FA-2976 / Text processing / Open access

Removing a prefix eats a set of leading characters · case 01

Removing a prefix eats a set of leading characters.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Remove the exact leading text prefix pre: once.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Remove the exact leading text prefix pre: once.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Remove the exact leading text prefix pre: once.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x.lstrip('pre:')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('pre:prep'), 'prep')
check('boundary 2', solve('peer'), 'peer')
check('boundary 3', solve('pre:pre:x'), 'pre:x')
check('boundary 4', solve('xpre:'), 'xpre:')
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1		`prep`	Failed
boundary 2		`peer`	Failed
boundary 3	`x`	`pre:x`	Failed
boundary 4	`xpre:`	`xpre:`	Passed

SHA-256 / a1bfef970e619408971b5a639489743e8d74e700e9b3d449f61b51acb30b276f

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x.replace('pre:','')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('pre:prep'), 'prep')
check('boundary 2', solve('peer'), 'peer')
check('boundary 3', solve('pre:pre:x'), 'pre:x')
check('boundary 4', solve('xpre:'), 'xpre:')
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`prep`	`prep`	Passed
boundary 2	`peer`	`peer`	Passed
boundary 3	`x`	`pre:x`	Failed
boundary 4	`x`	`xpre:`	Failed

SHA-256 / 29a1ccb05c4c68767662b320a1c1cf6edfe79266f546d6fe9795fe8c91d75bba

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x.removeprefix('pre:')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('pre:prep'), 'prep')
check('boundary 2', solve('peer'), 'peer')
check('boundary 3', solve('pre:pre:x'), 'pre:x')
check('boundary 4', solve('xpre:'), 'xpre:')
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
boundary 1	`prep`	`prep`	Passed
boundary 2	`peer`	`peer`	Passed
boundary 3	`pre:x`	`pre:x`	Passed
boundary 4	`xpre:`	`xpre:`	Passed

SHA-256 / 0a772269b22788e74dd63dad19ff7e91a0796679a35380e4cb7a7218acf57a86

Verification & scope

This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:37:19.794244+00:00.

Case digest / 334c9fdeb8962f75850dd0bc99799cefb415cc98a1690276b722e7c2613e230a