title: why AssertionError having numpy.ndarray
body: <p>My data frame is look like -</p>
  <pre><code>             can    sbi      bjf    srt      acc    amb     tata     jsw    hdfcl   sbil
  Date                                        
  2018-02-07  248.65  259.10  2298.40 1284.65 1313.75 200.30  560.95  313.25  457.65  667.90
  2018-03-07  244.70  257.75  2321.50 1298.45 1336.80 200.85  566.50  311.80  459.65  669.90
  2018-04-07  244.75  257.50  2331.95 1144.85 1352.65 201.15  568.90  312.00  459.60  664.60
  2018-05-07  243.75  256.60  2329.45 1151.90 1388.95 207.30  553.50  310.40  462.05  663.15
  2018-06-07  247.80  257.45  2341.70 1110.55 1373.45 207.35  554.15  309.30  468.90  667.40
  2018-09-07  249.55  261.35  2346.60 1139.95 1375.90 206.40  556.85  312.95  474.30  664.90
  2018-10-07  250.75  263.50  2366.30 1206.35 1371.50 204.10  568.60  316.75  476.70  660.00
  2018-11-07  244.15  258.90  2355.20 1205.80 1360.70 202.45  555.85  312.65  469.05  660.95
  2018-12-07  241.40  262.75  2414.30 1214.00 1349.15 202.05  556.30  316.80  478.00  664.35
  2018-07-13  231.95  257.60  2460.35 1253.55 1335.95 197.15  558.15  316.75  471.70  660.45
  </code></pre>
  <p>I want to do some EDA based on this data frame. My code is given below -</p>
  <pre><code>import numpy as np
  import pandas as pd
  # import pandas_datareader.data as web
  import matplotlib.pyplot as plt
  import statsmodels.regression.linear_model as rg
  import arch.unitroot as at
  import mxnet as mx
  
  data = pd.read_csv('/Users/XXXX/Downloads/Pairs-Trading-Analysis-Data.csv', index_col='Date', parse_dates=True)
  data.head(10)
  
  int1 = data.loc[:, ['bjf', 'srt']]
  tint1 = int1[:'2018-12-31']
  tint1.columns = ['taus', 'tcan']
  fint1 = int1['2019-01-02':]
  fint1.columns = ['faus', 'fcan']
  </code></pre>
  <p>Now I got this error -</p>
  <pre><code>---------------------------------------------------------------------------
  AssertionError                            Traceback (most recent call last)
  &lt;ipython-input-30-b374f43b65a9&gt; in &lt;module&gt;
        1 # 2.2. Training and Testing Ranges Delimiting
  ----&gt; 2 tint1 = int1[:'2018-12-31']
        3 tint1.columns = ['taus', 'tcan']
        4 fint1 = int1['2019-01-02':]
        5 fint1.columns = ['faus', 'fcan']
  
  ~/opt/anaconda3/lib/python3.8/site-packages/pandas/core/frame.py in __getitem__(self, key)
     2880             # either we have a slice or we have a string that can be converted
     2881             #  to a slice for partial-string date indexing
  -&gt; 2882             return self._slice(indexer, axis=0)
     2883 
     2884         # Do we have a (boolean) DataFrame?
  
  ~/opt/anaconda3/lib/python3.8/site-packages/pandas/core/generic.py in _slice(self, slobj, axis)
     3546         Slicing with this method is *always* positional.
     3547         &quot;&quot;&quot;
  -&gt; 3548         assert isinstance(slobj, slice), type(slobj)
     3549         axis = self._get_block_manager_axis(axis)
     3550         result = self._constructor(self._mgr.get_slice(slobj, axis=axis))
  
  AssertionError: &lt;class 'numpy.ndarray'&gt;
  </code></pre>
  <p>But the main thing is when I am using windows I am not getting any error but this error comes when I am using MAC os. Any specific reason for that?
  how to rectify this error?</p>