Make order of previous locales deterministic

[surkova]

When using set for storing previously seen locales we eventually end up in the land of non-determinism when looping through them:

Python 3.8.5 (default, Jul 21 2020, 10:48:26)
[Clang 11.0.3 (clang-1103.0.32.62)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = set()
>>> a.add("ru")
>>> a.add("es")
>>> a
{'es', 'ru'}
>>> a.add("en")
>>> a
{'es', 'en', 'ru'}
...

Since python 3.7 insertion order is preserved in dictionaries, so we can take advantage of this.

I'm not sure what the policy is as for support of python < 3.7, on travis we seem to be running even 3.5, then my test will fail there. However, when looking at this discussion, I see there's an appetite for making this logic deterministic. Approach with dict should not be slowing parsing either:

>>> b = {}
>>> b.update({"es": "es"})  # first string parsed
>>> b
{'es': 'es'}
>>> b.update({"ru": "ru"})  # second string parsed
>>> b
{'es': 'es', 'ru': 'ru'}
>>> b.update({"es": "es"})  # third string parsed
>>> b
{'es': 'es', 'ru': 'ru'}
...

[codecov]

Codecov Report

Merging #851 (dc0c1d4) into master (939e722) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #851      +/-   ##
==========================================
+ Coverage   98.33%   98.37%   +0.03%     
==========================================
  Files         231      231              
  Lines        2590     2591       +1     
==========================================
+ Hits         2547     2549       +2     
+ Misses         43       42       -1     

Impacted Files	Coverage Δ
dateparser/date.py	100.00% <100.00%> (ø)
dateparser/languages/dictionary.py	100.00% <0.00%> (+0.67%)	⬆️

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[surkova]

I can change to use collections.OrderedDict if we want to keep this change and need to support < 3.7.

[noviluni]

Good catch @surkova!

Could you kindly address what I added in the comments?

Thanks!

[Gallaecio]

💄

Suggested change

	for locale in self.previous_locales.keys():
	for locale in self.previous_locales:

I’m just mentioning this in case .keys() was not added on purpose. But given .keys() is more explicit, maybe the current code is more readable. ✔️ either way.

[noviluni]

I think we can leave it as-is. For me, it seems more accurate to explicitly indicate that we iterate through the keys. 👍

[noviluni]

Thanks again @surkova! 🚀