fix deprecation warnings for collections.abc (will break in Python 3.9)

[terencehonles]

No description provided.

[codecov-io]

Codecov Report

Merging #1865 into develop will increase coverage by 0.11%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop    #1865      +/-   ##
===========================================
+ Coverage    92.56%   92.67%   +0.11%     
===========================================
  Files           53       53              
  Lines        10000    10181     +181     
===========================================
+ Hits          9256     9435     +179     
- Misses         744      746       +2

Impacted Files	Coverage Δ
botocore/session.py	98.13% <100%> (+0.01%)	⬆️
botocore/awsrequest.py	98.37% <100%> (+0.01%)	⬆️
botocore/configprovider.py	93.37% <0%> (-0.09%)	⬇️
botocore/client.py	99.73% <0%> (-0.03%)	⬇️
botocore/auth.py	98.3% <0%> (-0.03%)	⬇️
botocore/args.py	100% <0%> (ø)	⬆️
botocore/exceptions.py	99.41% <0%> (+0.01%)	⬆️
botocore/signers.py	98.52% <0%> (+0.02%)	⬆️
botocore/httpsession.py	92.48% <0%> (+0.04%)	⬆️
... and 3 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2f8950d...4176d97. Read the comment docs.

[b4stien]

FYI the title seems misleading: it breaks with the newly released Python 3.8, not the next-year unreleased 3.9. We haven't tested yet, but the message seems straightforward about this:

/opt/api_venv/lib/python3.7/site-packages/botocore/awsrequest.py:624: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working

[toolness]

Thanks, it would be great to see this PR merged!

@b4stien it looks like they actually pushed the removal to 3.9 when they released 3.8--see #1615 (comment) or this Twitter thread for more details.

[terencehonles]

@toolness I didn't realize it moved! I thought I just remembered it incorrectly.

I had checked the Python source and saw it in 3.8 when I was checking this and itypes, which I had on an ignore list for the DeprecationWarning and was preparing to start testing against 3.8.

[Syntactical01]

Is this fixed yet? I feel like this should be a higher priority item. Lambda supports 3.8 yet we cannot safely use boto3 in Python 3.8 because of this deprecation. This is still an issue in botocore, moto, and boto.

[tirkarthi]

There is one more instance in tests which could also be fixed with the PR :

botocore/tests/unit/test_parsers.py

Line 28 in 5fb69ec

class CustomHeaderDict(collections.MutableMapping):

[tirkarthi]

Python 3.9 will raise an ImportError as per upstream PR : python/cpython#10596

[thompsjj]

Will anyone ever merge this?

[terencehonles]

@tirkarthi thanks, I updated the test!

Now to get this merged 🤔...

[terencehonles]

This is no longer needed with #1922 which does the same thing.