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Comment by user5994461 | Hacker News Reader

One liner to count gc, without buffering.

    import io
    f = io.StringIO(
    """
    AB
    CD
    EF
    GH
    """
    )

    total = sum(map(lambda s: 0 if s[0]==">" else s.count('G') + s.count('C'), f.readlines()))

    print(total)

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And reading the file as binary. There's a lesson about the overhead of unicode strings here ;)

Your first example takes 3.1 seconds, my previous comment takes 2.3 seconds, this one takes 1.4 seconds.

    start = time.perf_counter()

    with open("orthocoronavirinae.fasta", "rb") as f:
    total = sum(map(lambda s: 0 if s[0]==65 else s.count(b"G") + s.count(b"C"), f.readlines()))
    
    end = time.perf_counter()
    
    print(total, " total")
    print(end-start, " seconds")

This is good too. I would use a generator expression instead of the map though probably.

map is a generator

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