main.py

import textwrap

import timeitrunner

def old(fsrc, fdst, length=16*1024):
    """copy data from file-like object fsrc to file-like object fdst"""
    while 1:
        buf = fsrc.read(length)
        if not buf:
            break
        fdst.write(buf)


def new(fsrc, fdst, length=16*1024):
    """copy data from file-like object fsrc to file-like object fdst"""
    write = fdst.write
    if hasattr(fsrc, 'readinto') and length > 0:
        buf = memoryview(bytearray(length))
        readinto = fsrc.readinto
        while 1:
            recv_len = readinto(buf)
            if recv_len < length:
                # write remaining content if any.
                write(buf[:recv_len])
                break
            write(buf)
    else:
        read = fsrc.read
        while 1:
            buf = read(length)
            if not buf:
                break
            write(buf)

if __name__ == '__main__':
    setup = textwrap.dedent('''\
    import io
    
    a = io.BytesIO(bytearray([0] * {n} * 1024))
    
    from main import old, new
    ''')
    
    for kb, cycles in ((1, 2000), (1_000, 20), (10_000, 5)):
        print('    - {kb}kb (cycles={cycles})'.format(kb=kb, cycles=cycles))
        runner = timeitrunner.Runner(
            examples=(
                timeitrunner.Example(statement='b = io.BytesIO(); old(a, b)'),
                timeitrunner.Example(statement='b = io.BytesIO(); new(a, b)'),
            ),
            repeats=3,
            cycles=cycles,
            setup=setup.format(n=kb),
        )
        
        runner.run()
        print(runner.tabulate())

timeitrunner.py

import timeit

import attr


@attr.s(frozen=True)
class Example:
    statement = attr.ib()
    

@attr.s
class Runner:
    examples = attr.ib()
    setup = attr.ib(default='')
    repeats = attr.ib(default=3)
    cycles = attr.ib(default=1000)
    results = attr.ib(default=attr.Factory(dict))

    def run(self):
        for example in self.examples:
            self.results[example] = min(timeit.repeat(
                stmt=self.setup + '\n' + example.statement,
                repeat=self.repeats,
                number=self.cycles,
            ))

    def tabulate(self):
        minimum = min(self.results.values())
        lines = []
        for example in sorted(self.examples, key=lambda e: self.results[e]):
            lines.append('{percent:5}%   {statement}'.format(
                percent=round(100 * self.results[example] / minimum),
                statement=example.statement,
            ))
        
        return '\n'.join(lines)