Turning multiple excel arrays into two columns using python

Question

I have the following a series of columns and rows in Excel that look similar to the below (I'll mention that I have a significant number of columns and rows and this is a simplified example)

A  B  C  D
1  2  7  6
2  7  9
3     1
4     0
      1

I am looking for a python function that would take those columns and turn them into the following two columns:

A 1
A 2
A 3
A 4
B 2
B 7
C 7
C 9
C 1
C 0
C 1
D 6

Essentially, creating a separate row for each number under the first row and repeating the letter.

I have created a VBA function but unfortunately it is taking way too long.