PyPAC - Python Proxy Auto-Config

0.17.2 · active · verified Thu Apr 16

PyPAC is a Python library that provides proxy auto-config (PAC) and proxy auto-discovery (WPAD) functionality. It enables applications to automatically determine and use the correct proxy server based on a PAC script, crucial for environments requiring complex proxy logic. The current version is 0.17.2, and it maintains a moderate release cadence, with several minor releases annually addressing bug fixes and minor enhancements.

Common errors

```
pypac.parser.proxy_resolver.ProxyResolutionError: No PAC file found.
```
cause PyPAC could not locate a PAC file through auto-discovery (WPAD) or no explicit PAC URL/path was provided.

fix Provide the PAC file's URL or local path explicitly: `resolver = PACProxyResolver(url='http://your.proxy.com/proxy.pac')` or `session = PACSession(pac_url='file:///path/to/proxy.pac')`.
```
AttributeError: 'PACSession' object has no attribute 'proxies'
```
cause `PACSession` from `pypac` is designed to handle proxy resolution internally and does not expose a settable `.proxies` attribute like a standard `requests.Session` object.

fix Do not attempt to set or access `session.proxies` directly. `PACSession` automatically applies the resolved proxy. If you need to see what proxy was used, inspect `response.request.proxy_url` after a request has been made.
```
ModuleNotFoundError: No module named 'requests'
```
cause You are trying to use `pypac.PACSession` but the `requests` library is not installed.

fix `PACSession` integrates with `requests`. Install it with: `pip install requests` (or `pip install pypac requests`).

Warnings

gotcha When using `PACSession` for `requests` integration, do not attempt to set `session.proxies` manually. `PACSession` transparently handles proxy resolution and setting, and directly modifying `session.proxies` will override or conflict with its functionality.
Fix: Rely on `PACSession` to manage proxies automatically. If you need to inspect proxy usage, check `response.request.proxy_url` after a request.
gotcha PAC file auto-discovery (WPAD) can be unreliable or disabled in some network environments (e.g., corporate networks, firewalls). If `PACSession` or `PACProxyResolver` cannot find a PAC file, it will fall back to a direct connection, which might not be desired.
Fix: If auto-discovery fails, explicitly provide the PAC file URL or path: `PACSession(pac_url='http://your.proxy.com/proxy.pac')` or `PACProxyResolver(url='...')`.
gotcha Python 2.7 support is deprecated and requires the `dukpy` library for PAC script evaluation, which itself has specific installation and versioning requirements for older Python. For modern use, Python 3 is strongly recommended.
Fix: Migrate to Python 3. If Python 2.7 is mandatory, ensure `dukpy>=0.2.3` is installed and be aware of potential platform-specific issues.

Install

pip install pypac Install core library
pip install pypac requests Install with requests integration

Imports

PACProxyResolver
```
from pypac import PACProxyResolver
```
PACSession
```
from pypac import PACSession
```

Quickstart

This quickstart demonstrates how to use PyPAC's `PACSession` to automatically resolve and apply proxy settings for `requests` calls. `PACSession` handles PAC file discovery (e.g., via WPAD) and proxy resolution transparently. If no PAC file is found via auto-discovery, it will default to direct connections.

from pypac import PACSession
import requests

try:
    # Auto-discovers PAC files or manually specify via PACSession(pac_url='...')
    with PACSession() as session:
        # Example usage with a public IP checker (ensure it's HTTP/HTTPS)
        response = session.get('http://httpbin.org/ip')
        response.raise_for_status()
        print(f"Using PACSession, IP is: {response.json()['origin']}")
except requests.exceptions.RequestException as e:
    print(f"Request failed: {e}")
except Exception as e:
    print(f"An unexpected error occurred: {e}")

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