Compare custom column values and print difference in pandas DataFrame

Question

I have two DataFrames:

df1 = {\'MS\': [1000, 1005, 1007, NaN, 1010, 1012, 1020],
      \'Command\': [\'RD\', \'RD\', \'WR\', \'---\', \'RD\', \'RD\', \'WR\'],