Skip to content

py/objtype: Validate that __len__ returns an int. - #19647

Open
pablogventura wants to merge 4 commits into
micropython:masterfrom
pablogventura:py-len-validate-type
Open

py/objtype: Validate that __len__ returns an int.#19647
pablogventura wants to merge 4 commits into
micropython:masterfrom
pablogventura:py-len-validate-type

Conversation

@pablogventura

@pablogventura pablogventura commented Aug 24, 2026 •
edited
Loading

Copy link
Copy Markdown

Summary

Fixes #19512. instance_unary_op already validates that __hash__ / __int__ return an int, but MP_UNARY_OP_LEN fell through unchecked, so len(obj) could return None / str / float.

Fold MP_UNARY_OP_LEN into the existing MP_UNARY_OP_INT_MAYBE arm (approach from @jseop-lim on the issue). Non-int __len__ results raise TypeError. This also covers callers that go through instance unary_op.

Testing

  • tests/basics/builtin_len_user.py (int OK; None / str / tuple -> TypeError)
  • tests/run-tests.py basics/builtin_len_user.py on unix standard and minimal

Trade-offs and Alternatives

Code size (unix standard, clean rebuild, size text section):

Version bytes vs master
master 796150 -
this commit 796150 0

instance_unary_op in objtype.o grows by 8 bytes; the linked binary text is unchanged (section padding).

Does not reject a negative __len__ (not free; left for a separate discussion as on the issue).

Deliberate divergence vs CPython: __len__ returning bool raises TypeError here (mp_obj_is_int excludes bool), same as __int__ / #19203. Not covered in the test so the harness can compare against CPython.

Generative AI

I used generative AI tools when creating this PR, but a human has checked the
code and is responsible for the code and the description above.

pablogventura and others added 2 commits August 24, 2026 11:12
@pablogventura @jseop-lim
py/objtype: Validate that __len__ returns an int.
5a1a409 
Fold MP_UNARY_OP_LEN into the existing INT_MAYBE arm so a non-int
__len__ result raises TypeError, matching the zero-cost approach
discussed in micropython#19512.

Co-authored-by: Jeongseop Lim <jseoplim@gmail.com>
Signed-off-by: Pablo Ventura <pablogventura@gmail.com>
@pablogventura
tests/basics: Avoid float and bytearray in builtin_len_user.
37befc0 
Keep the test runnable on the unix minimal variant (no float
literals, no bytearray).

Signed-off-by: Pablo Ventura <pablogventura@gmail.com>
@github-actions

github-actions Bot commented Aug 24, 2026 •
edited
Loading

Copy link
Copy Markdown

Code size report:

Reference:  all: Bump version to 1.29.0. [0fd6c57]
Comparison: ci: Retrigger unix port after stackless_clang flake. [merge of a6a12f8]
  mpy-cross:   +16 +0.004% 
   bare-arm:    +4 +0.007% 
minimal x86:    +5 +0.003% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
      esp32:    +4 +0.000% ESP32_GENERIC
     mimxrt:    +0 +0.000% TEENSY40
        rp2:    +0 +0.000% RPI_PICO_W
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS
  qemu rv32:    +6 +0.001% VIRT_RV32

@codecov

codecov Bot commented Aug 24, 2026 •
edited
Loading

Copy link
Copy Markdown

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.55%. Comparing base (0fd6c57) to head (a6a12f8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files 
@@            Coverage Diff             @@
##           master   #19647      +/-   ##
==========================================
- Coverage   98.58%   98.55%   -0.04%     
==========================================
  Files         182      182              
  Lines       23322    23322              
  Branches        5        5              
==========================================
- Hits        22993    22985       -8     
- Misses        328      336       +8     
  Partials        1        1
Flag Coverage Δ
unix-coverage-32bit 98.55% <ø> (-0.04%) ⬇️
unix-coverage-64bit 98.52% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:
  • ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
  • 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

@pablogventura
ci: Retrigger unix port after unrelated qemu_arm flake.
795b9ad 
Signed-off-by: Pablo Ventura <pablogventura@gmail.com>
@pablogventura
ci: Retrigger unix port after stackless_clang flake.
a6a12f8 
Signed-off-by: Pablo Ventura <pablogventura@gmail.com>
@dpgeorge dpgeorge added py-core Relates to py/ directory in source board-definition New or updated board definition files. Combine with a port- label. and removed board-definition New or updated board definition files. Combine with a port- label. labels Aug 25, 2026
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

No reviews

Assignees

No one assigned

Labels

py-core Relates to py/ directory in source

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

len() does not validate the value returned by __len__

2 participants

@pablogventura @dpgeorge