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jinja2 3.1.6: Jinja2 strips a single trailing newline from the end of a template by default, unless keep_trailing_newline is True.

검증된 샘플 — pypi jinja2 3.1.6: Jinja2 strips a single trailing newline from the end of a template by default, unless keep_trailing_newline is True. python 3.12…

sha256:151132e403f9a779c9ff2830e0b4b238d3ad9e805142f28d60695f1b07a1318a

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실행 증거

선언된 환경과 서명된 실행을 분리해 두었습니다. 이 샘플이 무엇을 어디서 실행했는지 그대로 볼 수 있습니다.

증거 기준
서명된 컨트랙트 통과
검증 영수증
3
빌드한 서명 키
3
선언된 환경 python linux x64 python python pip

검증 실행 환경

환경 컨트랙트 단계 실행일
python 3.12 · linux alpine/x64 · docker ed25519:d91480838ac982c9 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · python@1		 2026-08-18
python 3.12 · linux alpine/x64 · docker ed25519:2175b912ea1c23b1 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · python@1		 2026-08-18
python 3.12 · linux debian/x64 · docker ed25519:c1973797be207ac4 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · python@1python:3.12-slim@sha256:09f7da3bc104…		 2026-09-07

케이스

HOW
목표
Jinja2 strips a single trailing newline from the end of a template by default, unless keep_trailing_newline is True.
패키지
심벌
  • keep_trailing_newline
환경
python
생성일
2026-08-18T09:45:40Z

컨트랙트

  1. Environment().from_string('hello\n').render() returns 'hello' rather than 'hello\n', because the default is to strip exactly one trailing newline.
  2. assert jinja2.Environment().from_string('hello\n').render() == 'hello'
  3. assert jinja2.Environment().from_string('hello\n\n').render() == 'hello\n'
  4. assert jinja2.Environment(keep_trailing_newline=True).from_string('hello\n').render() == 'hello\n'

파일

  • NOTES.md
  • csx.json
  • requirements.txt
  • test/contract.py

소스 아티팩트 내려받기 (tar.gz)

소스

NOTES.md
# Jinja2 keep_trailing_newline Behavior

- **search_known_solution answered**: `NO_SAFE_MATCH`
- **Pinned Version**: 3.1.6
- **Observed Behavior**: By default, Jinja2 silently strips a single trailing newline from a template when rendering it, which contradicts the common expectation that template strings ending with a newline will render with that newline intact. Passing `keep_trailing_newline=True` to the `Environment` prevents this stripping. If multiple newlines exist at the end, exactly one is stripped.

When a competent model confidently writes code concatenating rendered strings expecting them to end in newlines, it silently produces improperly formatted text instead of throwing a visible error, making it a subtle trap for configurations generating line-separated outputs.
csx.json
{"case":{"believed":"a template string ending with a newline will render with that newline intact by default","caseId":"case:sha256:589ee88e85e281b8a01dc5c1fc89557ee63793551e28198b136eefa3aad6a0b8","contract":["Environment().from_string('hello\\n').render() returns 'hello' rather than 'hello\\n', because the default is to strip exactly one trailing newline.","assert jinja2.Environment().from_string('hello\\n').render() == 'hello'","assert jinja2.Environment().from_string('hello\\n\\n').render() == 'hello\\n'","assert jinja2.Environment(keep_trailing_newline=True).from_string('hello\\n').render() == 'hello\\n'"],"goal":"Jinja2 strips a single trailing newline from the end of a template by default, unless keep_trailing_newline is True.","kind":"HOW","packages":["pkg:pypi/jinja2@3.1.6"],"schemaVersion":1,"symbols":["keep_trailing_newline"]},"contractCommand":["python","test/contract.py"],"environment":{"arch":"x64","ecosystem":"pypi","executionContext":"python","language":"python","os":"linux","packageManager":"pip","runtime":"python","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/jinja2@3.1.6"],"schemaVersion":1,"symbols":["keep_trailing_newline"],"verifierAdapter":"python@1"}
requirements.txt
Jinja2==3.1.6
MarkupSafe==3.0.3
test/contract.py
import sys
import jinja2

env_default = jinja2.Environment()
env_keep = jinja2.Environment(keep_trailing_newline=True)

# A naive model expects a template ending with a newline to render with that newline.
# By default, Jinja2 strips a single trailing newline.
if env_default.from_string("hello\n").render() != "hello":
    print("Failed: default behavior did not strip the trailing newline.")
    sys.exit(1)

if env_default.from_string("hello\n\n").render() != "hello\n":
    print("Failed: default behavior did not strip exactly one trailing newline.")
    sys.exit(1)

# With keep_trailing_newline=True, the trailing newline is preserved.
if env_keep.from_string("hello\n").render() != "hello\n":
    print("Failed: keep_trailing_newline=True did not preserve the trailing newline.")
    sys.exit(1)

print("All assertions passed.")

오리진 시더

csx-seed