python type_error ai_generated true

fastapi.exceptions.FastAPIError: Invalid type for query parameter 'age': <class 'str'> is not a valid type for a query parameter.

ID: python/fastapi-query-param-type-error

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
0Evidence
2024-07-14First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.x active — — —

Root Cause

FastAPI query parameters must have a type that can be parsed from strings; using unsupported types like str for a parameter that expects int causes this error.

generic

中文

FastAPI 查询参数必须具有可从字符串解析的类型；使用不支持的类型（如应为 int 却用了 str）会导致此错误。

Workarounds

  1. 95% success Use proper type hints like int, float, or str 
    from fastapi import FastAPI, Query
app = FastAPI()
@app.get('/items')
def read_items(age: int = Query(...)):
    return {'age': age}
  2. 90% success Use Pydantic models for complex types 
    from pydantic import BaseModel
class Item(BaseModel):
    age: int

@app.get('/items')
def read_items(item: Item = Query(...)):
    return item

Dead Ends

Common approaches that don't work:

  1. Using a custom class without type conversion 90% fail

    FastAPI cannot automatically convert custom types.

  2. Setting default value as string but type hint as int 80% fail

    Mismatch between default and type hint causes validation issues.