Serialization Errors

Symptoms

• JSON encoding errors

• Stack traces mentioning non-serializable objects

• Malformed log output

Causes

• Passing complex objects in log kwargs

• Circular references

• Non-JSON types (datetime, Decimal) without conversion

Fixes

from fapilog import get_async_logger

logger = await get_async_logger()

payload = {
    "user_id": user.id,
    "created_at": user.created_at.isoformat(),  # convert datetime
    "preferences": dict(user.preferences),       # convert custom objects
}

await logger.info("User data", **payload)

Tips:

• Convert datetimes to ISO strings, enums to strings, complex objects to dicts.

• Keep kwargs shallow; avoid deeply nested custom classes.