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API categories | API index

Application settings

Table of contents:

Introduction

These settings can be passed when calling cefpython.Initialize() .

The default values of options that are suggested in descriptions may not always be correct, it may be best to set them explicitily.

There are hundreds of options that can be set through CEF/Chromium command line switches. These switches can be set programmatically by passing a dictionary with switches as second argument to cefpython.Initialize(). See the CommandLineSwitches wiki page for more information.

Issue #244 is to add even more configurable settings by exposing API to Chromium Preferences.

Settings

accept_language_list

(string) Comma delimited ordered list of language codes without any whitespace that will be used in the "Accept-Language" HTTP header. May be overridden on a per-browser basis using the CefBrowserSettings.accept_language_list value. If both values are empty then "en-US,en" will be used. Can be overridden for individual CefRequestContext instances via the CefRequestContextSettings.accept_language_list value.

app_user_model_id

This is setting is applied only on Windows. It sets AppUserModelID (also known as AppID) for all processes (Browser, Renderer, GPU, etc.). Setting this is required on Windows 10 to workaround issues related to pinning app to Taskbar. More details can be found in Issue #395.

Internally this setting will append "--app-user-model-id" switch to all processes.

auto_zooming

(string) Windows only. Perform automatic zooming of browser contents. Example values for auto_zooming (numeric value means a zoom level):

  • "" - default is empty string
  • "0.0" (96 DPI)
  • "1.0" (120 DPI)
  • "2.0" (144 DPI)
  • "-1.0" (72 DPI)
  • "system_dpi" - Deprecated. Use system DPI settings. This value is deprecated, as it is no more required to set auto_zooming to this value after High DPI support was enabled.

Example values that can be set in Win7 DPI settings (Control Panel Appearance and Personalization Display):

  • Smaller 100% (Default) = 96 DPI = 0.0 zoom level
  • Medium 125% = 120 DPI = 1.0 zoom level
  • Larger 150% = 144 DPI = 2.0 zoom level
  • Custom 75% = 72 DPI = -1.0 zoom level

background_color

(int) Description from upstream CEF:

Background color used for the browser before a document is loaded and when no document color is specified. The alpha component must be either fully opaque (0xFF) or fully transparent (0x00). If the alpha component is fully opaque then the RGB components will be used as the background color. If the alpha component is fully transparent for a windowed browser then the default value of opaque white be used. If the alpha component is fully transparent for a windowless (off-screen) browser then transparent painting will be enabled.

32-bit ARGB color value, not premultiplied. The color components are always in a known order. Equivalent to the SkColor type in Chromium.

browser_subprocess_path

(string) The path to a separate executable that will be launched for sub-processes. If this value is empty on Windows or Linux then the main process executable will be used. If this value is empty on macOS then a helper executable must exist at "Contents/Frameworks/ Helper.app/Contents/MacOS/ Helper" in the top-level app bundle. See the comments on CefExecuteProcess() for details. Also configurable using the "browser-subprocess-path" command-line switch.

cache_path

(string) The location where cache data will be stored on disk. If empty then browsers will be created in "incognito mode" where in-memory caches are used for storage and no data is persisted to disk. HTML5 databases such as localStorage will only persist across sessions if a cache path is specified. Can be overridden for individual CefRequestContext instances via the CefRequestContextSettings.cache_path value.

CEF flushes cookies or other cache data to disk every 30 seconds, or immediately when cefpython.Shutdown() is called.

When this option is not set (empty string), a unique cache directory will be created in the user's temp directory for each run of the application.

command_line_args_disabled

(bool) Set to true (1) to disable configuration of browser process features using standard CEF and Chromium command-line arguments. Configuration can still be specified using CEF data structures or via the CefApp::OnBeforeCommandLineProcessing() method.

context_menu

(dict) Configure mouse context menu. All dict values are of type bool and are True by default.

  • enabled - whether to enable mouse context menu
  • navigation - show the "Back", "Forward" and "Reload" items. The "Reload" option calls Browser.ReloadIgnoreCache.
  • print - show the "Print..." item
  • view_source - show the "View source" item
  • external_browser - show the "Open in external browser" and "Open frame in external browser" options. On Linux the external browser is not focused when opening url.
  • devtools - show the "Developer Tools" option. See also ApplicationSettings.remote_debugging_port.

downloads_enabled

(bool) Default: True

Downloads are handled automatically. A default SaveAs file dialog provided by OS is displayed. See also the DownloadHandler wiki page.

external_message_pump

(bool) Default: False

This option is for use on Mac and Linux only. On Windows for best performance you should use a multi-threaded message loop instead of calling CefDoMessageLoopWork in a timer.

EXPERIMENTAL (Linux): There are issues with this option on Linux. See Issue #246 for details.

It is recommended to use this option as a replacement for calls to cefpython.MessageLoopWork(). CEF Python will do these calls automatically using CEF's OnScheduleMessagePumpWork. This results in improved performance on Windows and Mac and resolves some bugs with missing keyboard events on these platforms. See Issue #246 for more details.

IMPORTANT: Currently there are issues on Mac with both message loop work and external message pump. In Qt apps calling message loop work in a timer doesn't work anymore, you have to use external message pump. In wxPython apps it is required to call a message loop work in a timer and enable external message pump both at the same time (an incorrect approach, but it works). This is just a temporary solution and how this affects performance was not tested. See Issue #442 for more details.

Description from upstream CEF:

Set to true (1) to control browser process main (UI) thread message pump scheduling via the CefBrowserProcessHandler::OnScheduleMessagePumpWork() callback. This option is recommended for use in combination with the CefDoMessageLoopWork() function in cases where the CEF message loop must be integrated into an existing application message loop (see additional comments and warnings on CefDoMessageLoopWork). Enabling this option is not recommended for most users; leave this option disabled and use either the CefRunMessageLoop() function or multi_threaded_message_loop if possible.

framework_dir_path

The path to the CEF framework directory on macOS. If this value is empty then the framework must exist at "Contents/Frameworks/Chromium Embedded Framework.framework" in the top-level app bundle. Also configurable using the "framework-dir-path" command-line switch.

See also Issue #304.

ignore_certificate_errors

(bool) Set to true (1) to ignore errors related to invalid SSL certificates.
Enabling this setting can lead to potential security vulnerabilities like
"man in the middle" attacks. Applications that load content from the
internet should not enable this setting. Also configurable using the
"ignore-certificate-errors" command-line switch. Can be overridden for individual CefRequestContext instances via the CefRequestContextSettings.ignore_certificate_errors value.

IMPORTANT: This option not only ignores all certificate errors, but it also enables caching of content due to custom patch being applied (read more in "NOTE ON CACHING" further down). If you don't want this caching feature of insecure content then alternatively you can ignore certificate errors using the RequestHandler._OnCertificateError() callback. Note that disk caching is enabled only when the "cache_path" option is set.

NOTE ON CACHING: Chromium by default disallows caching of content when there is certificate error. There is a issue125.patch in the patches/ directory that can be enabled when doing a custom CEF build. This patch changes the caching behavior on sites with SSL certificate errors when used with this setting. This patch can be applied Chromium sources to allow for caching even when there is certificate error, but only when the "ignore_certificate_errors" option is set to True. When it's set to False then the Chromium's caching behavior does not change. Enabling caching with certificate errors is useful on local private networks that use self-signed SSL certificates. See the referenced CEF topic in Issue #125 for more details.

javascript_flags

(string) Custom flags that will be used when initializing the V8 Javascript engine.
The consequences of using custom flags may not be well tested. Also
configurable using the --js-flags switch.

To enable WebAssembly support set the --expose-wasm flag.

locale

(string) The locale string that will be passed to Webkit. If empty the default
locale of "en-US" will be used. This value is ignored on Linux where locale
is determined using environment variable parsing with the precedence order:
LANGUAGE, LC_ALL, LC_MESSAGES and LANG. Also configurable using the "lang"
command-line switch.

locales_dir_path

(string) The fully qualified path for the locales directory. If this value is empty
the locales directory must be located in the module directory. This value
is ignored on Mac OS X where pack files are always loaded from the app
bundle Resources directory. Also configurable using the "locales-dir-path"
command-line switch.

debug

(bool) Whether cefpython should display debug messages in console and write them to "log_file" (see the next option).

In previous versions of cefpython, this option was set by overwriting module's g_debug global variable, this way of setting is now deprecated.

log_file

(string) The directory and file name to use for the debug log. If empty a default log file name and location will be used. On Windows and Linux a "debug.log" file will be written in the main executable directory. On Mac OS X a "~/Library/Logs/_debug.log" file will be written where is the name of the main app executable. Also configurable using the "log-file" command-line switch.

log_severity

(int) The log severity. Only messages of this severity level or higher will be
logged. Also configurable using the --log-severity switch with
a value of "verbose", "info", "warning", "error", "error-report" or
"disable".

Accepted values - constants available in the cefpython module:

  • LOGSEVERITY_VERBOSE
  • LOGSEVERITY_INFO
  • LOGSEVERITY_WARNING
  • LOGSEVERITY_ERROR (default)
  • LOGSEVERITY_DISABLE

multi_threaded_message_loop

(bool) Set to true (1) to have the browser process message loop run in a separate thread. If false (0) than the cefpython.MessageLoopWork() function must be called from your application message loop. This option is only supported on Windows.

When this option is set to true, you don't call CEF message loop explicitilly anymore. Also app's main thread is no more CEF's UI thread, thus many of API calls will require using cef.cefpython.md#posttask function to run code on UI thread. You should also pay attention when reading API docs, as many handlers/callbacks execute on specific threads, so when this option is On then your app's code can start executing on different threads.

This option is not and cannot be supported on OS-X for architectural reasons.

net_security_expiration_enabled

(bool) Set to true (1) to enable date-based expiration of built in network security information (i.e. certificate transparency logs, HSTS preloading and pinning information). Enabling this option improves network security but may cause HTTPS load failures when using CEF binaries built more than 10 weeks in the past. See https://www.certificate-transparency.org/ and https://www.chromium.org/hsts for details. Can be set globally using the CefSettings.enable_net_security_expiration value.

pack_loading_disabled

(bool) Set to true (1) to disable loading of pack files for resources and locales.
A resource bundle handler must be provided for the browser and render
processes via CefApp::GetResourceBundleHandler() if loading of pack files
is disabled. Also configurable using the --disable-pack-loading switch.

persist_session_cookies

(bool) To persist session cookies (cookies without an expiry date or validity
interval) by default when using the global cookie manager set this value to
true. Session cookies are generally intended to be transient and most Web
browsers do not persist them. A |cache_path| value must also be specified to
enable this feature. Also configurable using the "persist-session-cookies"
command-line switch.

persist_user_preferences

(bool) To persist user preferences as a JSON file in the cache path directory set this value to true (1). A |cache_path| value must also be specified to enable this feature. Also configurable using the "persist-user-preferences" command-line switch. Can be overridden for individual CefRequestContext instances via the CefRequestContextSettings.persist_user_preferences value.

product_version

(string) Value that will be inserted as the product portion of the default
User-Agent string. If empty the Chromium product version will be used. If
|userAgent| is specified this value will be ignored. Also configurable
using the --product-version switch.

remote_debugging_port

(int) Set to a value between 1024 and 65535 to enable remote debugging on the
specified port. For example, if 8080 is specified the remote debugging URL
will be http://127.0.0.1:8080. CEF can be remotely debugged from CEF or
Chrome browser window. Also configurable using the "remote-debugging-port"
command-line switch.

A default value of 0 will generate a random port between 49152–65535. A value of -1 will disable remote debugging.

NOTE: Do not use the --remote-debugging-port command line switch, as it collides with this option.

resources_dir_path

(string) The fully qualified path for the resources directory. If this value is
empty the cef.pak and/or devtools_resources.pak files must be located in
the module directory on Windows/Linux or the app bundle Resources directory
on Mac OS X. Also configurable using the --resources-dir-path switch.

single_process

(bool) Set to true (1) to use a single process for the browser and renderer. This
run mode is not officially supported by Chromium and is less stable than
the multi-process default. Also configurable using the "single-process"
command-line switch.

string_encoding

(string) What kind of encoding should we use when converting unicode string to bytes string. This conversion is done when you pass a unicode string to javascript.

This encoding is also used when converting bytes to unicode, this includes the post data in the Request object.

The default is "utf-8".

The behavior for encode/decode errors is to replace the unknown character with "?", this can be changed in the "string_utils.pyx" file through UNICODE_ENCODE_ERRORS/BYTES_DECODE_ERRORS constants.

uncaught_exception_stack_size

(int) The number of stack trace frames to capture for uncaught exceptions.
Specify a positive value to enable the V8ContextHandler.OnUncaughtException() callback. Specify 0 (default value) and
OnUncaughtException() will not be called. Also configurable using the
"uncaught-exception-stack-size" command-line switch.

unique_request_context_per_browser

(bool) A request context provides request handling for a set of related browser
objects. Browser objects with different
request contexts will never be hosted in the same render process. Browser
objects with the same request context may or may not be hosted in the same
render process depending on the process model. Browser objects created
indirectly via the JavaScript window.open function or targeted links will
share the same render process and the same request context as the source
browser.

To successfully implement separate cookie manager per browser session
with the use of the RequestHandler.GetCookieManager callback, you have to
set unique_request_context_per_browser to True.

In upstream CEF each request context may have separate settings like cache_path, persist_session_cookies, persist_user_preferences, ignore_certificate_errors, enable_net_security_expiration, accept_language_list. Such functionality wasn't yet exposed in CEF Python.

user_agent

(string) Value that will be returned as the User-Agent HTTP header. If empty the default User-Agent string will be used. Also configurable using the "user-agent" command-line switch.

user_data_path

(string) The location where user data such as spell checking dictionary files will be stored on disk. If empty then the default platform-specific user data directory will be used ("~/.cef_user_data" directory on Linux, "~/Library/Application Support/CEF/User Data" directory on Mac OS X, "Local Settings\Application Data\CEF\User Data" directory under the user profile directory on Windows).

windowless_rendering_enabled

(bool) Set to true (1) to enable windowless (off-screen) rendering support. Do not enable this value if the application does not use windowless rendering as it may reduce rendering performance on some systems.