Deprecating non-integer arguments in special.perm with exact=True

Contributor & Development Discussion scipy
1

Hi all,

Currently the behaviour of perm with exact=True is inconsistent with the other combinatorial functions. Specifically, floats sometimes cause an error and sometimes produce an output:

In [4]: perm(4.6, 6, exact=True)
Out[4]: 0

In [5]: perm(4.6, 3, exact=True)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[5], line 1
----> 1 perm(4.6, 3, exact=True)

File ~/development/scipy/build-install/lib/python3.11/site-packages/scipy/special/_basic.py:2797, in perm(N, k, exact)
   2795     return 0
   2796 val = 1
-> 2797 for i in range(N - k + 1, N + 1):
   2798     val *= i
   2799 return val

TypeError: 'float' object cannot be interpreted as an integer

I have opened a PR to deprecate this behaviour; please feel free to discuss.

Jake

2

+1 for the deprecation :+1: