What is a ConnectionError?

A ConnectionError is raised in Python when a network operation fails to establish or maintain a connection. In the standard library it is a base class for network-related OSError subclasses. The requests library re-uses this name for HTTP connection failures.

Why it happens

• •The target server is not running or is not reachable at the specified host and port.
• •A firewall or network policy is blocking the connection.
• •The URL has a typo, wrong port, or incorrect protocol (http vs https).
• •The connection was established but dropped unexpectedly mid-request due to a timeout or server restart.

Examples

import requests

response = requests.get("http://localhost:8080/api/health")
print(response.status_code)

Traceback (most recent call last):
  ...
requests.exceptions.ConnectionError: HTTPConnectionPool(host='localhost', port=8080):
Max retries exceeded with url: /api/health
(Caused by NewConnectionError: Failed to establish a new connection:
[Errno 111] Connection refused)

import requests
from requests.exceptions import ConnectionError as RequestsConnectionError

try:
    response = requests.get("http://localhost:8080/api/health", timeout=5)
    print(response.status_code)
except RequestsConnectionError:
    print("Service is unavailable. Check that it is running.")

Related errors

• ImportError
• TypeError