spylang/spy

Tuple unpacking in for loops

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#455 opened on Apr 7, 2026

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good first issuehelp wanted

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Description

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The following currently fails:

def main() -> None:
    lst = [(1, 2), (3, 4)]
    for (a, b) in lst:
        print(a + b)

❯ spy /tmp/x.spy 
Traceback (most recent call last):

ParseError: not implemented yet: complex for loop targets
  | /tmp/x.spy:3
  |     for (a, b) in lst:
  |         |____| this is not supported

We should support it.

I think that the easiest way is to improve ASTFrame._desugar_for, specifically here: https://github.com/spylang/spy/blob/1c6ad6bdb59541c44b43a55830b2ff6b8c03427c/spy/vm/astframe.py#L755-L765

Instead of generating an ast.Assign node, we should generate an ast.UnpackAssign node.

Contributor guide

Research direction
Examine the ` desugar for` method in `spy/vm/astframe.py` at line 755, and replace the generation of `ast.Assign` with `ast.UnpackAssign` to support tuple unpacking in for loops.
Tech stack
python
Domain
compilers
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitPython
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65