Pytket : TypeError: Parameters to generic types must be types. Got lark.visitors.Discard.

[hamidelmaazouz]

Hello @ss2165 and @cqc-alec,

I am getting the following failure when I call circuit_to_qasm_str from pytket.qasm:

[...]
from pytket.qasm import circuit_to_qasm_str
../../../.cache/pypoetry/virtualenvs/scc-uCUxejjC-py3.8/lib/python3.8/site-packages/pytket/qasm/__init__.py:19: in <module>
    from .qasm import (
../../../.cache/pypoetry/virtualenvs/scc-uCUxejjC-py3.8/lib/python3.8/site-packages/pytket/qasm/qasm.py:277: in <module>
    class CircuitTransformer(Transformer):
../../../.cache/pypoetry/virtualenvs/scc-uCUxejjC-py3.8/lib/python3.8/site-packages/pytket/qasm/qasm.py:759: in CircuitTransformer
    def extern(self, tree: List[Any]) -> Type[Discard]:
/usr/lib/python3.8/typing.py:261: in inner
    return func(*args, **kwds)
/usr/lib/python3.8/typing.py:685: in __getitem__
    params = tuple(_type_check(p, msg) for p in params)
/usr/lib/python3.8/typing.py:685: in <genexpr>
    params = tuple(_type_check(p, msg) for p in params)
/usr/lib/python3.8/typing.py:149: in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
E   TypeError: Parameters to generic types must be types. Got lark.visitors.Discard.

(I think) this would make sense on python 3.9+ but I have been experiencing this on both python 3.9 (using the prebuilt Pytket at https://pypi.org/project/pytket/) and python 3.8 (using the wheel I built myself as per the topic: #786)

For reference the failing method is:

    def extern(self, tree: List[Any]) -> Type[Discard]:
        # TODO parse extern defs
        return Discard

I'm not sure it should return Discard or Type[Discard], and the cause might be somewhere else.
Could you please shed some light on this ?

Best wishes,

[cqc-alec]

Hi, could you provide a code snippet to reproduce please?

[cqc-alec]

Or was the error just from the import?
I can't reproduce this with pytket 1.11.1:

(env) alec@psi:~/tmp$ python -c "from pytket.qasm import circuit_to_qasm_str"
(env) alec@psi:~/tmp$ 

[hamidelmaazouz]

No the import works fine, it's just the call that fails.

Turns out my project and Pytket are using different versions of Lark. Downgrading to Lark 0.12 made the failure go away.
Lark is now at 1.1.5, and Pytket pulls 0.7

Best,