Sample
Pin MarkupSafe __html__ protocol evaluation discrepancies between format() and escape(), format specifier rejections, % helper type errors, and mutation auto-escaping
sha256:ee43604c2b3d1d7c19c6e5ac416478456ecd9af20d85dc3e8accdb54f51b8ba8
PUBLISHED
L3_CONTRACT_PASS
MIT-0
Execution evidence
Declared environment and signed verification runs are separated so you can see exactly what this sample proves.
Evidence basisSigned contract pass
Verification receipts1
Verification levelL3_CONTRACT_PASS
Declared environment
- Execution context
- python
- Operating system
- linux
- Architecture
- x64
- Runtime
- python
- Language
- python
- Package manager
- pip
Verification-run environments
- Execution context
- python 3.12
- Operating system
- linux alpine · musl
- Architecture
- x64
- Runtime
- python 3.12
- Language
- python
- Package manager
- pip
- Execution
- container · docker
CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-17
Case
- Goal
- Pin MarkupSafe __html__ protocol evaluation discrepancies between format() and escape(), format specifier rejections, % helper type errors, and mutation auto-escaping HOW
- Packages
-
markupsafe 3.0.3
- Environment
- python
- Created
- 2026-08-17T19:16:48Z
Commonly assumed
Markup.format() treats objects returning str from __html__() as pre-escaped HTML identically to escape() and % interpolation.
The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.
Contract
- Markup.format() escapes plain str returns from __html__() into HTML entities because EscapeFormatter wraps format_field results in escape(), requiring __html__() to return Markup or define __html_format__ for unescaped formatting
- assert Markup.format() with format specifiers raises ValueError on Markup instances and classes defining only __html__
- assert Markup % interpolation fails with TypeError on %x, %X, %o, and %c because _MarkupEscapeHelper lacks __index__
- assert Markup.replace auto-escapes plain string replacements and padding methods fail with TypeError on HTML fillchar
- assert Markup.striptags and unescape return plain str which re-escapes when combined with Markup
- assert soft_str preserves Markup instances to prevent double escaping when re-passed to escape
Files
- NOTES.md
- csx.json
- requirements.txt
- src/__init__.py
- src/formatter.py
- test/contract.py
Download the source artifact (tar.gz)
Origin Seeder
csx-seed
Verification receipts
- python 3.12 · linux alpine/x64 · docker · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-17 · ed25519:d91480838ac982c9