Application Globals ​

To share data that is valid for one request only from one function to another, a global variable is not good enough because it would break in threaded environments. Flask provides you with a special object that ensures it is only valid for the active request and that will return different values for each request. In a nutshell: it does the right thing, like it does for request and session.

flask.g ​

A namespace object that can store data during an application context. This is an instance of Flask.app_ctx_globals_class, which defaults to ctx._AppCtxGlobals.

This is a good place to store resources during a request. For example, a before_request function could load a user object from a session id, then set g.user to be used in the view function.

This is a proxy. See Notes On Proxies for more information.

class flask.ctx._AppCtxGlobals ​

A plain object. Used as a namespace for storing data during an application context.

Creating an app context automatically creates this object, which is made available as the g proxy.

• 'key' in g ​

  Check whether an attribute is present.

  Changelog

  New in version 0.10.

• iter(g) ​

  Return an iterator over the attribute names.

  Changelog

  New in version 0.10.

• get(name, default=None) ​

  Get an attribute by name, or a default value. Like dict.get().

  Parameters:

  • name (str) – Name of attribute to get.

  • default (Any | None) – Value to return if the attribute is not present.

  Return type: Any

  Changelog

  New in version 0.10.

• pop(name, default=<object object>) ​

  Get and remove an attribute by name. Like dict.pop().

  Parameters:

  • name (str) – Name of attribute to pop.

  • default (Any) – Value to return if the attribute is not present, instead of raising a KeyError.

  Return type: Any

  Changelog

  New in version 0.11.

• setdefault(name, default=None) ​

  Get the value of an attribute if it is present, otherwise set and return a default value. Like dict.setdefault().

  Parameters:

  name (str) – Name of attribute to get.

  default (Any | None) – Value to set and return if the attribute is not present.

  Return type: Any

  Changelog

  New in version 0.11.