From 071a046987037c4c5545a62e15fab39c5775741c Mon Sep 17 00:00:00 2001
From: SvDp <svdp028@gmail.com>
Date: Fri, 28 Nov 2025 16:24:12 +0530
Subject: [PATCH] Add __str__ methods to validation error classes for better
 debugging

Added human-readable string representations to RequestValidationError and
WebSocketRequestValidationError classes, consistent with the existing
ResponseValidationError implementation. This improves developer experience
when debugging validation errors by providing clear, formatted error messages.

Changes:
- Add __str__ method to RequestValidationError
- Add __str__ method to WebSocketRequestValidationError
- Add comprehensive tests for the new string representations

The string format shows the number of errors and lists each error on a
separate line, making it easier to read error messages during debugging
and logging.
---
 fastapi/exceptions.py              | 18 ++++++++-
 tests/test_validation_error_str.py | 65 ++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 tests/test_validation_error_str.py

diff --git a/fastapi/exceptions.py b/fastapi/exceptions.py
index 0620428be..10549b33c 100644
--- a/fastapi/exceptions.py
+++ b/fastapi/exceptions.py
@@ -167,9 +167,25 @@ class RequestValidationError(ValidationException):
         super().__init__(errors)
         self.body = body
 
+    def __str__(self) -> str:
+        message = f"{len(self._errors)} validation error"
+        if len(self._errors) > 1:
+            message += "s"
+        message += " for request:\n"
+        for err in self._errors:
+            message += f"  {err}\n"
+        return message
+
 
 class WebSocketRequestValidationError(ValidationException):
-    pass
+    def __str__(self) -> str:
+        message = f"{len(self._errors)} validation error"
+        if len(self._errors) > 1:
+            message += "s"
+        message += " for WebSocket request:\n"
+        for err in self._errors:
+            message += f"  {err}\n"
+        return message
 
 
 class ResponseValidationError(ValidationException):
diff --git a/tests/test_validation_error_str.py b/tests/test_validation_error_str.py
new file mode 100644
index 000000000..26f5d6447
--- /dev/null
+++ b/tests/test_validation_error_str.py
@@ -0,0 +1,65 @@
+"""Tests for __str__ methods of validation exceptions."""
+
+from fastapi.exceptions import (
+    RequestValidationError,
+    ResponseValidationError,
+    WebSocketRequestValidationError,
+)
+
+
+def test_request_validation_error_str_single_error():
+    """Test string representation of RequestValidationError with single error."""
+    errors = [{"type": "int_parsing", "loc": ["query", "id"], "msg": "Input should be a valid integer"}]
+    exc = RequestValidationError(errors)
+    result = str(exc)
+
+    assert "1 validation error for request:" in result
+    assert "{'type': 'int_parsing'" in result
+
+
+def test_request_validation_error_str_multiple_errors():
+    """Test string representation of RequestValidationError with multiple errors."""
+    errors = [
+        {"type": "int_parsing", "loc": ["query", "id"], "msg": "Input should be a valid integer"},
+        {"type": "missing", "loc": ["query", "name"], "msg": "Field required"},
+    ]
+    exc = RequestValidationError(errors)
+    result = str(exc)
+
+    assert "2 validation errors for request:" in result
+    assert "int_parsing" in result
+    assert "missing" in result
+
+
+def test_websocket_request_validation_error_str_single_error():
+    """Test string representation of WebSocketRequestValidationError with single error."""
+    errors = [{"type": "int_parsing", "loc": ["query", "id"], "msg": "Input should be a valid integer"}]
+    exc = WebSocketRequestValidationError(errors)
+    result = str(exc)
+
+    assert "1 validation error for WebSocket request:" in result
+    assert "{'type': 'int_parsing'" in result
+
+
+def test_websocket_request_validation_error_str_multiple_errors():
+    """Test string representation of WebSocketRequestValidationError with multiple errors."""
+    errors = [
+        {"type": "int_parsing", "loc": ["query", "id"], "msg": "Input should be a valid integer"},
+        {"type": "missing", "loc": ["query", "name"], "msg": "Field required"},
+    ]
+    exc = WebSocketRequestValidationError(errors)
+    result = str(exc)
+
+    assert "2 validation errors for WebSocket request:" in result
+    assert "int_parsing" in result
+    assert "missing" in result
+
+
+def test_response_validation_error_str_consistency():
+    """Test that ResponseValidationError has similar __str__ behavior."""
+    errors = [{"type": "int_parsing", "loc": ["response", "id"], "msg": "Input should be a valid integer"}]
+    exc = ResponseValidationError(errors)
+    result = str(exc)
+
+    assert "1 validation error" in result
+    assert "{'type': 'int_parsing'" in result