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7888 :: In Nimpy how to call methods on Python objects? (Example sys.path.insert)

• halloleo (orginal) [2021-04-30T05:25:04+02:00] view original

  I stumbled over nimpy and I think it is a fantastic project! I'm now trying to use nimpy to call a locally given python module in Nim.

  The first thing I want to do is more basic: Modifying Python's sys.path. I though of doing this via the Python object in Nim. I have:

  
  import nimpy
  
  let sys = pyImport("sys")
  sys.path.insert(0, ".")
  Run

  However with this I get

  "Error: expression 'newPyObjectConsumingRef(callMethodAux(getAttr(sys, "path"), "insert", [nimValueToPy(0), nimValueToPy(".")], []))' is of type 'PyObject' and has to be used (or discarded)"

  So I assume the problem is: The Python object path can be accessed via the dot '.' from sys but then the Python method cannot be accessed via a further '.'.

  How can I call methods on Python objects?

  BTW, maybe I haven't found it yet, but is there beyond the README some API like doco for nimpy?

  PS: I am using Nim1.3.5 if that makes a difference here.

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• z_____________ (orginal) [2021-04-30T07:05:03+02:00] view original

  It works when you add discard:

  import nimpy
  
  let sys = pyImport("sys")
  discard sys.path.insert(0, ".")
  Run

  The problem with the original code is that Nim does not allow return values to be implicitly discarded.

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• chrisheller (orginal) [2021-04-30T07:47:26+02:00] view original

  Try

  
  discard sys.path.insert(0, ".")
  Run

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• xigoi (orginal) [2021-04-30T09:15:52+02:00] view original

  Indeed. The reason is that since Python is dynamically typed, Nim has no way to tell that the function always returns None, so it can't just allow you to silently throw away the result.

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• halloleo (orginal) [2021-04-30T15:37:30+02:00] view original

  Thanks for all the advice. Reactive programming I thought so, but was irritated that insert doesn’t have a return value. Thanks for the explanation to this

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