python type_error ai_generated true

RuntimeError: Dependency cache key must be hashable

ID: python/fastapi-runtimeerror-dependency-cache-key-must-be-hashable

Also available as: JSON · Markdown · 中文
80%Fix Rate
84%Confidence
0Evidence
2024-08-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.x active — — —

Root Cause

Using a mutable object (like a list or dict) as a dependency parameter that FastAPI tries to cache.

generic

中文

使用可变对象（如列表或字典）作为 FastAPI 尝试缓存的依赖参数。

Workarounds

  1. 90% success Use immutable types like tuple instead of list. 
    from typing import Tuple
async def dependency(items: Tuple[int, ...] = (1, 2, 3)):
    return items
  2. 95% success Use Pydantic models for complex parameters. 
    from pydantic import BaseModel
class FilterParams(BaseModel):
    tags: list[str] = []

async def dependency(params: FilterParams):
    return params

Dead Ends

Common approaches that don't work:

  1. Using a list as a default value for a dependency. 80% fail

    Lists are mutable and unhashable, causing caching issues.

  2. Using a dict as a query parameter. 70% fail

    Query parameters must be hashable; dicts are not.