IronPython: Message: expected c_double, got c_double_Array_3

问题

I’m currently developing a script using the python script editor in Rhino. As I’m currently working in a Windows machine, the script editor uses IronPython as language.

In the same script, I want to interact with an FE software (Straus7) which has a Python API. When doing so, I have experienced some problems as the ctypes module does not seem to work in IronPython the same way it does in regular Python. Especially, I’m finding problems when initializing arrays using the command:

ctypes.c_double*3

For example, if I want to obtain the XYZ coordinates of a node #1 in the FE model, I regular Python I would write the following:

XYZType = ctypes.c_double*3
XYZ = XYZType()
node_num = 1
st.St7GetNodeXYZ(1,node_num,XYZ)

And this returns me a variable XYZ which is a 3D array such that:

XYZ -> <straus_userfunctions.c_double_Array_3 at 0xc5787b0>
XYZ[0] = -0.7xxxxx -> (X_coord)
XYZ[1] = -0.8xxxxx -> (Y_coord)
XYZ[2] = -0.9xxxxx -> (Z_coord)

On the other side, I copy the same exact script in IronPython, the following error message appears

Message: expected c_double, got c_double_Array_3

Obviously, If I change the variable XYZ to c_double; then it becomes a double variable which contains only a single entry, which corresponds to the first element of the array (in this case, the X-coordinate)

This situation is quite annoying as all FEM softwares, the usage of matrices and arrays is widely used. Consequently, I wanted to ask if anyone nows a simple fix to this situation.

I was thinking of using the memory allocation of the first element of the array to obtain the rest but I’m not so sure how to do so.

Thanks a lot. Gerard

回答1:

I've found when working with IronPython you need to explicitly cast the "Array of three doubles" to a "Pointer to double". So if you're using Grasshopper with the Strand7 / Straus7 API you will need to add an extra bit like this:

import St7API
import ctypes

# Make the pointer conversion functions
PI = ctypes.POINTER(ctypes.c_long)
PD = ctypes.POINTER(ctypes.c_double)

XYZType = ctypes.c_double*3
XYZ = XYZType()
node_num = 1

# Cast arrays whenever you pass them to St7API from IronPython
St7API.St7GetNodeXYZ(1, node_num, PD(XYZ))

I don't have access to IronPython or Strand7 / Straus7 at the moment but from memory that will do it. If that doesn't work for you you can email Strand7 Support - you would typically get feedback on something like this within a day or so.

来源：https://stackoverflow.com/questions/52097422/ironpython-message-expected-c-double-got-c-double-array-3

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python

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ironpython