linear & slinear interpolation of constant data

slinear vs linear

pandas slinear: [60.0, 60.0, 60.0, 60.0, 59.999999999999993, 60.0, 60.0, 60.0]
pandas linear:  [60.0, 60.0, 60.0, 60.0, 60.0, 60.0, 60.0, 60.0]
scipy slinear: [60.0, 60.0, 60.0, 60.0, 59.999999999999993, 60.0, 60.0, 60.0]
scipy linear:  [60.0, 60.0, 60.0, 60.0, 60.0, 60.0, 60.0, 60.0]
F
======================================================================
FAIL: Proof that linear and slinear are not equal.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "....", line 329, in test_slinear_versus_linear
    self.assertEqual(scipy_y_slinear, scipy_y_linear)
AssertionError: Lists differ: [60.0, 60.0, 60.0, 60.0, 59.99... != [60.0, 60.0, 60.0, 60.0, 60.0,...

First differing element 4:
60.0
60.0

- [60.0, 60.0, 60.0, 60.0, 59.999999999999993, 60.0, 60.0, 60.0]
?                          --------------------

+ [60.0, 60.0, 60.0, 60.0, 60.0, 60.0, 60.0, 60.0]
?                                      ++++++

test_interp.py

from datetime import datetime
import unittest

from numpy import nan
from pandas import Series, date_range
from scipy import interpolate


class Tests(unittest.TestCase):
  
    def test_slinear_versus_linear(self):
          """Proof that linear and slinear are not equal."""
          data = [
              (27 * 60 + 13, 60), (42 * 60 + 15, 60),
              (57 * 60 + 17, 60), (60 * 60 + 12 * 60 +13, 60),
              (60 * 60 + 27 * 60 + 15, 60), (60 * 60 + 60 * 42 + 15, 60),
          ]

          s1 = Series(
              data=[x for y, x in data],
              index=[y for y, x in data]
          )
          empties = [30 * 60 * i for i in range(1, 3)]
          s2 = s1.reindex(s1.index | empties)
          x = s1.index
          y = s1.values

          pandas_y_linear = list(s2.interpolate(method='linear').values)
          pandas_y_slinear = list(s2.interpolate(method='slinear').values)
          scipy_y_linear = list(
              interpolate.interp1d(x, y, kind='linear')(s2.index)
          )
          scipy_y_slinear = list(
              interpolate.interp1d(x, y, kind='slinear')(s2.index)
          )
          print "pandas slinear:", pandas_y_slinear
          print "pandas linear: ", pandas_y_linear
          print "scipy slinear:", scipy_y_slinear
          print "scipy linear: ", scipy_y_linear

          self.assertEqual(scipy_y_slinear, scipy_y_linear)
          self.assertEqual(pandas_y_slinear, pandas_y_linear)