An option to ignore unknown variables

[Efrain]

Hi

Nice project BTW...

I suggest to add an option in the command line to ignore when there is a undefined variable on the template, so this type of error won't occurs

jinja2.exceptions.UndefinedError: 'MY_UNKNOWN_VAR' is undefined

I think this will be helpful when you have multiple variable inputs for the same template, so I can execute things like.

j2 --ignore_unknown my_template.j2 input1.yaml | j2 --ignore_unknown my_template.j2 input2.yaml | j2 my_template.j2 input3.yaml

Regards

[Andreas Bollig]

Hi there,

thanks for implementing this!

I found two problems, though. Maybe the issue can be reopened?

1. The undefined flag doesn't ignore unknown nested parameters. For instance {{ i }} is successfully ignored if "i" is undefined but {{ a.t }} throughs an exception if "a" is undefined.

2. The current implementation replaces unknown parameters with the empty string. This means that 3fr61n's example of piping multiple invocations of j2 won't work. I think it would be great if unknown parameters would stay in the file, i.e. if "i" is undefined, invoking j2 would replace {{ i }} with {{ i }}, so that later jinja2 runs can replace the remaining parameters.

BR Andreas

[Mark]

@akbo, the idea of keeping unknown variables "as is" may have its use, but in most cases will only lead to errors.

Suppose you've messed up your environment, and a variable that was previously available is now not set. Then j2cli will not report any errors, and happily produce a file that is actually malformed. This behaviour does not seem correct to me.

In case you want to use multiple data sources (input1.yaml, input2.yaml), it's best to merge them. In most cases, simple cat input1.yaml input2.yaml >> input_merged.yaml will work just fine.
You can also pump them right into j2cli:

cat input1.yaml  input2.yaml | j2cli --format=yaml template.j2

Kind regards,
Mark

[Andreas Bollig]

Hey Mark,

I understand. Thanks for the explanation.

How about my first point?

BR Andreas

[Mark]

Hey @akbo , I'm sorry I forgot about # 1 :)
This actually is Jinja2 behavior: it can ignore undefined top-level variables, but can't ignore accessing missing keys.

[Andreas Bollig]

Alright, thanks for looking into it.

For my specific use case I found the following workaround (might be interesting for other people having the same issue I have): Jinja2 ignores everything between {% raw %} and {% endraw %}. So we can put this around everything that we need to stay as is in the template.