HushLog

Zero-config PII redaction for Python logging.

Features

• Zero-config -- one call to hushlog.patch() and you're done
• Non-invasive -- wraps existing formatters, no logger rewrites needed
• Performant -- pre-compiled regex with heuristic early-exit checks
• Type-safe -- fully typed with PEP 561 py.typed marker
• Python 3.10+ -- supports Python 3.10 through 3.13

Installation

pip install hushlog

Or with uv:

uv add hushlog

Quick Start

import logging
import hushlog

# Configure logging FIRST, then patch
logging.basicConfig(level=logging.INFO)
hushlog.patch()

logger = logging.getLogger(__name__)

logger.info("User email: john@example.com")
# Output: User email: [EMAIL REDACTED]

logger.info("Card: 4111-1111-1111-1111")
# Output: Card: [CREDIT_CARD REDACTED]

logger.info("SSN: 123-45-6789")
# Output: SSN: [SSN REDACTED]

How It Works

HushLog wraps your existing logging formatters with a RedactingFormatter that scans the final formatted string for PII patterns. It never replaces loggers or handlers -- your existing logger.info() calls remain unchanged. All regex patterns are pre-compiled at import time with lightweight heuristic pre-checks to minimize overhead on the hot logging path.

What Gets Redacted

Configuration

Disable specific built-in patterns or add custom ones:

from hushlog import Config

hushlog.patch(Config(
    disable_patterns=frozenset({"phone"}),
    custom_patterns={"internal_id": r"ID-[A-Z]{3}-[0-9]{6}"},
))

Partial Masking

Show partial values instead of full redaction:

hushlog.patch(Config(mask_style="partial"))
# john@example.com → j***@e***.com
# 4111111111111111 → ****-****-****-1111
# 078-05-1120      → ***-**-1120
# (555) 234-5678   → (***) ***-5678

Use a custom mask character:

hushlog.patch(Config(mask_style="partial", mask_character="#"))
# john@example.com → j###@e###.com

Note: Partial masking reveals partial information (first/last characters). In small organizations, this may be identifying. Use mask_style="full" (default) for maximum privacy.

JSON / Structured Logging

HushLog supports JSON log output with automatic PII redaction in all string values, including nested structures.

RedactingJsonFormatter

Use RedactingJsonFormatter as a drop-in JSON formatter for any handler:

import logging
from hushlog import RedactingJsonFormatter

formatter = RedactingJsonFormatter.from_config()

handler = logging.StreamHandler()
handler.setFormatter(formatter)
logging.getLogger().addHandler(handler)

logger = logging.getLogger(__name__)
logger.info("Contact user@example.com", extra={"ssn": "078-05-1120"})
# Output: {"message": "Contact [EMAIL REDACTED]", "ssn": "[SSN REDACTED]", ...}

Works with or without python-json-logger installed. Install the optional dependency for enhanced JSON serialization:

pip install hushlog[json]

redact_dict()

For manual redaction of dict/list/string structures:

import hushlog

data = {"user": {"email": "alice@corp.io", "name": "Alice", "age": 30}}
clean = hushlog.redact_dict(data)
# {"user": {"email": "[EMAIL REDACTED]", "name": "Alice", "age": 30}}

Note: redact_dict() creates a new PatternRegistry on every call. For repeated use, create a registry once via PatternRegistry.from_config() and call registry.redact_dict() directly.

structlog

Use structlog_processor() as a processor in your structlog pipeline:

import structlog
from hushlog import structlog_processor

structlog.configure(
    processors=[
        structlog.stdlib.add_log_level,
        structlog_processor(),
        structlog.dev.ConsoleRenderer(),
    ],
)

logger = structlog.get_logger()
logger.info("login", email="alice@corp.com")
# Output: email=[EMAIL REDACTED]

Install the optional dependency: pip install hushlog[structlog]

loguru

Wrap any loguru sink with PII redaction:

from loguru import logger
from hushlog import loguru_sink

logger.remove()  # Remove default sink
logger.add(loguru_sink(print), format="{message}")

logger.info("User alice@corp.com logged in")
# Output: User [EMAIL REDACTED] logged in

Install the optional dependency: pip install hushlog[loguru]

Teardown

Call unpatch() to remove HushLog's formatter wrappers and restore the original formatters. This is useful for testing or runtime toggling:

hushlog.unpatch()

Calling unpatch() without a prior patch() is safe (no-op). Calling patch() multiple times is also safe (idempotent).

Limitations

• Only handlers present on the root logger at patch() time are wrapped. Handlers added later will not be redacted.
• Named loggers with propagate=False and their own handlers bypass root-level redaction.
• For structlog/loguru, use the dedicated integrations (structlog_processor, loguru_sink) instead of patch().
• Phone detection covers US NANP, Brazilian, Indian, and E.164 international formats.

Security Model

HushLog uses regex-based pattern matching for PII detection. This is a best-effort approach with known trade-offs:

• Heuristic pre-checks (e.g., checking for @ before running email regex) are performance optimizations, not security boundaries. They reduce regex invocations but do not guarantee detection.
• Regex patterns are pre-compiled and tested against common formats, but they cannot detect PII in obfuscated, encrypted, or encoded forms.
• Partial masking (mask_style="partial") reveals partial information by design. In small organizations, first/last characters may be identifying. Use mask_style="full" for maximum privacy.
• Custom patterns are compiled at Config construction and validated, but HushLog does not check for ReDoS vulnerability in user-supplied regex. Use tested patterns from trusted sources.
• Unicode normalization (NFC) is applied before redaction to handle decomposed character forms, but does not protect against confusable characters (homoglyphs like Cyrillic "a" vs Latin "a").

For high-security environments, combine HushLog with additional controls (log access restrictions, encryption at rest, audit logging).

Planned

Production hardening, docs site, and more. See the roadmap for details.

Contributing

Contributions are welcome! See CONTRIBUTING.md for guidelines.

License

MIT -- see LICENSE for details.