Pandas conditionally copying of cell value

Question

Working with a Pandas DataFrame, I am trying to copy data from one cell into another cell only if the recipient cell contains a specific value. The transfer should go from:

   Col1    Col2
0     4       X
1     2       5
2     1       X
3     7       8
4    12      20
5     3       X

And the result should be

   Col1    Col2
0     4       4
1     2       5
2     1       1
3     7       8
4    12      20
5     3       3

Is there an elegant or simple solution I am missing?

Answer 1

df.Col2 = df.Col1.where(df.Col2 == 'X', df.Col2)

Answer 2

import pandas as pd
import numpy as np

df.Col2 = np.where(df.Col2 == 'specific value', df.Col1, df.Col2)