FA-4021 / Delimited text / Open access

A backslash-escaped delimiter is treated as a field boundary · case 01

A backslash-escaped delimiter is treated as a field boundary.

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: Parse one comma-delimited row with backslash escaping and no quote semantics.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Parse one comma-delimited row with backslash escaping and no quote semantics.

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

Case contract

Parse one comma-delimited row with backslash escaping and no quote semantics.

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.split(',')
    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('a\\,b,c'), ['a,b', 'c'])
check('boundary 2', solve('"a,b"'), ['"a', 'b"'])
check('boundary 3', solve('a\\\\b'), ['a\\b'])
check('boundary 4', solve('a,,'), ['a', '', ''])
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	`['a\\', 'b', 'c']`	`['a,b', 'c']`	Failed
boundary 2	`['"a', 'b"']`	`['"a', 'b"']`	Passed
boundary 3	`['a\\\\b']`	`['a\\b']`	Failed
boundary 4	`['a', '', '']`	`['a', '', '']`	Passed

SHA-256 / 2872b407b33cb872a987cdab7cf00f6a446f23bb2e648f94a30d35fcfa4bbe0e

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 next(csv.reader([x],escapechar="\\"))
    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('a\\,b,c'), ['a,b', 'c'])
check('boundary 2', solve('"a,b"'), ['"a', 'b"'])
check('boundary 3', solve('a\\\\b'), ['a\\b'])
check('boundary 4', solve('a,,'), ['a', '', ''])
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	`['a,b', 'c']`	`['a,b', 'c']`	Passed
boundary 2	`['a,b']`	`['"a', 'b"']`	Failed
boundary 3	`['a\\b']`	`['a\\b']`	Passed
boundary 4	`['a', '', '']`	`['a', '', '']`	Passed

SHA-256 / 0b7db9821deb1239412411bb23855610950d4b869ff71be07858260197887191

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 next(csv.reader([x],escapechar="\\",quoting=csv.QUOTE_NONE))
    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('a\\,b,c'), ['a,b', 'c'])
check('boundary 2', solve('"a,b"'), ['"a', 'b"'])
check('boundary 3', solve('a\\\\b'), ['a\\b'])
check('boundary 4', solve('a,,'), ['a', '', ''])
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	`['a,b', 'c']`	`['a,b', 'c']`	Passed
boundary 2	`['"a', 'b"']`	`['"a', 'b"']`	Passed
boundary 3	`['a\\b']`	`['a\\b']`	Passed
boundary 4	`['a', '', '']`	`['a', '', '']`	Passed

SHA-256 / e53816ed8f38ebd763cca6805ef46b99a0292fd98e8342652df8a39e6eeec749

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 2026-09-29T14:37:34.556047+00:00.

Case digest / 36c03ebe042e5fedaa5086469b14aa912a967fbf4c235ac1867002d60d1a222a