# FILE: compute-average-fasta.py
# AUTHOR: William Stafford Noble
# CREATE DATE: 18 January 2007
# PROJECT: GENOME 559
import sys

# Make sure we got a filename on the command line.
if (len(sys.argv) != 2):
    print("USAGE: count-fasta.py <file>")
    sys.exit(1)

# Open the file for reading.
fasta_file = open(sys.argv[1], "r")

num_seqs = 0
total_chars = 0.0
for line in fasta_file:
    # Increment the sequence count or the character count.
    if (line[0] == ">"):
        num_seqs += 1
    else:
        # Error check: Make sure we don't have sequence before ID.
        if (num_seqs == 0):
            print("Invalid FASTA format.")
            sys.exit(1)
        # Subtract one for the end-of-line character.
        total_chars += len(line) - 1
print( total_chars / num_seqs)
fasta_file.close()