Complete the for loop and string method needed in this function so that a function call like "alpha_length("This has 1 number in it")" will return the output "17". This function should:

accept a string through the parameters of the function;

iterate over the characters in the string;

determine if each character is a letter (counting only alphabetic characters; numbers, punctuation, and spaces should be ignored);

increment the counter;

return the count of letters in the string.

def alpha_length(string):

character = ""

count_alpha = 0

# Complete the for loop sequence to iterate over "string".

for ___:

# Complete the if-statement using a string method.

if ___:

count_alpha += 1

return count_alpha

print(alpha_length("This has 1 number in it")) # Should print 17

print(alpha_length("Thisisallletters")) # Should print 16

print(alpha_length("This one has punctuation!")) # Should print 21