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Zhongwei Li
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.claude/skills/error-handling-completeness/SKILL.md
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.claude/skills/error-handling-completeness/SKILL.md
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---
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name: error-handling-completeness
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description: Evaluates if error handling is sufficient for new code - checks try-catch coverage, logging, user messages, retry logic. Focuses on external calls and user-facing code.
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---
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# Error Handling Completeness Skill
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**Purpose**: Prevent production crashes with systematic error handling.
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**Trigger Words**: API call, external, integration, network, database, file, user input, async, promise, await
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---
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## Quick Decision: Needs Error Handling Check?
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```python
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def needs_error_check(code_context: dict) -> bool:
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"""Decide if error handling review is needed."""
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# High-risk operations (always check)
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high_risk = [
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"fetch", "axios", "requests", "http", # HTTP calls
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"db.", "query", "execute", # Database
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"open(", "read", "write", # File I/O
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"json.loads", "json.parse", # JSON parsing
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"int(", "float(", # Type conversions
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"subprocess", "exec", # External processes
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"await", "async", # Async operations
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]
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code = code_context.get("code", "").lower()
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return any(risk in code for risk in high_risk)
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```
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---
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## Error Handling Checklist (Fast)
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### 1. **External API Calls** (Most Critical)
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```python
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# ❌ BAD - No error handling
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def get_user_data(user_id):
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response = requests.get(f"https://api.example.com/users/{user_id}")
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return response.json() # What if network fails? 404? Timeout?
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# ✅ GOOD - Complete error handling
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def get_user_data(user_id):
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try:
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response = requests.get(
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f"https://api.example.com/users/{user_id}",
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timeout=5 # Timeout!
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)
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response.raise_for_status() # Check HTTP errors
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return response.json()
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except requests.Timeout:
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logger.error(f"Timeout fetching user {user_id}")
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raise ServiceUnavailableError("User service timeout")
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except requests.HTTPError as e:
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if e.response.status_code == 404:
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raise UserNotFoundError(f"User {user_id} not found")
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logger.error(f"HTTP error fetching user: {e}")
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raise
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except requests.RequestException as e:
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logger.error(f"Network error: {e}")
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raise ServiceUnavailableError("Cannot reach user service")
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```
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**Quick Checks**:
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- ✅ Timeout set?
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- ✅ HTTP errors handled?
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- ✅ Network errors caught?
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- ✅ Logged?
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- ✅ User-friendly error returned?
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---
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### 2. **Database Operations**
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```python
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# ❌ BAD - Swallows errors
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def delete_user(user_id):
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try:
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db.execute("DELETE FROM users WHERE id = ?", [user_id])
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except Exception:
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pass # Silent failure!
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# ✅ GOOD - Specific handling
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def delete_user(user_id):
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try:
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result = db.execute("DELETE FROM users WHERE id = ?", [user_id])
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if result.rowcount == 0:
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raise UserNotFoundError(f"User {user_id} not found")
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except db.IntegrityError as e:
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logger.error(f"Cannot delete user {user_id}: {e}")
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raise DependencyError("User has related records")
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except db.OperationalError as e:
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logger.error(f"Database error: {e}")
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raise DatabaseUnavailableError()
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```
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**Quick Checks**:
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- ✅ Specific exceptions (not bare `except`)?
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- ✅ Logged?
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- ✅ User-friendly error?
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---
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### 3. **File Operations**
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```python
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# ❌ BAD - File might not exist
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def read_config():
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with open("config.json") as f:
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return json.load(f)
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# ✅ GOOD - Handle missing file
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def read_config():
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try:
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with open("config.json") as f:
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return json.load(f)
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except FileNotFoundError:
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logger.warning("config.json not found, using defaults")
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return DEFAULT_CONFIG
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except json.JSONDecodeError as e:
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logger.error(f"Invalid JSON in config.json: {e}")
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raise ConfigurationError("Malformed config.json")
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except PermissionError:
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logger.error("Permission denied reading config.json")
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raise
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```
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**Quick Checks**:
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- ✅ FileNotFoundError handled?
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- ✅ JSON parse errors caught?
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- ✅ Permission errors handled?
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---
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### 4. **Type Conversions**
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```python
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# ❌ BAD - Crash on invalid input
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def process_age(age_str):
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age = int(age_str) # What if "abc"?
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return age * 2
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# ✅ GOOD - Validated
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def process_age(age_str):
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try:
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age = int(age_str)
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if age < 0 or age > 150:
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raise ValueError("Age out of range")
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return age * 2
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except ValueError:
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raise ValidationError(f"Invalid age: {age_str}")
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```
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**Quick Checks**:
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- ✅ ValueError caught?
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- ✅ Range validation?
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- ✅ Clear error message?
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---
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### 5. **Async/Await** (JavaScript/Python)
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```javascript
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// ❌ BAD - Unhandled promise rejection
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async function fetchUser(id) {
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const user = await fetch(`/api/users/${id}`);
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return user.json(); // What if network fails?
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}
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// ✅ GOOD - Handled
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async function fetchUser(id) {
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try {
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const response = await fetch(`/api/users/${id}`);
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if (!response.ok) {
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throw new Error(`HTTP ${response.status}`);
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}
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return await response.json();
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} catch (error) {
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console.error(`Failed to fetch user ${id}:`, error);
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throw new ServiceError("Cannot fetch user");
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}
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}
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```
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**Quick Checks**:
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- ✅ Try-catch around await?
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- ✅ HTTP status checked?
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- ✅ Logged?
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---
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## Error Handling Patterns
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### Pattern 1: Retry with Exponential Backoff
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```python
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def call_api_with_retry(url, max_retries=3):
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for attempt in range(max_retries):
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try:
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response = requests.get(url, timeout=5)
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response.raise_for_status()
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return response.json()
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except requests.Timeout:
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if attempt < max_retries - 1:
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wait = 2 ** attempt # 1s, 2s, 4s
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logger.warning(f"Timeout, retrying in {wait}s...")
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time.sleep(wait)
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else:
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raise
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```
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**When to use**: Transient failures (network, rate limits)
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---
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### Pattern 2: Fallback Values
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```python
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def get_user_avatar(user_id):
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try:
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return fetch_from_cdn(user_id)
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except CDNError:
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logger.warning(f"CDN failed for user {user_id}, using default")
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return DEFAULT_AVATAR_URL
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```
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**When to use**: Non-critical operations, graceful degradation
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---
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### Pattern 3: Circuit Breaker
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```python
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class CircuitBreaker:
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def __init__(self, max_failures=5):
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self.failures = 0
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self.max_failures = max_failures
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self.is_open = False
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def call(self, func):
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if self.is_open:
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raise ServiceUnavailableError("Circuit breaker open")
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try:
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result = func()
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self.failures = 0 # Reset on success
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return result
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except Exception as e:
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self.failures += 1
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if self.failures >= self.max_failures:
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self.is_open = True
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logger.error("Circuit breaker opened")
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raise
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```
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**When to use**: Preventing cascading failures
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---
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## Output Format
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```markdown
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## Error Handling Report
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**Status**: [✅ COMPLETE | ⚠️ GAPS FOUND]
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---
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### Missing Error Handling: 3
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1. **[HIGH] No timeout on API call (api_client.py:45)**
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- **Issue**: `requests.get()` has no timeout
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- **Risk**: Indefinite hang if service slow
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- **Fix**:
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```python
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response = requests.get(url, timeout=5)
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```
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2. **[HIGH] Unhandled JSON parse error (config.py:12)**
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- **Issue**: `json.load()` not wrapped in try-catch
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- **Risk**: Crash on malformed JSON
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- **Fix**:
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```python
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try:
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config = json.load(f)
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except json.JSONDecodeError as e:
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logger.error(f"Invalid JSON: {e}")
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return DEFAULT_CONFIG
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```
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3. **[MEDIUM] Silent exception swallowing (db.py:89)**
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- **Issue**: `except Exception: pass`
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- **Risk**: Failures go unnoticed
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- **Fix**: Log error or use specific exception
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---
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**Good Practices Found**: 2
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- ✅ Database errors logged properly (db.py:34)
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- ✅ Retry logic on payment API (payments.py:67)
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---
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**Next Steps**:
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1. Add timeout to API calls (5 min)
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2. Wrap JSON parsing in try-catch (2 min)
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3. Remove silent exception handlers (3 min)
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```
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---
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## What This Skill Does NOT Do
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❌ Catch every possible exception (too noisy)
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❌ Force try-catch everywhere (only where needed)
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❌ Replace integration tests
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❌ Handle business logic errors (validation, etc.)
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✅ **DOES**: Check critical error-prone operations (network, I/O, parsing)
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---
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## Configuration
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```bash
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# Strict mode: check all functions
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export LAZYDEV_ERROR_HANDLING_STRICT=1
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# Disable error handling checks
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export LAZYDEV_DISABLE_ERROR_CHECKS=1
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```
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---
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**Version**: 1.0.0
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**Focus**: External calls, I/O, parsing, async
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**Speed**: <2 seconds per file
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