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Environment Variables

The HTTPX library can be configured via environment variables. Environment variables are used by default. To ignore environment variables, trust_env has to be set False. There are two ways to set trust_env to disable environment variables:

  • On the client via httpx.Client(trust_env=False).
  • Using the top-level API, such as httpx.get("<url>", trust_env=False).

Here is a list of environment variables that HTTPX recognizes and what function they serve:

HTTPX_LOG_LEVEL

Valid values: debug, trace (case-insensitive)

If set to debug, then HTTP requests will be logged to stderr. This is useful for general purpose reporting of network activity.

If set to trace, then low-level details about the execution of HTTP requests will be logged to stderr, in addition to debug log lines. This can help you debug issues and see what's exactly being sent over the wire and to which location.

Example:

# test_script.py
import httpx

with httpx.Client() as client:
    r = client.get("https://google.com")

Debug output:

$ HTTPX_LOG_LEVEL=debug python test_script.py
DEBUG [2019-11-06 19:11:24] httpx._client - HTTP Request: GET https://google.com "HTTP/1.1 301 Moved Permanently"
DEBUG [2019-11-06 19:11:24] httpx._client - HTTP Request: GET https://www.google.com/ "HTTP/1.1 200 OK"

Trace output:

$ HTTPX_LOG_LEVEL=trace python test_script.py
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection_pool - acquire_connection origin=Origin(scheme='https' host='google.com' port=443)
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection_pool - new_connection connection=HTTPConnection(origin=Origin(scheme='https' host='google.com' port=443))
TRACE [2019-11-06 19:18:56] httpx._config - load_ssl_context verify=True cert=None trust_env=True http_versions=HTTPVersionConfig(['HTTP/1.1', 'HTTP/2'])
TRACE [2019-11-06 19:18:56] httpx._config - load_verify_locations cafile=/Users/florimond/Developer/python-projects/httpx/venv/lib/python3.8/site-packages/certifi/cacert.pem
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection - start_connect host='google.com' port=443 timeout=Timeout(timeout=5.0)
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection - connected http_version='HTTP/2'
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - send_headers stream_id=1 method='GET' target='/' headers=[(b':method', b'GET'), (b':authority', b'google.com'), (b':scheme', b'https'), (b':path', b'/'), (b'user-agent', b'python-httpx/0.7.6'), (b'accept', b'*/*'), (b'accept-encoding', b'gzip, deflate, br'), (b'connection', b'keep-alive')]
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - end_stream stream_id=1
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<RemoteSettingsChanged changed_settings:{ChangedSetting(setting=SettingCodes.MAX_CONCURRENT_STREAMS, original_value=None, new_value=100), ChangedSetting(setting=SettingCodes.INITIAL_WINDOW_SIZE, original_value=65535, new_value=1048576), ChangedSetting(setting=SettingCodes.MAX_HEADER_LIST_SIZE, original_value=None, new_value=16384)}>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<WindowUpdated stream_id:0, delta:983041>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<SettingsAcknowledged changed_settings:{}>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=1 event=<ResponseReceived stream_id:1, headers:[(b':status', b'301'), (b'location', b'https://www.google.com/'), (b'content-type', b'text/html; charset=UTF-8'), (b'date', b'Wed, 06 Nov 2019 18:18:56 GMT'), (b'expires', b'Fri, 06 Dec 2019 18:18:56 GMT'), (b'cache-control', b'public, max-age=2592000'), (b'server', b'gws'), (b'content-length', b'220'), (b'x-xss-protection', b'0'), (b'x-frame-options', b'SAMEORIGIN'), (b'alt-svc', b'quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000')]>
DEBUG [2019-11-06 19:18:56] httpx._client - HTTP Request: GET https://google.com "HTTP/2 301 Moved Permanently"
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection_pool - acquire_connection origin=Origin(scheme='https' host='www.google.com' port=443)
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection_pool - new_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.google.com' port=443))
TRACE [2019-11-06 19:18:56] httpx._config - load_ssl_context verify=True cert=None trust_env=True http_versions=HTTPVersionConfig(['HTTP/1.1', 'HTTP/2'])
TRACE [2019-11-06 19:18:56] httpx._config - load_verify_locations cafile=/Users/florimond/Developer/python-projects/httpx/venv/lib/python3.8/site-packages/certifi/cacert.pem
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection - start_connect host='www.google.com' port=443 timeout=Timeout(timeout=5.0)
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection - connected http_version='HTTP/2'
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - send_headers stream_id=1 method='GET' target='/' headers=[(b':method', b'GET'), (b':authority', b'www.google.com'), (b':scheme', b'https'), (b':path', b'/'), (b'user-agent', b'python-httpx/0.7.6'), (b'accept', b'*/*'), (b'accept-encoding', b'gzip, deflate, br'), (b'connection', b'keep-alive')]
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - end_stream stream_id=1
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<RemoteSettingsChanged changed_settings:{ChangedSetting(setting=SettingCodes.MAX_CONCURRENT_STREAMS, original_value=None, new_value=100), ChangedSetting(setting=SettingCodes.INITIAL_WINDOW_SIZE, original_value=65535, new_value=1048576), ChangedSetting(setting=SettingCodes.MAX_HEADER_LIST_SIZE, original_value=None, new_value=16384)}>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<WindowUpdated stream_id:0, delta:983041>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<SettingsAcknowledged changed_settings:{}>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=1 event=<ResponseReceived stream_id:1, headers:[(b':status', b'200'), (b'date', b'Wed, 06 Nov 2019 18:18:56 GMT'), (b'expires', b'-1'), (b'cache-control', b'private, max-age=0'), (b'content-type', b'text/html; charset=ISO-8859-1'), (b'p3p', b'CP="This is not a P3P policy! See g.co/p3phelp for more info."'), (b'content-encoding', b'gzip'), (b'server', b'gws'), (b'content-length', b'5073'), (b'x-xss-protection', b'0'), (b'x-frame-options', b'SAMEORIGIN'), (b'set-cookie', b'1P_JAR=2019-11-06-18; expires=Fri, 06-Dec-2019 18:18:56 GMT; path=/; domain=.google.com; SameSite=none'), (b'set-cookie', b'NID=190=m8G9qLxCz2_4HbZI02ON2HTJF4xTvOhoJiS57Hm-OJrNS2eY20LfXMR_u-mLjujeshW5-BTezI69OGpHksT4ZK2TCDsWeU0DF7AmDTjjXFOdj30eIUTpNq7r9aWRvI8UrqiwlIsLkE8Ee3t5PiIiVdSMUcji7dkavGlMUpkMXU8; expires=Thu, 07-May-2020 18:18:56 GMT; path=/; domain=.google.com; HttpOnly'), (b'alt-svc', b'quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000')]>
DEBUG [2019-11-06 19:18:56] httpx._client - HTTP Request: GET https://www.google.com/ "HTTP/2 200 OK"
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=1 event=<DataReceived stream_id:1, flow_controlled_length:5186, data:1f8b08000000000002ffc55af97adb4692ff3f4f>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=1 event=<DataReceived stream_id:1, flow_controlled_length:221, data:>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=1 event=<StreamEnded stream_id:1>
TRACE [2019-11-06 19:18:56] httpx._dispatch.http2 - receive_event stream_id=0 event=<PingReceived ping_data:0000000000000000>
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection_pool - release_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.google.com' port=443))
TRACE [2019-11-06 19:18:56] httpx._dispatch.connection - close_connection

SSLKEYLOGFILE

Valid values: a filename

If this environment variable is set, TLS keys will be appended to the specified file, creating it if it doesn't exist, whenever key material is generated or received. The keylog file is designed for debugging purposes only.

Support for SSLKEYLOGFILE requires Python 3.8 and OpenSSL 1.1.1 or newer.

Example:

# test_script.py
import httpx

with httpx.AsyncClient() as client:
    r = client.get("https://google.com")
SSLKEYLOGFILE=test.log python test_script.py
cat test.log
# TLS secrets log file, generated by OpenSSL / Python
SERVER_HANDSHAKE_TRAFFIC_SECRET XXXX
EXPORTER_SECRET XXXX
SERVER_TRAFFIC_SECRET_0 XXXX
CLIENT_HANDSHAKE_TRAFFIC_SECRET XXXX
CLIENT_TRAFFIC_SECRET_0 XXXX
SERVER_HANDSHAKE_TRAFFIC_SECRET XXXX
EXPORTER_SECRET XXXX
SERVER_TRAFFIC_SECRET_0 XXXX
CLIENT_HANDSHAKE_TRAFFIC_SECRET XXXX
CLIENT_TRAFFIC_SECRET_0 XXXX

SSL_CERT_FILE

Valid values: a filename

if this environment variable is set then HTTPX will load CA certificate from the specified file instead of the default location.

Example:

SSL_CERT_FILE=/path/to/ca-certs/ca-bundle.crt python -c "import httpx; httpx.get('https://example.com')"

SSL_CERT_DIR

Valid values: a directory

if this environment variable is set then HTTPX will load CA certificates from the specified location instead of the default location.

Example:

SSL_CERT_DIR=/path/to/ca-certs/ python -c "import httpx; httpx.get('https://example.com')"

Proxies

The environment variables documented below are used as a convention by various HTTP tooling, including:

For more information on using proxies in HTTPX, see HTTP Proxying.

HTTP_PROXY, HTTPS_PROXY, ALL_PROXY

Valid values: A URL to a proxy

HTTP_PROXY, HTTPS_PROXY, ALL_PROXY set the proxy to be used for http, https, or all requests respectively.

export HTTP_PROXY=http://my-external-proxy.com:1234

# This request will be sent through the proxy
python -c "import httpx; httpx.get('http://example.com')"

# This request will be sent directly, as we set `trust_env=False`
python -c "import httpx; httpx.get('http://example.com', trust_env=False)"

NO_PROXY

Valid values: a comma-separated list of hostnames/urls

NO_PROXY disables the proxy for specific urls

export HTTP_PROXY=http://my-external-proxy.com:1234
export NO_PROXY=http://127.0.0.1,python-httpx.org

# As in the previous example, this request will be sent through the proxy
python -c "import httpx; httpx.get('http://example.com')"

# These requests will be sent directly, bypassing the proxy
python -c "import httpx; httpx.get('http://127.0.0.1:5000/my-api')"
python -c "import httpx; httpx.get('https://www.python-httpx.org')"