Exercise $7\mathrm{.}1-$ Counting alphabetical letters$($Python$)$

Write a function that counts the number of letters in a string. Only count alphabetical letters. Then write a test code to take a String and print out the number of alphabetical letters in the string.

Sample output:

Enter a string: Test$123$ Test$123$

The number of letters in Test$123$ Test$123$ is: $8$