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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def convert_all(folder, dest_path='.', force_all=False):
    "Convert modified notebooks in `folder` to html pages in `dest_path`."
    path = Path(folder)

    changed_cnt = 0
    for fname in path.glob("*.ipynb"):
        # only rebuild modified files
        fname_out = Path(dest_path)/fname.with_suffix('.html').name
        if not force_all and fname_out.exists():
            in_mod  = os.path.getmtime(fname)
            out_mod = os.path.getmtime(fname_out)
            if in_mod < out_mod: continue

        print(f"converting: {fname} => {fname_out}")
        changed_cnt += 1
        convert_nb(fname, dest_path=dest_path)
    if not changed_cnt: print("No notebooks were modified")