Centurion incompatible with Py3

[bredeson]

Hi Devs,

I'm reporting this just in case you intend Centurion to be Py3-compatible.

I'm getting the following error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-19-152081d3bb39> in <module>
      1 centromeres = centromeres_calls.centromeres_calls(
      2     counts, lengths,
----> 3     resolution=10000)

~/.conda/envs/centurion/lib/python3.6/site-packages/centurion/centromeres_calls.py in centromeres_calls(counts, lengths, resolution, init, n_candidate, sigma, verbose, filter_candidates, normalize)
     21     if init is None:
     22         counts_40kb, lengths_40kb = utils.downsample_resolution(
---> 23             counts, lengths, coefficient=coef)
     24 
     25         if normalize:

~/.conda/envs/centurion/lib/python3.6/site-packages/centurion/utils.py in downsample_resolution(counts, lengths, coefficient)
     41             sub_target_counts = target_counts[target_begin_i:target_end_i,
     42                                               target_begin_j:target_end_j]
---> 43             for start in range(coefficient):
     44                 s = sub_counts[start::coefficient, start::coefficient]
     45                 sub_target_counts[:s.shape[0], :s.shape[1]] += s

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

because centromeres_calls.centromeres_calls() attempts division without flooring:

    if sigma is None:
        sigma = 80000 / resolution

    coef = 40000 / resolution

In Py3, division (even between two integers) yields a float, which could be avoided instead by using floor division (which returns an int):

    if sigma is None:
        sigma = 80000 // resolution

    coef = 40000 // resolution

In order to make Centurion Py3-compatible, floor division should be used everywhere an integer is expected to be returned.

Thanks!