Question
Answer and Explanation
The error "AttributeError: type object 'bool' has no attribute 'dependency'" in FastAPI typically arises when you're attempting to use a boolean (bool) value where FastAPI expects a dependency callable (a function or class that can be called to resolve dependencies).
Let's break down the common reasons and solutions:
1. Incorrect Dependency Injection:
- FastAPI uses a dependency injection system where functions or classes are specified as dependencies and can be automatically resolved before the route handler is executed. If a bool value is mistakenly passed as a dependency, FastAPI tries to treat it as a callable, hence the error.
- Example of incorrect usage:
from fastapi import FastAPI, Depends
app = FastAPI()
def some_dependency():
return "Dependency Value"
@app.get("/items/{item_id}")
async def read_item(item_id: int, dependency_bool: bool = True): # Incorrect use of bool as dependency
return {"item_id": item_id, "dependency": dependency_bool }
- The correct usage is to use Depends in cases of dependencies:
from fastapi import FastAPI, Depends
app = FastAPI()
def some_dependency():
return "Dependency Value"
@app.get("/items/{item_id}")
async def read_item(item_id: int, dependency = Depends(some_dependency)): # Correct usage of Depends
return {"item_id": item_id, "dependency": dependency }
2. Misuse of Path Parameters:
- Sometimes, you might accidentally define a path parameter in the function signature as a boolean, and while FastAPI can handle type conversions, it doesn't mean it is valid to use the boolean as a dependency.
3. Default Value Conflicts:
- If you have a dependency with a default value that is inadvertently a bool, FastAPI might incorrectly interpret it.
4. Problematic Custom Dependencies:
- When creating custom dependencies using Depends, ensure that each of them returns a value and does not end up returning a bool under some conditions.
How to resolve this error:
1. Review your dependencies: Double-check where you are using Depends(). Ensure that the value inside Depends is always a callable.
2. Check path parameters: If you see a boolean, make sure it's not intended to be a path parameter. Use proper type annotations (e.g., int, str, float) for path parameters.
3. Default values: Avoid having boolean as default values for dependency parameters unless explicitly intended.
4. Inspect your custom dependencies: Go through your custom dependencies and make sure each returns a value, and that no conditional statement or other operation results in returning a boolean where it shouldn't be.
5. Debugging: Use print statements or a debugger to inspect the type of each dependency to find out the cause of the problem.
By addressing these issues, you should be able to resolve the "AttributeError: type object 'bool' has no attribute 'dependency'" error in your FastAPI application.