list operations in python

1. How to make each term of an array repeat, with the same terms grouped together?
   i/p:[A,B,C]
   o/p:[A,A,A,B,B,B,C,C,C]
   
   Solution:
   >>> l=['A','B','C']
   >>> [x for x in l for _ in range(3) ]
   ['A', 'A', 'A', 'B', 'B', 'B', 'C', 'C', 'C']
   
   [or]
   >>> import numpy as np
   >>> l=['A','B','C']
   >>> np.repeat(l,3).tolist()
   ['A', 'A', 'A', 'B', 'B', 'B', 'C', 'C', 'C']
   [or]
   
   

   >>> list(chain(*zip(*[l]*3)))
   ['A', 'A', 'A', 'B', 'B', 'B', 'C', 'C', 'C']

   
   
   
   
2. adding 1 constant value to all sub_list in a list in python
   >>> l=[[1,2],[3,4],[5,6]]
   Add one more element('one') to the sublist
   Solution:
   >>> l=[[1,2],[3,4],[5,6]]
   >>> [x+['one'] for x in l]
   [[1, 2, 'one'], [3, 4, 'one'], [5, 6, 'one']]
3. How do I remove all "nan" from the following list?
   

   mylist = [nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, n nan, 340000.0, 340050.0, 338003.0, 338004.0, 338005.0, 338006.0, 338008.0, 338010.0, 338011.0, 338018.0, 338019.0, nan, nan, nan, nan]

   Solution:

   mylist.remove(x) is a inplace operation and does return None always
   Instead you should be filtering it as follows
   >>> [x for x in mylist if not math.isnan(x)] [340000.0, 340050.0, 338003.0, 338004.0, 338005.0, 338006.0, 3380