 0x7f5720b63460>

By defining __repr__, objects can display themselves with more useful information:

<FluxTable: 11 columns, 360 records>
FluxColumn(7, label='_measurement', data_type='string', group=True, default_value='')
<FluxRecord field=counter value=282.0>

There are loose conventions for how reprs are formatted, though I'm not aware of any reference for them. They generally fit on one line, to simplify formatting in containers. If it's practical to fit in all the information to reconstruct the object, the repr should be a code snippet to construct it (as I've done with FluxColumn). If not, the repr usually looks like <ClassName detail>, with whatever details are most likely to convey useful information. I've had a guess at what might be useful for FluxTable & FluxRecord, but I'm happy to revise them.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• pytest tests completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[takluyver]

Oh, there is a reference for the convention I described, in the Python docs:

If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form <...some useful description...> should be returned.
...
This is typically used for debugging, so it is important that the representation is information-rich and unambiguous.

[bednar]

Thanks for your PR 👍

There is a few requirements that should be satisfy before we accept the PR:

[takluyver]

Thanks!

I was trying to ensure that the reprs fit on a single line (of reasonable length), by showing just a summary of the information, rather than the full contents. This isn't strictly required - e.g. pandas objects use multi-line reprs effectively - but I generally consider it good practice. In particular, if you get a list of FluxTables, which seems quite common, it's easier to see if each one sits on a single line.

[bednar]

@takluyver, thank you for the explanation, it sounds reasonable. Only two requirements remains:

[bednar]

Thanks again for your PR 👍, we are ready to merge into master.