Error in Python trying to create a list of a certain length after a call to Fortran to get the length

I have a piece of Python code which needs to call Fortran to get the length of a list Python needs to create (so that it can pass that list of the correct size back to Fortran later).

Here is the code:

# get size of x
n = ct.c_int(0)
fs(ct.byref(n)) # fs is a Fortran subroutine which returns the length
print('n: ',n)
x = [0]*n
print('x: ',x)

However Python complains:

    x = [0]*n
TypeError: can't multiply sequence by non-int of type 'c_long'

If I change the initialization of n to n=0, the byref call on the next line fails with:

    fs(ct.byref(n))
TypeError: byref() argument must be a ctypes instance, not 'int'

How do I create a list of length n (obtained from Fortran)?

>Solution :

You can try explicit conversion of this type to int x = [0]*int(n)

if that doesn’t work, try x = [0]*n.value, refer: How to convert ctypes' c_long to Python's int?