import numpy as np
import pandas as pd

marks = [
    [90, 87],
    [90, 95],
    [92, 95]
]

marks

[[90, 87], [90, 95], [92, 95]]

df = pd.DataFrame(marks, columns=['maths', 'science'])

df

# reassign some values to nan

df['maths']

0    90
1    90
2    92
Name: maths, dtype: int64

df['maths'][0] = np.nan

df['maths']

0     NaN
1    90.0
2    92.0
Name: maths, dtype: float64

df = df.astype('int') # this will throw error

---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-27-b2504c49b1a1> in <module>()
----> 1 df = df.astype('int') # this will throw error


~/anaconda3/envs/py36/lib/python3.6/site-packages/pandas/core/generic.py in astype(self, dtype, copy, errors, **kwargs)
   5689             # else, only a single dtype is given
   5690             new_data = self._data.astype(dtype=dtype, copy=copy, errors=errors,
-> 5691                                          **kwargs)
   5692             return self._constructor(new_data).__finalize__(self)
   5693


~/anaconda3/envs/py36/lib/python3.6/site-packages/pandas/core/internals/managers.py in astype(self, dtype, **kwargs)
    529 
    530     def astype(self, dtype, **kwargs):
--> 531         return self.apply('astype', dtype=dtype, **kwargs)
    532 
    533     def convert(self, **kwargs):


~/anaconda3/envs/py36/lib/python3.6/site-packages/pandas/core/internals/managers.py in apply(self, f, axes, filter, do_integrity_check, consolidate, **kwargs)
    393                                             copy=align_copy)
    394 
--> 395             applied = getattr(b, f)(**kwargs)
    396             result_blocks = _extend_blocks(applied, result_blocks)
    397


~/anaconda3/envs/py36/lib/python3.6/site-packages/pandas/core/internals/blocks.py in astype(self, dtype, copy, errors, values, **kwargs)
    532     def astype(self, dtype, copy=False, errors='raise', values=None, **kwargs):
    533         return self._astype(dtype, copy=copy, errors=errors, values=values,
--> 534                             **kwargs)
    535 
    536     def _astype(self, dtype, copy=False, errors='raise', values=None,


~/anaconda3/envs/py36/lib/python3.6/site-packages/pandas/core/internals/blocks.py in _astype(self, dtype, copy, errors, values, **kwargs)
    631 
    632                     # _astype_nansafe works fine with 1-d only
--> 633                     values = astype_nansafe(values.ravel(), dtype, copy=True)
    634 
    635                 # TODO(extension)


~/anaconda3/envs/py36/lib/python3.6/site-packages/pandas/core/dtypes/cast.py in astype_nansafe(arr, dtype, copy, skipna)
    674 
    675         if not np.isfinite(arr).all():
--> 676             raise ValueError('Cannot convert non-finite values (NA or inf) to '
    677                              'integer')
    678


ValueError: Cannot convert non-finite values (NA or inf) to integer

df = df.fillna(0).astype('int') # this will throw error

df