ConnectionPools — urllib3 1.16 documentation

# ConnectionPools

A connection pool is a container for a collection of connections to a specific host.

If you need to make requests to the same host repeatedly, then you should use a `HTTPConnectionPool`.

    >>> from urllib3 import HTTPConnectionPool
    >>> pool = HTTPConnectionPool('ajax.googleapis.com', maxsize=1)
    >>> r = pool.request('GET', '/ajax/services/search/web',
    ...                  fields={'q': 'urllib3', 'v': '1.0'})
    >>> r.status
    200
    >>> r.headers['content-type']
    'text/javascript; charset=utf-8'
    >>> 'data: ' + r.data # Content of the response
    'data: ...'
    >>> r = pool.request('GET', '/ajax/services/search/web',
    ...                  fields={'q': 'python', 'v': '1.0'})
    >>> 'data: ' + r.data # Content of the response
    'data: ...'
    >>> pool.num_connections
    1
    >>> pool.num_requests
    2

By default, the pool will cache just one connection. If you’re planning on using such a pool in a multithreaded environment, you should set the `maxsize` of the pool to a higher number, such as the number of threads. You can also control many other variables like timeout, blocking, and default headers.

A ConnectionPool can be used as a context manager to automatically clear the pool after usage.

    >>> from urllib3 import HTTPConnectionPool
    >>> with HTTPConnectionPool('ajax.googleapis.com', maxsize=1) as pool:
    ...     r = pool.request('GET', '/ajax/services/search/web',
    ...                      fields={'q': 'urllib3', 'v': '1.0'})
    ...     print(pool.pool)
    ...
    <queue.LifoQueue object at 0x7f67367dfcf8>
    >>> print(pool.pool)
    None

## Helpers

There are various helper functions provided for instantiating these ConnectionPools more easily:

> `urllib3.connectionpool.` `connection_from_url`(url, **kw)

>   Given a url, return an `ConnectionPool` instance of its host.

>   This is a shortcut for not having to parse out the scheme, host, and port of the url before creating an `ConnectionPool` instance.

>   Parameters: | url – Absolute URL string that must include the scheme. Port is optional. **kw – Passes additional parameters to the constructor of the appropriate `ConnectionPool`. Useful for specifying things like timeout, maxsize, headers, etc.

>   Example:

>       >>> conn = connection_from_url('http://google.com/')
>       >>> r = conn.request('GET', '/')

## API

`urllib3.connectionpool` comes with two connection pools:

> class `urllib3.connectionpool.` `HTTPConnectionPool`(host, port=None, strict=False, timeout=<object object>, maxsize=1, block=False, headers=None, retries=None, _proxy=None, _proxy_headers=None, **conn_kw)

>   Thread-safe connection pool for one host.

>   Parameters: | host – Host used for this HTTP Connection (e.g. “localhost”), passed into `httplib.HTTPConnection`. port – Port used for this HTTP Connection (None is equivalent to 80), passed into `httplib.HTTPConnection`. strict – Causes BadStatusLine to be raised if the status line can’t be parsed as a valid HTTP/1.0 or 1.1 status line, passed into `httplib.HTTPConnection`. Note Only works in Python 2. This parameter is ignored in Python 3. timeout – Socket timeout in seconds for each individual connection. This can be a float or integer, which sets the timeout for the HTTP request, or an instance of `urllib3.util.Timeout` which gives you more fine-grained control over request timeouts. After the constructor has been parsed, this is always a urllib3.util.Timeout object. maxsize – Number of connections to save that can be reused. More than 1 is useful in multithreaded situations. If `block` is set to False, more connections will be created but they will not be saved once they’ve been used. block – If set to True, no more than `maxsize` connections will be used at a time. When no free connections are available, the call will block until a connection has been released. This is a useful side effect for particular multithreaded situations where one does not want to use more than maxsize connections per host to prevent flooding. headers – Headers to include with all requests, unless other headers are given explicitly. retries – Retry configuration to use by default with requests in this pool. _proxy – Parsed proxy URL, should not be used directly, instead, see `urllib3.connectionpool.ProxyManager`“ _proxy_headers – A dictionary with proxy headers, should not be used directly, instead, see `urllib3.connectionpool.ProxyManager`“ **conn_kw – Additional parameters are used to create fresh `urllib3.connection.HTTPConnection`, `urllib3.connection.HTTPSConnection` instances.

>   `ConnectionCls`

>     alias of `HTTPConnection`

>   `QueueCls`

>     alias of `LifoQueue`

>   `ResponseCls`

>     alias of `HTTPResponse`

>   `close`()

>     Close all pooled connections and disable the pool.

>   `is_same_host`(url)

>     Check if the given `url` is a member of the same host as this connection pool.

>   `request`(method, url, fields=None, headers=None, **urlopen_kw)

>     Make a request using `urlopen()` with the appropriate encoding of `fields` based on the `method` used.

>     This is a convenience method that requires the least amount of manual effort. It can be used in most situations, while still having the option to drop down to more specific methods when necessary, such as `request_encode_url()`, `request_encode_body()`, or even the lowest level `urlopen()`.

>   `request_encode_body`(method, url, fields=None, headers=None, encode_multipart=True, multipart_boundary=None, **urlopen_kw)

>     Make a request using `urlopen()` with the `fields` encoded in the body. This is useful for request methods like POST, PUT, PATCH, etc.

>     When `encode_multipart=True` (default), then `urllib3.filepost.encode_multipart_formdata()` is used to encode the payload with the appropriate content type. Otherwise `urllib.urlencode()` is used with the ‘application/x-www-form-urlencoded’ content type.

>     Multipart encoding must be used when posting files, and it’s reasonably safe to use it in other times too. However, it may break request signing, such as with OAuth.

>     Supports an optional `fields` parameter of key/value strings AND key/filetuple. A filetuple is a (filename, data, MIME type) tuple where the MIME type is optional. For example:

>         fields = {
>             'foo': 'bar',
>             'fakefile': ('foofile.txt', 'contents of foofile'),
>             'realfile': ('barfile.txt', open('realfile').read()),
>             'typedfile': ('bazfile.bin', open('bazfile').read(),
>                           'image/jpeg'),
>             'nonamefile': 'contents of nonamefile field',
>         }

>     When uploading a file, providing a filename (the first parameter of the tuple) is optional but recommended to best mimick behavior of browsers.

>     Note that if `headers` are supplied, the ‘Content-Type’ header will be overwritten because it depends on the dynamic random boundary string which is used to compose the body of the request. The random boundary string can be explicitly set with the `multipart_boundary` parameter.

>   `request_encode_url`(method, url, fields=None, headers=None, **urlopen_kw)

>     Make a request using `urlopen()` with the `fields` encoded in the url. This is useful for request methods like GET, HEAD, DELETE, etc.

>   `urlopen`(method, url, body=None, headers=None, retries=None, redirect=True, assert_same_host=True, timeout=<object object>, pool_timeout=None, release_conn=None, chunked=False, **response_kw)

>     Get a connection from the pool and perform an HTTP request. This is the lowest level call for making a request, so you’ll need to specify all the raw details.

>     Note

>     More commonly, it’s appropriate to use a convenience method provided by `RequestMethods`, such as `request()`.

>     Note

>     release_conn will only behave as expected if preload_content=False because we want to make preload_content=False the default behaviour someday soon without breaking backwards compatibility.

>     Parameters: | method – HTTP request method (such as GET, POST, PUT, etc.) body – Data to send in the request body (useful for creating POST requests, see HTTPConnectionPool.post_url for more convenience). headers – Dictionary of custom headers to send, such as User-Agent, If-None-Match, etc. If None, pool headers are used. If provided, these headers completely replace any pool-specific headers. retries (`Retry`, False, or an int.) – Configure the number of retries to allow before raising a `MaxRetryError` exception. Pass `None` to retry until you receive a response. Pass a `Retry` object for fine-grained control over different types of retries. Pass an integer number to retry connection errors that many times, but no other types of errors. Pass zero to never retry. If `False`, then retries are disabled and any exception is raised immediately. Also, instead of raising a MaxRetryError on redirects, the redirect response will be returned. redirect – If True, automatically handle redirects (status codes 301, 302, 303, 307, 308). Each redirect counts as a retry. Disabling retries will disable redirect, too. assert_same_host – If `True`, will make sure that the host of the pool requests is consistent else will raise HostChangedError. When False, you can use the pool on an HTTP proxy and request foreign hosts. timeout – If specified, overrides the default timeout for this one request. It may be a float (in seconds) or an instance of `urllib3.util.Timeout`. pool_timeout – If set and the pool is set to block=True, then this method will block for `pool_timeout` seconds and raise EmptyPoolError if no connection is available within the time period. release_conn – If False, then the urlopen call will not release the connection back into the pool once a response is received (but will release if you read the entire contents of the response such as when preload_content=True). This is useful if you’re not preloading the response’s content immediately. You will need to call `r.release_conn()` on the response `r` to return the connection back into the pool. If None, it takes the value of `response_kw.get('preload_content', True)`. chunked – If True, urllib3 will send the body using chunked transfer encoding. Otherwise, urllib3 will send the body using the standard content-length form. Defaults to False. **response_kw – Additional parameters are passed to `urllib3.response.HTTPResponse.from_httplib()`

> class `urllib3.connectionpool.` `HTTPSConnectionPool`(host, port=None, strict=False, timeout=<object object>, maxsize=1, block=False, headers=None, retries=None, _proxy=None, _proxy_headers=None, key_file=None, cert_file=None, cert_reqs=None, ca_certs=None, ssl_version=None, assert_hostname=None, assert_fingerprint=None, ca_cert_dir=None, **conn_kw)

>   Same as `HTTPConnectionPool`, but HTTPS.

>   When Python is compiled with the `ssl` module, then `VerifiedHTTPSConnection` is used, which can verify certificates, instead of `HTTPSConnection`.

>   `VerifiedHTTPSConnection` uses one of `assert_fingerprint`, `assert_hostname` and `host` in this order to verify connections. If `assert_hostname` is False, no verification is done.

>   The `key_file`, `cert_file`, `cert_reqs`, `ca_certs`, `ca_cert_dir`, and `ssl_version` are only used if `ssl` is available and are fed into `urllib3.util.ssl_wrap_socket()` to upgrade the connection socket into an SSL socket.

All of these pools inherit from a common base class:

> class `urllib3.connectionpool.` `ConnectionPool`(host, port=None)

>   Base class for all connection pools, such as `HTTPConnectionPool` and `HTTPSConnectionPool`.

## Related Classes

urllib3 implements its own `HTTPConnection` object to allow for more flexibility than the standard library’s implementation.

class `urllib3.connection.` `HTTPConnection`(*args, **kw)

  Based on httplib.HTTPConnection but provides an extra constructor backwards-compatibility layer between older and newer Pythons.

  Additional keyword parameters are used to configure attributes of the connection. Accepted parameters include:

  > - `strict`: See the documentation on `urllib3.connectionpool.HTTPConnectionPool`

  > - `source_address`: Set the source address for the current connection.

  >   Note

  >   This is ignored for Python 2.6. It is only applied for 2.7 and 3.x

  > - `socket_options`: Set specific options on the underlying socket. If not specified, then defaults are loaded from `HTTPConnection.default_socket_options` which includes disabling Nagle’s algorithm (sets TCP_NODELAY to 1) unless the connection is behind a proxy.

  >   For example, if you wish to enable TCP Keep Alive in addition to the defaults, you might pass:

  >       HTTPConnection.default_socket_options + [
  >           (socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1),
  >       ]

  >   Or you may want to disable the defaults by passing an empty list (e.g., `[]`).

  `default_socket_options` = [(6, 1, 1)]

    Disable Nagle’s algorithm by default. `[(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)]`

  `is_verified` = False

    Whether this connection verifies the host’s certificate.

  `request_chunked`(method, url, body=None, headers=None)

    Alternative to the common request method, which sends the body with chunked encoding and not as one block

  `socket_options` = None

    The socket options provided by the user. If no options are provided, we use the default options.