# APIException for FastAPI
[](https://pypi.org/project/APIException/)
[](https://akutayural.github.io/APIException/)
[](https://pepy.tech/project/APIException)
[](https://pypi.org/project/APIException/)
[](https://opensource.org/licenses/MIT)
[](https://github.com/psf/black)
[](https://akutayural.github.io/APIException/)
**APIException** is a fully extensible exception-handling library for **FastAPI**, designed to help you **standardize error responses**, **manage custom error codes**, and ensure **predictable, well-documented APIs** — from day one.
- 🔒 Consistent JSON responses for **both** success and errors.
- 📚 Beautiful Swagger/OpenAPI documentation with clear error cases.
- ⚙️ Customizable error codes with `BaseExceptionCode`.
- 🔗 Global fallback for unhandled server-side errors.
- 🗂️ Use with **multiple FastAPI apps**.
- 📜 Automatic logging of every exception detail.
- ✔️ Production-ready with unit test examples.
· [**View on PyPI**](https://pypi.org/project/APIException)
· [**Full Documentation**](https://akutayural.github.io/APIException/)
Reading the [full documentation](https://akutayural.github.io/APIException/) is **highly recommended** — it’s clear, thorough, and helps you get started in minutes.
---
## 📦 Installation
```bash
pip install APIException==0.1.12
```
---
## ⚡ Quickstart
**1️⃣ Register the Handler**
```python
from APIException import register_exception_handlers
from fastapi import FastAPI
app = FastAPI()
register_exception_handlers(app) # uses ResponseModel by default
# Use raw dict instead:
# register_exception_handlers(app, use_response_model=False)
```
---
## 🔍 See It In Action
```python
from fastapi import FastAPI, Path
from APIException import APIException, ExceptionStatus, register_exception_handlers, ResponseModel, APIResponse, BaseExceptionCode
from pydantic import BaseModel
app = FastAPI()
# Register exception handlers globally to have the consistent
# error handling and response structure
register_exception_handlers(app=app)
# Create the validation model for your response
class UserResponse(BaseModel):
id: int
username: str
# Define your custom exception codes extending BaseExceptionCode
class CustomExceptionCode(BaseExceptionCode):
USER_NOT_FOUND = ("USR-404", "User not found.", "The user ID does not exist.")
INVALID_API_KEY = ("API-401", "Invalid API key.", "Provide a valid API key.")
PERMISSION_DENIED = ("PERM-403", "Permission denied.", "Access to this resource is forbidden.")
@app.get("/user/{user_id}",
response_model=ResponseModel[UserResponse],
responses=APIResponse.custom(
(401, CustomExceptionCode.INVALID_API_KEY),
(403, CustomExceptionCode.PERMISSION_DENIED)
)
)
async def user(user_id: int = Path()):
if user_id == 1:
raise APIException(
error_code=CustomExceptionCode.USER_NOT_FOUND,
http_status_code=401,
)
data = UserResponse(id=1, username="John Doe")
return ResponseModel[UserResponse](
data=data,
description="User found and returned."
)
```
---
**2️⃣ Raise an Exception**
```python
from APIException import APIException, ExceptionCode, register_exception_handlers
from fastapi import FastAPI
app = FastAPI()
register_exception_handlers(app)
@app.get("/login")
async def login(username: str, password: str):
if username != "admin" or password != "admin":
raise APIException(
error_code=ExceptionCode.AUTH_LOGIN_FAILED,
http_status_code=401
)
return {"message": "Login successful!"}
```
---
**3️⃣ Use ResponseModel for Success Responses**
```python
from APIException import ResponseModel, register_exception_handlers
from fastapi import FastAPI
app = FastAPI()
register_exception_handlers(app)
@app.get("/success")
async def success():
return ResponseModel(
data={"foo": "bar"},
message="Everything went fine!"
)
```
**_Response Model In Abstract:_**
---
## 🧩 Custom Error Codes
Always extend BaseExceptionCode — don’t subclass ExceptionCode directly!
```python
from APIException import BaseExceptionCode
class CustomExceptionCode(BaseExceptionCode):
USER_NOT_FOUND = ("USR-404", "User not found.", "User does not exist.")
INVALID_API_KEY = ("API-401", "Invalid API key.", "Key missing or invalid.")
```
And use it:
```python
from APIException import APIException
raise APIException(
error_code=CustomExceptionCode.USER_NOT_FOUND,
http_status_code=404
)
```
---
## ⚙️ Override Default HTTP Status Codes
```python
from APIException import set_default_http_codes
set_default_http_codes({
"FAIL": 422,
"WARNING": 202
})
```
---
## 🌐 Multiple Apps Support
```python
from fastapi import FastAPI
from APIException import register_exception_handlers
mobile_app = FastAPI()
admin_app = FastAPI()
merchant_app = FastAPI()
register_exception_handlers(mobile_app)
register_exception_handlers(admin_app)
register_exception_handlers(merchant_app)
```
---
## 📝 Automatic Logging
Every APIException automatically logs:
- File name & line number
- Error code, status, message, description
Or use the built-in logger:
```python
from APIException import logger
logger.info("Custom info log")
logger.error("Custom error log")
```
---
## ✅ Testing Example
```python
import unittest
from APIException import APIException, ExceptionCode, ResponseModel
class TestAPIException(unittest.TestCase):
def test_api_exception(self):
exc = APIException(error_code=ExceptionCode.AUTH_LOGIN_FAILED)
self.assertEqual(exc.status.value, "FAIL")
def test_response_model(self):
res = ResponseModel(data={"foo": "bar"})
self.assertEqual(res.status.value, "SUCCESS")
if __name__ == "__main__":
unittest.main()
```
**Run the Tests**
- To run the tests, you can use the following command in your terminal:
```bash
python -m unittest discover -s tests
```
---
## 🔗 Full Documentation
Find detailed guides and examples in the [official docs](https://akutayural.github.io/APIException/).
---
## 📜 Changelog
**v0.1.13 (2025-07-21)**
✅ **Initial stable version**
- /examples/fastapi_usage.py has been updated.
- 422 Pydantic error has been fixed in APIResponse.default()
- Documentation has been updated.
- Exception Args has been added to the logs.
- Readme has been updated. New gifs have been added.
**v0.1.12 (2025-07-14)**
- /examples/fastapi_usage.py has been updated.
- 422 Pydantic error has been handled in register_handler
- Documentation has been added.
- `use_fallback_middleware` has been added.
**v0.1.11 (2025-07-13)**
- Added CLI entrypoint (api_exception-info)
- Stable test suite with FastAPI TestClient
- Multiple app support
- Raw dict or Pydantic output
- Automatic logging improvements
**v0.1.0 (2025-06-25)**
🚀 Prototype started!
- Project scaffolding
- `ResponseModel` has been added
- `APIException` has been added
- Defined base ideas for standardizing error handling
---
## License
This project is licensed under the MIT License. See the [LICENSE](./LICENSE) file for more details.
If you like this library and find it useful, don’t forget to give it a ⭐ on GitHub!
## Contact
If you have any questions or suggestions, please feel free to reach out at [ahmetkutayural.dev](https://ahmetkutayural.dev/#contact)
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"description": "# APIException for FastAPI\n[](https://pypi.org/project/APIException/)\n[](https://akutayural.github.io/APIException/)\n[](https://pepy.tech/project/APIException)\n[](https://pypi.org/project/APIException/)\n[](https://opensource.org/licenses/MIT)\n[](https://github.com/psf/black)\n[](https://akutayural.github.io/APIException/)\n\n**APIException** is a fully extensible exception-handling library for **FastAPI**, designed to help you **standardize error responses**, **manage custom error codes**, and ensure **predictable, well-documented APIs** \u2014 from day one.\n\n- \ud83d\udd12 Consistent JSON responses for **both** success and errors.\n- \ud83d\udcda Beautiful Swagger/OpenAPI documentation with clear error cases.\n- \u2699\ufe0f Customizable error codes with `BaseExceptionCode`.\n- \ud83d\udd17 Global fallback for unhandled server-side errors.\n- \ud83d\uddc2\ufe0f Use with **multiple FastAPI apps**.\n- \ud83d\udcdc Automatic logging of every exception detail.\n- \u2714\ufe0f Production-ready with unit test examples.\n\n\u00b7 [**View on PyPI**](https://pypi.org/project/APIException) \n\n\u00b7 [**Full Documentation**](https://akutayural.github.io/APIException/)\n\nReading the [full documentation](https://akutayural.github.io/APIException/) is **highly recommended** \u2014 it\u2019s clear, thorough, and helps you get started in minutes.\n\n---\n\n## \ud83d\udce6 Installation\n\n```bash\npip install APIException==0.1.12\n```\n\n\n\n---\n\n## \u26a1 Quickstart\n\n**1\ufe0f\u20e3 Register the Handler**\n\n```python\nfrom APIException import register_exception_handlers\nfrom fastapi import FastAPI\n\napp = FastAPI()\nregister_exception_handlers(app) # uses ResponseModel by default\n\n# Use raw dict instead:\n# register_exception_handlers(app, use_response_model=False)\n```\n\n---\n\n## \ud83d\udd0d See It In Action\n\n```python\nfrom fastapi import FastAPI, Path\nfrom APIException import APIException, ExceptionStatus, register_exception_handlers, ResponseModel, APIResponse, BaseExceptionCode\nfrom pydantic import BaseModel\n\napp = FastAPI()\n\n# Register exception handlers globally to have the consistent\n# error handling and response structure\nregister_exception_handlers(app=app)\n\n# Create the validation model for your response\nclass UserResponse(BaseModel):\n id: int\n username: str\n\n# Define your custom exception codes extending BaseExceptionCode\nclass CustomExceptionCode(BaseExceptionCode):\n USER_NOT_FOUND = (\"USR-404\", \"User not found.\", \"The user ID does not exist.\")\n INVALID_API_KEY = (\"API-401\", \"Invalid API key.\", \"Provide a valid API key.\")\n PERMISSION_DENIED = (\"PERM-403\", \"Permission denied.\", \"Access to this resource is forbidden.\")\n\n\n@app.get(\"/user/{user_id}\",\n response_model=ResponseModel[UserResponse],\n responses=APIResponse.custom(\n (401, CustomExceptionCode.INVALID_API_KEY),\n (403, CustomExceptionCode.PERMISSION_DENIED)\n )\n)\nasync def user(user_id: int = Path()):\n if user_id == 1:\n raise APIException(\n error_code=CustomExceptionCode.USER_NOT_FOUND,\n http_status_code=401,\n )\n data = UserResponse(id=1, username=\"John Doe\")\n return ResponseModel[UserResponse](\n data=data,\n description=\"User found and returned.\"\n )\n```\n\n\n\n---\n\n\n\n**2\ufe0f\u20e3 Raise an Exception**\n\n```python\nfrom APIException import APIException, ExceptionCode, register_exception_handlers\nfrom fastapi import FastAPI\napp = FastAPI()\n\nregister_exception_handlers(app)\n\n@app.get(\"/login\")\nasync def login(username: str, password: str):\n if username != \"admin\" or password != \"admin\":\n raise APIException(\n error_code=ExceptionCode.AUTH_LOGIN_FAILED,\n http_status_code=401\n )\n return {\"message\": \"Login successful!\"}\n```\n\n---\n\n**3\ufe0f\u20e3 Use ResponseModel for Success Responses**\n\n```python\nfrom APIException import ResponseModel, register_exception_handlers\nfrom fastapi import FastAPI\napp = FastAPI()\n\nregister_exception_handlers(app)\n\n@app.get(\"/success\")\nasync def success():\n return ResponseModel(\n data={\"foo\": \"bar\"},\n message=\"Everything went fine!\"\n )\n```\n\n**_Response Model In Abstract:_**\n\n\n\n\n\n---\n\n## \ud83e\udde9 Custom Error Codes\n\nAlways extend BaseExceptionCode \u2014 don\u2019t subclass ExceptionCode directly!\n\n```python\nfrom APIException import BaseExceptionCode\n\nclass CustomExceptionCode(BaseExceptionCode):\n USER_NOT_FOUND = (\"USR-404\", \"User not found.\", \"User does not exist.\")\n INVALID_API_KEY = (\"API-401\", \"Invalid API key.\", \"Key missing or invalid.\")\n```\n\nAnd use it:\n\n```python\nfrom APIException import APIException\n\nraise APIException(\n error_code=CustomExceptionCode.USER_NOT_FOUND,\n http_status_code=404\n)\n```\n\n---\n\n## \u2699\ufe0f Override Default HTTP Status Codes\n\n```python\nfrom APIException import set_default_http_codes\n\nset_default_http_codes({\n \"FAIL\": 422,\n \"WARNING\": 202\n})\n```\n\n---\n\n## \ud83c\udf10 Multiple Apps Support\n```python\nfrom fastapi import FastAPI\nfrom APIException import register_exception_handlers\n\nmobile_app = FastAPI()\nadmin_app = FastAPI()\nmerchant_app = FastAPI()\n\nregister_exception_handlers(mobile_app)\nregister_exception_handlers(admin_app)\nregister_exception_handlers(merchant_app)\n```\n\n---\n\n## \ud83d\udcdd Automatic Logging\n\nEvery APIException automatically logs:\n\n- File name & line number\n\n- Error code, status, message, description\n\nOr use the built-in logger:\n\n```python\nfrom APIException import logger\n\nlogger.info(\"Custom info log\")\nlogger.error(\"Custom error log\")\n```\n\n---\n\n## \u2705 Testing Example\n\n```python\nimport unittest\nfrom APIException import APIException, ExceptionCode, ResponseModel\n\nclass TestAPIException(unittest.TestCase):\n def test_api_exception(self):\n exc = APIException(error_code=ExceptionCode.AUTH_LOGIN_FAILED)\n self.assertEqual(exc.status.value, 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