Advanced Usage

Customizing pool behavior

The PoolManager class automatically handles creating ConnectionPool instances for each host as needed. By default, it will keep a maximum of 10 ConnectionPool instances. If you’re making requests to many different hosts it might improve performance to increase this number:

>>> import urllib3
>>> http = urllib3.PoolManager(num_pools=50)

However, keep in mind that this does increase memory and socket consumption.

Similarly, the ConnectionPool class keeps a pool of individual HTTPConnection instances. These connections are used during an individual request and returned to the pool when the request is complete. By default only one connection will be saved for re-use. If you are making many requests to the same host simultaneously it might improve performance to increase this number:

>>> import urllib3
>>> http = urllib3.PoolManager(maxsize=10)
# Alternatively
>>> http = urllib3.HTTPConnectionPool('google.com', maxsize=10)

The behavior of the pooling for ConnectionPool is different from PoolManager. By default, if a new request is made and there is no free connection in the pool then a new connection will be created. However, this connection will not be saved if more than maxsize connections exist. This means that maxsize does not determine the maximum number of connections that can be open to a particular host, just the maximum number of connections to keep in the pool. However, if you specify block=True then there can be at most maxsize connections open to a particular host:

>>> http = urllib3.PoolManager(maxsize=10, block=True)
# Alternatively
>>> http = urllib3.HTTPConnectionPool('google.com', maxsize=10, block=True)

Any new requests will block until a connection is available from the pool. This is a great way to prevent flooding a host with too many connections in multi-threaded applications.

Streaming and IO

When dealing with large responses it’s often better to stream the response content:

>>> import urllib3
>>> http = urllib3.PoolManager()
>>> r = http.request(
...     'GET',
...     'http://httpbin.org/bytes/1024',
...     preload_content=False)
>>> for chunk in r.stream(32):
...     print(chunk)
b'...'
b'...'
...
>>> r.release_conn()

Setting preload_content to False means that urllib3 will stream the response content. stream() lets you iterate over chunks of the response content.

Note

When using preload_content=False, you should call release_conn() to release the http connection back to the connection pool so that it can be re-used.

However, you can also treat the HTTPResponse instance as a file-like object. This allows you to do buffering:

>>> r = http.request(
...     'GET',
...     'http://httpbin.org/bytes/1024',
...     preload_content=False)
>>> r.read(4)
b'\x88\x1f\x8b\xe5'

Calls to read() will block until more response data is available.

>>> import io
>>> reader = io.BufferedReader(r, 8)
>>> reader.read(4)
>>> r.release_conn()

You can use this file-like object to do things like decode the content using codecs:

>>> import codecs
>>> reader = codecs.getreader('utf-8')
>>> r = http.request(
...     'GET',
...     'http://httpbin.org/ip',
...     preload_content=False)
>>> json.load(reader(r))
{'origin': '127.0.0.1'}
>>> r.release_conn()

Proxies

You can use ProxyManager to tunnel requests through an HTTP proxy:

>>> import urllib3
>>> proxy = urllib3.ProxyManager('http://localhost:3128/')
>>> proxy.request('GET', 'http://google.com/')

The usage of ProxyManager is the same as PoolManager.

You can use SOCKSProxyManager to connect to SOCKS4 or SOCKS5 proxies. In order to use SOCKS proxies you will need to install PySocks or install urllib3 with the socks extra:

pip install urllib3[socks]

Once PySocks is installed, you can use SOCKSProxyManager:

>>> from urllib3.contrib.socks import SOCKSProxyManager
>>> proxy = SOCKSProxyManager('socks5://localhost:8889/')
>>> proxy.request('GET', 'http://google.com/')

Custom SSL certificates and client certificates

Instead of using certifi you can provide your own certificate authority bundle. This is useful for cases where you’ve generated your own certificates or when you’re using a private certificate authority. Just provide the full path to the certificate bundle when creating a PoolManager:

>>> import urllib3
>>> http = urllib3.PoolManager(
...     cert_reqs='CERT_REQUIRED',
...     ca_certs='/path/to/your/certificate_bundle')

When you specify your own certificate bundle only requests that can be verified with that bundle will succeed. It’s recommended to use a separate PoolManager to make requests to URLs that do not need the custom certificate.

You can also specify a client certificate. This is useful when both the server and the client need to verify each other’s identity. Typically these certificates are issued from the same authority. To use a client certificate, provide the full path when creating a PoolManager:

>>> http = urllib3.PoolManager(
...     cert_file='/path/to/your/client_cert.pem',
...     cert_reqs='CERT_REQUIRED',
...     ca_certs='/path/to/your/certificate_bundle')

Certificate validation and Mac OS X

Apple-provided Python and OpenSSL libraries contain a patches that make them automatically check the system keychain’s certificates. This can be surprising if you specify custom certificates and see requests unexpectedly succeed. For example, if you are specifying your own certificate for validation and the server presents a different certificate you would expect the connection to fail. However, if that server presents a certificate that is in the system keychain then the connection will succeed.

This article has more in-depth analysis and explanation.

If you have homebrew, you can configure homebrew Python to use homebrew’s OpenSSL instead of the system OpenSSL:

brew install openssl
brew install python --with-brewed-openssl

SSL Warnings

urllib3 will issue several different warnings based on the level of certificate verification support. These warning indicate particular situations and can resolved in different ways.

  • InsecureRequestWarning

    This happens when an request is made to an HTTPS URL without certificate verification enabled. Follow the certificate verification guide to resolve this warning.

  • InsecurePlatformWarning

    This happens on Python 2 platforms that have an outdated ssl module. These older ssl modules can cause some insecure requests to succeed where they should fail and secure requests to fail where they should succeed. Follow the pyOpenSSL guide to resolve this warning.

  • SNIMissingWarning

    This happens on Python 2 versions older than 2.7.9. These older versions lack SNI support. This can cause servers to present a certificate that the client thinks is invalid. Follow the pyOpenSSL guide to resolve this warning.

Making unverified HTTPS requests is strongly discouraged, however, if you understand the risks and wish to disable these warnings, you can use disable_warnings():

>>> import urllib3
>>> urllib3.disable_warnings()

Alternatively you can capture the warnings with the standard logging module:

>>> logging.captureWarnings(True)

Finally, you can suppress the warnings at the interpreter level by setting the PYTHONWARNINGS environment variable or by using the -W flag.

Google App Engine

urllib3 supports Google App Engine with some caveats.

If you’re using the Flexible environment, you do not have to do any configuration- urllib3 will just work. However, if you’re using the Standard environment then you either have to use urllib3.contrib.appengine‘s AppEngineManager or use the Sockets API

To use AppEngineManager:

>>> from urllib3.contrib.appengine import AppEngineManager
>>> http = AppEngineManager()
>>> http.request('GET', 'https://google.com/')

To use the Sockets API, add the following to your app.yaml and use PoolManager as usual:

env_variables:
    GAE_USE_SOCKETS_HTTPLIB : 'true'

For more details on the limitations and gotchas, see urllib3.contrib.appengine.