Code completion with param when a class implements the init method

Davide_sd · July 29, 2025, 5:54pm

I am implementing a class which requires the __init__ method to accept some arguments. The only issue is that by implementing it, I lose the code completion capability (at least in Jupyter Notebook, where I do have code completion turned on). Here is an example:

import param
class Test(param.Parameterized):
    first_param = param.Integer(default=2, doc="first")
    second_param = param.Dict(default={}, doc="second")
    third_param = param.Selector(default="a", objects=["a", "b", "c"], doc="third")

    def __init__(self, *args, **kwargs):
        super().__init__(**kwargs)

If you type Test(first_ in a new cell, no completion is shown. If you comment out the __init__ method, code completion works fine. Is there any way to fix this behavior?

maximlt · July 29, 2025, 8:10pm

That’s indeed the current behavior, i.e. overriding the default __init__ signature disables the automatic setting of the __signature__ class attribute that is leveraged by IPython for autocompletion:

github.com

holoviz/param/blob/a7f274269530209ce6e84355b45a5976bd88afd6/param/parameterized.py#L4399


      
          For classes with a constructor signature that matches the default
          Parameterized.__init__ signature (i.e. ``__init__(self, **params)``)
          this method will generate a new signature that expands the
          parameters. If the signature differs from the default the
          custom signature is returned.
          """
          if mcs._param__private.signature:
              return mcs._param__private.signature
          # allowed_signature must be the signature of Parameterized.__init__
          # Inspecting `mcs.__init__` instead of `mcs` to avoid a recursion error
          if inspect.signature(mcs.__init__) != DEFAULT_SIGNATURE:
              return None
          processed_kws, keyword_groups = set(), []
          for cls in reversed(mcs.mro()):
              keyword_group = []
              for k, v in sorted(cls.__dict__.items()):
                  if isinstance(v, Parameter) and k not in processed_kws and not v.readonly:
                      keyword_group.append(k)
                      processed_kws.add(k)
              keyword_groups.append(keyword_group)

That’s a conservative approach that I guess could be improved. Can you open an issue?

Davide_sd · July 29, 2025, 9:06pm

Thank you for pointing me in the right direction. I opened the issue here.

Code completion with param when a class implements the __init__ method

Code completion with param when a class implements the init method