Environment Variables and .ini File Settings

Pyramid behavior can be configured through a combination of operating system environment variables and .ini configuration file application section settings. The meaning of the environment variables and the configuration file settings overlap.


Where a configuration file setting exists with the same meaning as an environment variable, and both are present at application startup time, the environment variable setting takes precedence.

The term “configuration file setting name” refers to a key in the .ini configuration for your application. The configuration file setting names documented in this chapter are reserved for Pyramid use. You should not use them to indicate application-specific configuration settings.

Reloading Templates

When this value is true, templates are automatically reloaded whenever they are modified without restarting the application, so you can see changes to templates take effect immediately during development. This flag is meaningful to Chameleon and Mako templates, as well as most third-party template rendering extensions.

Environment Variable Name Config File Setting Name

Reloading Assets

Don’t cache any asset file data when this value is true. See also Overriding Assets.

Environment Variable Name Config File Setting Name


For backwards compatibility purposes, aliases can be used for configurating asset reloading: PYRAMID_RELOAD_RESOURCES (envvar) and reload_resources (config file).

Debugging Authorization

Print view authorization failure and success information to stderr when this value is true. See also Debugging View Authorization Failures.

Environment Variable Name Config File Setting Name

Debugging Not Found Errors

Print view-related NotFound debug messages to stderr when this value is true. See also NotFound Errors.

Environment Variable Name Config File Setting Name

Debugging Route Matching

Print debugging messages related to url dispatch route matching when this value is true. See also Debugging Route Matching.

Environment Variable Name Config File Setting Name

Debugging All

Turns on all debug* settings.

Environment Variable Name Config File Setting Name

Reloading All

Turns on all reload* settings.

Environment Variable Name Config File Setting Name

Default Locale Name

The value supplied here is used as the default locale name when a locale negotiator is not registered. See also Localization-Related Deployment Settings.

Environment Variable Name Config File Setting Name

Mako Template Render Settings

Mako derives additional settings to configure its template renderer that should be set when using it. Many of these settings are optional and only need to be set if they should be different from the default. The Mako Template Renderer uses a subclass of Mako’s template lookup and accepts several arguments to configure it.

Mako Directories

The value(s) supplied here are passed in as the template directories. They should be in asset specification format, for example: my.package:templates.

Config File Setting Name

Mako Module Directory

The value supplied here tells Mako where to store compiled Mako templates. If omitted, compiled templates will be stored in memory. This value should be an absolute path, for example: %(here)s/data/templates would use a directory called data/templates in the same parent directory as the INI file.

Config File Setting Name

Mako Input Encoding

The encoding that Mako templates are assumed to have. By default this is set to utf-8. If you wish to use a different template encoding, this value should be changed accordingly.

Config File Setting Name

Mako Error Handler

Python callable which is called whenever Mako compile or runtime exceptions occur. The callable is passed the current context as well as the exception. If the callable returns True, the exception is considered to be handled, else it is re-raised after the function completes. Is used to provide custom error-rendering functions.

Config File Setting Name

Mako Default Filters

List of string filter names that will be applied to all Mako expressions.

Config File Setting Name

Mako Import

String list of Python statements, typically individual “import” lines, which will be placed into the module level preamble of all generated Python modules.

Config File Setting Name

Mako Strict Undefined

true or false, representing the “strict undefined” behavior of Mako (see Mako Context Variables). By default, this is false.

Config File Setting Name


Let’s presume your configuration file is named MyProject.ini, and there is a section representing your application named [app:main] within the file that represents your Pyramid application. The configuration file settings documented in the above “Config File Setting Name” column would go in the [app:main] section. Here’s an example of such a section:

use = egg:MyProject#app
reload_templates = true
debug_authorization = true

You can also use environment variables to accomplish the same purpose for settings documented as such. For example, you might start your Pyramid application using the following command line:

       bin/paster serve MyProject.ini

If you started your application this way, your Pyramid application would behave in the same manner as if you had placed the respective settings in the [app:main] section of your application’s .ini file.

If you want to turn all debug settings (every setting that starts with debug_). on in one fell swoop, you can use PYRAMID_DEBUG_ALL=1 as an environment variable setting or you may use debug_all=true in the config file. Note that this does not affect settings that do not start with debug_* such as reload_templates.

If you want to turn all reload settings (every setting that starts with reload_). on in one fell swoop, you can use PYRAMID_RELOAD_ALL=1 as an environment variable setting or you may use reload_all=true in the config file. Note that this does not affect settings that do not start with reload_* such as debug_notfound.


Specifying configuration settings via environment variables is generally most useful during development, where you may wish to augment or override the more permanent settings in the configuration file. This is useful because many of the reload and debug settings may have performance or security (i.e., disclosure) implications that make them undesirable in a production environment.

Understanding the Distinction Between reload_templates and reload_assets

The difference between reload_assets and reload_templates is a bit subtle. Templates are themselves also treated by Pyramid as asset files (along with other static files), so the distinction can be confusing. It’s helpful to read Overriding Assets for some context about assets in general.

When reload_templates is true, Pyramid takes advantage of the underlying templating systems’ ability to check for file modifications to an individual template file. When reload_templates is true but reload_assets is not true, the template filename returned by the pkg_resources package (used under the hood by asset resolution) is cached by Pyramid on the first request. Subsequent requests for the same template file will return a cached template filename. The underlying templating system checks for modifications to this particular file for every request. Setting reload_templates to True doesn’t affect performance dramatically (although it should still not be used in production because it has some effect).

However, when reload_assets is true, Pyramid will not cache the template filename, meaning you can see the effect of changing the content of an overridden asset directory for templates without restarting the server after every change. Subsequent requests for the same template file may return different filenames based on the current state of overridden asset directories. Setting reload_assets to True affects performance dramatically, slowing things down by an order of magnitude for each template rendering. However, it’s convenient to enable when moving files around in overridden asset directories. reload_assets makes the system very slow when templates are in use. Never set reload_assets to True on a production system.