Method expects argument of type 'double *'? - python
I'm new to python and I'm trying to write some code using python wrappers for epanet which I believe are SWIG-wrapped. There is a method I need to use, as outlined below from the source. However I can't seem to get the method to accept any type of value for the 3rd argument "values:".. Anything I try I get the error: TypeError: in method 'ptrn_set', argument 3 of type 'double *'
How do I convert my value/values to 'double *' within Python? what is the solution?
Thankful for any help...
"""
ptrn_set(ph, index, values, len) -> int
Parameters
----------
ph: Handle
index: int
values: double *
len: int
"""
return _toolkit.ptrn_set(ph, index, values, len)
I found this here:
https://docs.python.org/2.4/lib/typesnumeric.html:
Floating point numbers are implemented using double in C
Did you try float?
Python itself does not support values of type double *. In C, that is a pointer-to-a-double-precision-floating-point-number. In Python, effectively every name is a pointer, but you can't have a (native) value that is a pointer.
From context, it looks like they actually want an array of doubles. They really ought to write that as double [], but double * is compatible with it. You could try
values = [1.0, 2.0]
_toolkit.ptrn_set(ph, index, values, len(values))
It's not very Pythonic to do that, but if it works, it works. If that doesn't work, see if your expanet python wrappers provide a way of constructing such values.
If your expanet Python wrappers don't provide a way to construct such values, you can try the cffi library, but it's quite tricky. I think x = ffi.new("double[10]") will give you an array of 10 doubles.
I know some time passed an you probably already solved it, but it might be useful for someone else.
you can use the following function to create an array that will be accepted by epanet:
def make_array(values):
dbl_arr = en.doubleArray(len(values))
for i in range(len(values)):
dbl_arr[i] = values[i]
return dbl_arr
the input is an array of float, like [1.2 , 0.8].
This assuming you imported the epanet python library as
from epanet import toolkit as en,
source: https://github.com/OpenWaterAnalytics/epanet-python/issues/57
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