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]

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

[andy-slac]

Sorry for late followup question, could not find answer anywhere. I'm trying to do the same as original poster - pass parameters to make template. I tried to use config in the template as the answer suggests but I'm getting an exception NameError: name 'config' is not defined. From what I see is that config is only defined by default when autogenerate is enabled. I also see the option revision_environment - do I need to set it to true to have config defined? I guess I also need to pass sql=True to revision()?

[zzzeek]

looking at the source code it seems "config" is always in template_args unconditionally so make sure you are on a recent version of alembic and are using the command.revision command to do this render

[andy-slac]

Ah, my fault, sorry for the noise. My mistake was that I tried to use config inside <%! ... %> block. Works as you say in <% ... %>.