Hi,
For updating global variables, you need to use Dataiku Public API. See example below:
import dataiku
client = dataiku.api_client()
global_variables = client.get_variables()
print(global_variables)
global_variables["foo"] = "bar"
client.set_variables(global_variables)
print(global_variables)
The full documentation is located here for your reference: https://doc.dataiku.com/dss/latest/python-api/rest-api-client/client.html#dataikuapi.dssclient.DSSClient.get_variables
[EDIT] The answer above only works if your user has an ADMIN role on Dataiku. Otherwise, you can use the following code to edit the variable of one project from another:
import dataiku
client = dataiku.api_client()
project = client.get_project("TSFORECAST")
my_other_project_variables = project.get_variables()
print(my_other_project_variables)
my_other_project_variables["standard"]["foo"] = "bar"
project.set_variables(my_other_project_variables)
print(my_other_project_variables)
Hope it helps,
Alex