Python 3 regression: Undefined Jinja2 variables get rendered as empty string in linting

[zklaus]

Solution to issue cannot be found in the documentation.

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Issue

For linting, undefined Jinja2 variables get rendered by conda_smithy.utils.NullUndefined. That class contains a __unicode__ method that returns the name of the variable. This is useful to put a clear placeholder where variables will be filled by variants from conda_build_config.yaml during the actual build. However, NullUndefined doesn't overwrite the __str__ method of Jinja's own Undefined, which returns an empty string.

In effect, linting in a Python 2 environment renders, e.g. - {{ libjpeg }} as - libjpeg, but in a Python 3 environment, we get - which becomes None in the requirements_section dictionary.

Installed packages

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Environment info

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