feat: add ternary operator

[charles-cooper]

What I did

fix #3055

How I did it

How to verify it

Commit message

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Description for the changelog

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[codecov-commenter]

Codecov Report

Merging #3398 (422442c) into master (d9e376c) will increase coverage by 0.04%.
The diff coverage is 88.88%.

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@@            Coverage Diff             @@
##           master    #3398      +/-   ##
==========================================
+ Coverage   88.92%   88.96%   +0.04%     
==========================================
  Files          86       86              
  Lines       10726    10760      +34     
  Branches     2440     2443       +3     
==========================================
+ Hits         9538     9573      +35     
- Misses        787      788       +1     
+ Partials      401      399       -2     

Impacted Files	Coverage Δ
vyper/semantics/analysis/annotation.py	87.63% <60.00%> (-1.64%)	⬇️
vyper/ast/nodes.py	94.24% <100.00%> (+0.01%)	⬆️
vyper/codegen/expr.py	87.94% <100.00%> (+0.35%)	⬆️
vyper/semantics/analysis/local.py	91.90% <100.00%> (+0.09%)	⬆️
vyper/semantics/analysis/utils.py	92.33% <100.00%> (+0.20%)	⬆️

... and 2 files with indirect coverage changes

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[fubuloubu]

Moar test cases, but looks solid

[pcaversaccio]

We should maybe add a nested test as well. I plan to use nested ternary operators in my Merkle multiproof contract here:

b = (leaves[leaf_pos] if leaf_pos < leaves_length else hashes[hash_pos]) if flag else proof[proof_pos]

[charles-cooper]

We should maybe add a nested test as well. I plan to use nested ternary operators in my Merkle multiproof contract here:

b = (leaves[leaf_pos] if leaf_pos < leaves_length else hashes[hash_pos]) if flag else proof[proof_pos]

It's right here: https://github.com/vyperlang/vyper/pull/3398/files#diff-59aca5215be5acc4bc64451f64da58d8a2e777bd306a104dfa07a0db6ca34771R237

[pcaversaccio]

Oh missed that one - awesome!