Kompot exposes a serialization mechanism for Python builtins and Anvil portable classes.

Kompot provides wrappers for anvil.server.call() and @anvil.server.callable to take advantage of the enhanced serialization between client and server calls.

Wikipedia on kompot:

In 1885, Lucyna Ćwierczakiewiczowa wrote in a recipe book that kompot preserved fruit so well it seemed fresh


In addition to standard JSONable types, kompot supports the following builtins:

set, frozenset, tuple, date, datetime

dict objects will preserve their order and keys can be arbitrary.

type objects registered with kompot can also be serialized.



All portable classes that kompot can serialize must be registered by calling register(cls).

from anvil_labs import kompot
import anvil.server

class Foo:


(kompot.register can also be used as a decorator)


Serialize an arbitrary object into a JSONable object.

If kompot does not know how to handle the object, it will be left untouched.

Kompot does not know how to handle objects like:

  • anvil table rows

  • media objects

  • capabilities

We leave Anvil to serialize these objects when calling the server.


Like serialize but will throw a SerializationError if there are any unhandled objects.

Use preserve for storing an object as a simple object.

Use serialize for sending an object from the client to the server.


Reconstruct an object from the output of serialize or preserve

call(fn_name, *args, **kws)
call_s(fn_name, *args, **kws)
call_async(fn_name, *args, **kws)

Use inplace of anvil.server.call()

Kompot will serialize the args and kws and reconstruct the returned value.

The server function must be decorated with @kompot.callable.


Use inplace of @anvil.server.callable.

Kompot will reconstruct the serialized args and kws, call the original function and then serialize the return value.

Must be combined with kompot.call().


A context manager for batching calls

from anvil_labs import kompot

with kompot.batch_call(silent=True) as c:
    c.call("foo", x=1)
    c.call("bar", 42)

foo_result, bar_result = c.result