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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 get_filesystem(filename):
 """Return the registered filesystem for the given file."""

    filename = compat.as_str_any(filename)
    prefix = ""
    index = filename.find("://")
    if index >= 0:
        prefix = filename[:index]
    fs = _REGISTERED_FILESYSTEMS.get(prefix, None)
    if fs is None:
        raise ValueError("No recognized filesystem for prefix %s" % prefix)
    return fs