Refactor fetching function

[carmocca]

What does this PR do?

The previous implementations had some code smells. This PR simplifies it.

Part of #11515

Does your PR introduce any breaking changes? If yes, please list them.

None user-facing

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cc @Borda @justusschock @awaelchli @akihironitta @rohitgr7 @ninginthecloud

[tchaton]

Nice !

[ethanwharris]

LGTM, small comment

[codecov]

Codecov Report

Merging #11516 (829db52) into master (d50b48e) will increase coverage by 0%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #11516    +/-   ##
========================================
  Coverage      92%      92%            
========================================
  Files         194      194            
  Lines       16975    17751   +776     
========================================
+ Hits        15614    16389   +775     
- Misses       1361     1362     +1