How to count the length of a fasta sequence and number of occurrence of a particular alphabet in the sequence from an input file?

Question

[d.kaur]

I have a list of protein sequences in a fasta file, where each entry has a header followed by the actual sequence and separated from the next entry with a new line. I want a script that reads the file that contains the sequences and outputs the length of each sequence and the number of times the alphabet A occurs in that sequence. I got the following script on Biostars from onuralp, which reads the file and gives me the length of each sequence. How can I modify the script for it to give me the number of 'A's in that sequence? Sequence length from Fasta

[Brice Sarver]

Is this a homework question?

[d.kaur]

No, I'm doing a project on the analysis of the amino acids in the proteins of interest.

Answer 1

[Mensur Dlakic]

You already have the ID and amino acid sequence extracted by this script. It is simply a matter of going through the sequence and increasing the counter each time a residue equals A. That would be 3-4 additional lines of code.