util.py 文件源码

def _redirected_fd(to=os.devnull, stdio=None):
    if stdio is None:
        stdio = sys.stdout

    stdio_fd = _get_fileno(stdio)
    # copy stdio_fd before it is overwritten
    # NOTE: `copied` is inheritable on Windows when duplicating a standard
    # stream
    with os.fdopen(os.dup(stdio_fd), 'wb') as copied:
        stdio.flush()  # flush library buffers that dup2 knows nothing about
        try:
            os.dup2(_get_fileno(to), stdio_fd)  # $ exec >&to
        except ValueError:  # filename
            with open(to, 'wb') as to_file:
                os.dup2(to_file.fileno(), stdio_fd)  # $ exec > to
        try:
            yield stdio  # allow code to be run with the redirected stdio
        finally:
            # restore stdio to its previous value
            # NOTE: dup2 makes stdio_fd inheritable unconditionally
            stdio.flush()
            os.dup2(copied.fileno(), stdio_fd)  # $ exec >&copied