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Proxy auto-config and auto-discovery for Python.

Project description

PyPAC is a Python library for finding proxy auto-config (PAC) files and making HTTP requests that respect them. PAC files are often used in organizations that need fine-grained and centralized control of proxy settings.

PyPAC can find PAC files according to the DNS portion of the Web Proxy Auto-Discovery (WPAD) protocol. On Windows, PyPAC will automatically get the PAC file URL from the Internet Options dialog. On macOS, PyPAC will automatically get the PAC file URL from System Preferences.

PyPAC provides a subclass of a Requests Session, so you can start using it immediately, with any PAC file transparently discovered and honoured:

>>> from pypac import PACSession
>>> session = PACSession()
>>> session.get('')

If a PAC file isn’t found, then PACSession behaves like a regular Session.

If you’re looking to add basic PAC functionality to a library that you’re using, try the pac_context_for_url() context manager:

from pypac import pac_context_for_url
import boto3

with pac_context_for_url(''):
    client = boto3.client('sqs')

This sets up proxy environment variables at the start of the scope, based on any auto-discovered PAC and the given URL. pac_context_for_url() should work for any library that honours proxy environment variables.


  • The same Requests API that you already know and love

  • Honour PAC setting from Windows Internet Options and macOS System Preferences

  • Follow DNS Web Proxy Auto-Discovery protocol

  • Proxy authentication pass-through

  • Proxy failover and load balancing

  • Generic components for adding PAC support to other code

PyPAC supports Python 2.7 and 3.5+.


Install PyPAC using pip:

$ python -m pip install pypac


PyPAC’s documentation is available at

0.16.4 (2023-04-24)

0.16.3 (2023-03-31)

  • isInNet(): Return False immediately for invalid host arg. (#71)

0.16.2 (2023-03-26)

  • Handle boolean args to isInNet(). (#69)

  • Remove Python 3.5, 3.6 from CIB test matrix.

  • Windows Python 2.7 CIB: Pin to dukpy 0.2.3.

0.16.1 (2022-11-08)

  • Disable tldextract caching. (#64) Thanks @mpkuth.

0.16.0 (2022-01-01)

  • Change tld dependency to tldextract. (#61)

0.15.0 (2021-02-27)

  • Drop support for Python 3.4. (#48)

  • Support more proxy keywords: HTTP, HTTPS, SOCKS4, SOCKS5. (#41)

  • Absorb any exception from tld.get_tld(), not just TldDomainNotFound. (#30) Thanks @santiavenda2.

  • Reimplement dnsDomainIs(host, domain) as case-insensitive ‘host ends with domain’. (#42, #57)

0.14.0 (2020-12-05)

  • Add ability to supply PACFile to pac_context_for_url(). (#52) Thanks @alexrohvarger.

0.13.0 (2019-09-16)

  • Make it possible to configure the request for the PAC file. (#44) Thanks @SeyfSV.

  • urlencode proxy username and password. (#46) Thanks @aslafy-z.

0.12.0 (2018-09-11)

  • Fix possible error when dnsResolve() fails. (#34) Thanks @maximinus.

0.11.0 (2018-09-08)

  • Require dukpy 0.2.2, to fix memory leak. (#32) Thanks @maximinus.

  • Change Mac environment marker. (#30)

  • Support Python 3.7.

0.10.1 (2018-08-26)

  • Require tld 0.9.x. (#29)

0.10.0 (2018-08-26)

  • Switch JavaScript interpreter to dukpy. (#24)

  • Fix pac_context_for_url() erroring with DIRECT PAC setting. (#27)

  • Fix warning about invalid escape sequence (#26). Thanks @BoboTiG.

0.9.0 (2018-06-02)

  • Add macOS support for PAC in System Preferences (#23). Thanks @LKleinNux.

  • The from_registry argument on pypac.get_pac() and pypac.collect_pac_urls() is now deprecated and will be removed in 1.0.0. Use from_os_settings instead.

0.8.1 (2018-03-01)

  • Defer Js2Py import until it’s needed. It uses a lot of memory. See #20 for details.

0.8.0 (2018-02-28)

  • Add support for file:// PAC URLs on Windows.

0.7.0 (2018-02-21)

  • Drop support for Python 3.3.

  • Add doc explaining how to use pac_context_for_url().

  • Internal changes to dev and test processes.

0.6.0 (2018-01-28)

  • Add pac_context_for_url(), a context manager that adds basic PAC functionality through proxy environment variables.

0.5.0 (2018-01-18)

  • Accept PAC files served with no Content-Type header.

0.4.0 (2017-11-07)

  • Add recursion_limit keyword argument to PACSession and PACFile. The default is an arbitrarily high value (10000), which should cover most applications.

  • Exclude port numbers from host passed to FindProxyForURL(url, host).

0.3.1 (2017-06-23)

  • Update GitHub username.

0.3.0 (2017-04-12)

  • Windows: Get system auto-proxy config setting using winreg module.

  • Windows: Accept local filesystem paths from system proxy auto-config setting.

  • Raise PacComplexityError when recursion limit is hit while parsing PAC file.

  • Support setting PACSession.proxy_auth and ProxyResolver.proxy_auth after constructing an instance.

  • Narrative docs.

0.2.1 (2017-01-19)

  • Require Js2Py >= 0.43 for Python 3.6 support, and to avoid needing to monkeypatch out pyimport.

0.1.0 (2016-06-12)

  • First release.

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