Docs/Core Concepts/Error Handling

Error Handling

Learn how to handle errors gracefully in your Predicate automation scripts. Build resilient automation that recovers from failures and provides meaningful error messages.

Common Error Scenarios

Web automation is inherently unreliable. Networks fail, pages change, elements disappear. Proper error handling makes your automation production-ready.

Elements Not Found

The most common error: an element you're looking for doesn't exist.

from predicate import snapshot, find, click

snap = snapshot(browser)
button = find(snap,

Timeout Errors

Operations that take too long should timeout gracefully:

from predicate import wait_for

# Wait with timeout
result = wait_for(browser, "role=heading text~'Success'", timeout=10.0)

if result.found:
    print("Success message appeared!")
else:

Network Errors

Handle network failures during page loads or API calls:

from predicate import PredicateBrowser, snapshot
import time

with PredicateBrowser(api_key="sk_...") as browser:
    max_retries = 3
    retry_count = 0

    while retry_count < max_retries:

Error Handling Patterns

Retry with Exponential Backoff

import time

def retry_with_backoff(func, max_retries=3, base_delay=1):
    """Retry a function with exponential backoff"""
    for attempt in range(max_retries):
        try:

Fallback Strategies

from predicate import snapshot, find, click

snap = snapshot(browser)

# Try primary button first
submit_btn = find(snap, "role=button text~'Submit Form'")

if not submit_btn:
    # Fallback: try alternative text

Graceful Degradation

from predicate import snapshot, find, click, wait_for

def login(browser, email, password):
    """Login with error handling and graceful degradation"""
    try:
        # Navigate to login page
        browser.page.

Logging and Debugging

Structured Logging

import logging

# Configure logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(levelname)s - %(message)s'
)
logger = logging.getLogger(__name__)

# Use in automation
def

Screenshots for Debugging

# Take screenshot on error
try:
    result = wait_for(browser, "role=button text~'submit'", timeout=5.0)
    if not result.found:
        browser.page.screenshot(path="element_not_found.png")
        raise ValueError("Submit button not found")
except Exception as e:
    browser.page.screenshot(path="error_state.png")
    raise

Best Practices

1. Always Validate Element Existence

# Good
button = find(snap, "role=button text~'submit'")
if button:
    click(browser, button.id)
else:
    # Handle missing element

# Avoid
button = find(snap, "role=button text~'submit'")
click(browser, button.id)  # Might crash if button is None

2. Use Appropriate Timeouts

# Short timeout for fast operations
result = wait_for(browser, "role=alert", timeout=2.0)

# Long timeout for slow operations
result = wait_for(browser, "text~'Report generated'", timeout=120.0)

3. Provide Meaningful Error Messages

# Good
if not button:
    raise ValueError(f"Submit button not found with query: {query}. Page might have changed.")

# Avoid
if not button:
    raise ValueError("Error")

4. Clean Up Resources

from predicate import PredicateBrowser

# Use context manager for automatic cleanup
with PredicateBrowser(api_key="sk_...") as browser:
    # Automation code
    pass  # Browser closes automatically

# Or manual cleanup
browser = PredicateBrowser(api_key="sk_...")
try:
    # Automation code
finally:
    browser.close()  # Always close

Common Error Types

ValueError

Element not found or invalid query:

try:
    button = find(snap, "role=button text~'submit'")
    if not button:
        raise ValueError("Submit button not found")
except ValueError as e:
    print(f"Validation error: {e}")

TimeoutError

Operation took too long:

try:
    result = wait_for(browser, "text~'Success'", timeout=10.0)
    if not result.found:
        raise TimeoutError("Success message didn't appear")
except TimeoutError as e:
    print(f"Timeout: {e}")

NetworkError

Network or navigation failures:

try:
    browser.page.goto("https://example.com", timeout=30000)
except Exception as e:
    print(f"Network error: {e}")
    # Retry or fail gracefully

Next Steps

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