Folllow up: Support for python "re" module for doing regex in jinja templates

[hochoy]

resolves #1755

This is a follow-up PR for the same exact feature posted by @whisperstream at #1755 . Descriptions below will almost exactly match. My first attempt at contributing to dbt 😄 ! Please do not hesitate to point out any possible improvements.

Description

Describe the feature
"I have a case where I'd like to be able to do a regex in a jinja template for matching a particular set of values. It would be handier to have a access to python's re module than having to use normal string manipulation and matching" ~ @whisperstream

Describe alternatives you've considered
Similar to the original issue, I have used the following to work around not having RegEx

1. for loops
2. string replacement and splitting + array indexing
3. IF and NOT statements

Additional context
"This change is not database specific, it would apply to all jinja templates in the same way that datetime and pytz modules are made available" ~ @whisperstream

Additionally, I checked the list of exported functions from the native python re module and they do not introduce any unsafe behaviour with respect to database connections, exposed secrets, etc:
https://github.com/python/cpython/blob/83c86cf54b36a7325f615f5adf22b28e48f0e72d/Lib/re.py#L135-L141

__all__ = [
    "match", "fullmatch", "search", "sub", "subn", "split",
    "findall", "finditer", "compile", "purge", "template", "escape",
    "error", "Pattern", "Match", "A", "I", "L", "M", "S", "X", "U",
    "ASCII", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
    "UNICODE",
]

If there is a concern that future versions of re will introduce unsafe behaviour, I can close this and create another PR with explicit re imports instead of __all__.

Who will this benefit?
"Anybody who wants to do more complex string manipulation and string checking in a more straight-forward way than is possible today" ~ @whisperstream

For us, this comes up often when an input array of strings to a macro is "dirty" and the strings need to be cleaned/filtered via RegEx. Another case if we are looking for certain string occurrences that might decide the logical IF, ELSE flow of our macros.

Checklist

• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt next" section.

[hochoy]

First time contributing a PR! Assuming this is accepted, if I push a commit for the Changelog and dbt next sections, how do I re-trigger the circleci tests? Does the test re-run on commit or should I create a new PR? Thanks!

[jtcohen6]

Thanks for this PR, @hochoy, and the detailed description! I'm totally in favor of pulling in regex functionality to the Jinja layer. It's also a great help during dbt development, even if we end up rewriting the trickiest bits in python.

Assuming this is accepted, if I push a commit for the Changelog and dbt next sections, how do I re-trigger the circleci tests?

Any commit you add to this open PR will automatically re-trigger the Circle CI tests.

@drewbanin Do you have any concerns about pulling in re.__all__? I'm remembering Jake's comment from #1997, where we discussed wanting explicit yeslists:

I agree that lots of re should be available (search, match, findall, sub, and the constants seems like the minimum)

I think that's most of what we'd want, anyway, but I also don't have specific reasons to oppose the rest.

[drewbanin]

I think adding the entire regex module is probably appropriate - @iktl any opposition on your end? Thanks for opening this PR @hochoy!

[iktl]

I think adding the entire regex module is probably appropriate - @iktl any opposition on your end? Thanks for opening this PR @hochoy!

I don't see any reason not to 👍 — no opposition here

[hochoy]

Thank you for the feedback! I hope this will speed up the (already fast) workflow for all dbt devs.

[jtcohen6]

Thanks for the contribution @hochoy!

[kdutta-c]

Do I have to install this as a package? If so, can you tell me how?

[dataders]

Maybe there's a doc out there somewhere, but I'm also confused as to how to use the regex functions inside of dbt-jinja. I wrote a SO question that I'll answer myself once I find out.

[jtcohen6]

No need to install additional packages. You can access methods from modules.re right in the Jinja context, such as match:

https://docs.getdbt.com/reference/dbt-jinja-functions/modules#re

[kdutta-c]

dbt comes with re. I may have overthought about this because in Python we import re
I did something like this
{% set date_format = '^(\d{4}\-\d{2}\-\d{2})' %}
and then...
{% set date_check = modules.re.match(date_format,blb, modules.re.IGNORECASE) %}

[dataders]

You can access methods from modules.re

beautiful thanks! for reference I was trying to filter an Agate table as given in the Agate cookbook this:

new_table = table.where(lambda row: re.match('^C', str(row['state'])))