Is it possible to pass variables into the script.py.mako file at revision generation time?

[ghost]

I'm working on a system where I have a few x_data behaviours, and I'd love to be able to express something like this:

# script.mako.py

def upgrade () -> None:
  if "switch" in context.get_x_argument():
    # do stuff conditional on switch
  else:
    # do other stuff

as

# script.mako.py

def upgrade () -> None:
% if some_object.arguments.switch:
  # do stuff
% else
  # do other stuff
% endif

Why? Because I'd like to generate the migrations that can then be run in other contexts without having to remember the particular values of the switches passed in at generation time. Yes, I could just copy & paste, but the template engine is right there, you know?

TIA!

[zzzeek]

sure, you can do whatever you want in the template.

some examples on doing more in the templates you can see for example at

alembic/alembic/templates/multidb/script.py.mako

Line 38 in 8829bd6

% for db_name in re.split(r',\s*', db_names):

[ghost]

Thanks! I guess my next question is, how do I carry that information from invocation time (alembic revision -m '...') to the generation of the migration itself? IOW, there are a bunch of context objects available in env.py, and a bunch of hooks, but which ones are available when the mako template is being processed?

[ghost]

And I figured it out. There's a dict on the Config object called "attributes" that I can use to pass stuff from env.py into the mako template. I did this:

# env.py

config.attributes["switch"] = "switch" in context.get_x_arguments()

<% 
switch = config.attributes.get("switch", False)
%>

% if switch:
# do stuff
% else:
# do other stuff
% endif

and this works great. Thanks for the pointer!

[zzzeek]

right, I knew there was something, thanks for figuring it out