How to merge dataframe rows that have the same field?

Question

I have a dataframe in the following format:

  Col1  Col2
0   A  100  
1   A  25 
2   B  27  
3   C  35
4   C  10

How would I go about condensing it into this format:

  Col1  Col2
0   A  125  
2   B  27  
3   C  45