python data_error ai_generated true

pydantic_core._pydantic_core.ValidationError: 1 validation error for Event timestamp Input should be a valid datetime, invalid date separator, expected 'T' or ' ' [type=datetime_parsing, input_value='2024-01-15_10:30:00', input_type=str]

ID: python/pydantic-validation-error-datetime-parsing

Also available as: JSON · Markdown · 中文
80%Fix Rate
86%Confidence
0Evidence
2024-09-11First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

The datetime string uses an invalid separator (e.g. underscore). Pydantic v2 uses RFC 3339 / ISO 8601 parsing and requires 'T' or a space between date and time.

generic

中文

datetime 字符串使用了无效的分隔符（如下划线）。Pydantic v2 使用 RFC 3339 / ISO 8601 解析，要求日期与时间之间用 'T' 或空格分隔。

Workarounds

  1. 95% success 
    value = '2024-01-15_10:30:00'.replace('_', 'T', 1)
  2. 92% success 
    from datetime import datetime
from pydantic import BaseModel, field_validator

class Event(BaseModel):
    timestamp: datetime

    @field_validator('timestamp', mode='before')
    @classmethod
    def parse_dt(cls, v):
        if isinstance(v, str):
            return datetime.strptime(v, '%Y-%m-%d_%H:%M:%S')
        return v

Dead Ends

Common approaches that don't work:

  1. 60% fail

    strptime works but bypasses Pydantic validation, so type errors surface later as AttributeError.

  2. 75% fail

    Loses timezone-aware comparison and arithmetic capabilities.