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Scraper Things

Most of the week was spent rewriting the Scraper functions to go with the new parse-pattern and then looking for edge cases in the new implementations, fixing bugs and updating tests.

{{Catching up}}

In the scraper, while trying to merge baseurl (an strftime formatted pattern i.e. %Y%m etc) and pattern (parse formatted pattern i.e. {year:4d}{month:2d} etc), I faced two choices, we could either:

  • Make the input all parse-style formatted. generate the datetime-compatible string from here wherever it is required, however the problem i was running into here is parse-stuff like {year:2d} will collide with {instrument} like placeholders on which we mean to call .format(**kwargs) on. All the ways I could think of pulling it off included adding a large no. of lines of code in the really early part of __init__().

  • Make the input all datetime formatted and generate the parse pattern from here. The problem with this is there are edge-cases when sometimes users define variables like {Level:1d} which we have no way of knowing beforehand. One way to go about this could’ve been that we tell the user to define a pattern string in addition to baseurl whenever they have any new variables like that.

We ended up going with the first. My mentor, Nabil introduced me to how there’s a prevalence of using double-curly brackets in places where we need to escape / use them with single curly brackets, and sure enough, the parse module supports that. So that took care of the problem there, I was mostly a bit concerned that I’ll have to go back to the second way even though I had started with it before pivoting to the first one.


Nabil pointed out that we weren’t being very good at communicating and that has a negative effect on the project which lead me to change how I was approaching it.

A lot of times I was debugging things by including print statements here and there, and since my project now involves changing API it had me updating tests and a lot of these times the problem would just be in my understanding on how to convert the patterns and just how the new input should look like. Previously, I would only send a message on the matrix room when I had a question. And most of the times I’d still hold out hope for solving something by myself when I have the strength to pick it up later. But it also makes sense because there’d be no way to differentiate that from me not doing anything. Also around 75% of the time I’ve drafted out questions, I found out an answer along the way. From now on I realise instead of just asking questions, I should think of it as a logging / progress-updating activity first which sounds obvious in hindsight.

To regex or not to regex

The next part where I was stuck at was in converting a pattern that involved custom placeholders like {{CAR_ROT:4d}} or {{:3d}} to their regex counterparts like (\d){3}, (\d){16} etc without using like a l o t of regex, any less complex method than using a conversion function etc. However, after a quick conversation with the mentors and I realised that I had been mistakenly assuming that strftime required regex patterns. Earlier I thought that regex would no longer be part of the end-user experience but still somehow exist in the codebase but this is when I realised that we can entirely do away with it.

Rewrite then Remove? 💀

I also realised that the _extractDateURL() function was made redundant after rewriting it since I found out later that it was only called at one place and that part of the code was no longer required thanks to the existence of a parse-pattern. That’s a nice message to keep in mind for the future.

Modern Day Cain

Another question I encountered was if we could assume that any {year:2d} or %y type 2-digit year xx to be interpreted to be in the 21st century like 20xx or not.

Issue found

I also found this bug in the codebase: In the current scraper._check_timerange(), it takes the simpler way if we provide it with an extractor // parse-pattern and a more complex way if we don’t, however as it is implemented right now

from import Scraper
from sunpy.time import TimeRange
s = Scraper('%Y.fits')
s._check_timerange('2014.fits', TimeRange("2015-01-01", "2015-01-02"))

would return True and it is intended that way in the tests but if we passed it an extractor // parse pattern

s.extractor = "{year:4d}.fits"
s._check_timerange('2014.fits', TimeRange("2015-01-01", "2015-01-02"))

it’d return False.

Inclusivity is important

Failing tests required me to inqure if we want closed-intervals in the package or open, which concluded with closed. I also found other instances in the codebase where we endorse closed intervals.

Future steps

Cover why the rest of tests are breaking and fix em. Ask for review once everything works. Try to come up with a way to write parse-patterns so as the length remains less by trying to minimize repeated values. Also fix my Hugo setup before the night -_-