silence.py 文件源码

def __enter__(self):
        self.sys = sys
        # save previous stdout/stderr
        self.saved_streams = saved_streams = sys.__stdout__, sys.__stderr__
        self.fds = fds = [s.fileno() for s in saved_streams]
        self.saved_fds = map(os.dup, fds)
        # flush any pending output
        for s in saved_streams: s.flush()

        # open surrogate files
        if self.combine:
            null_streams = [open(self.outfiles[0], self.mode, 0)] * 2
            if self.outfiles[0] != os.devnull:
                # disable buffering so output is merged immediately
                sys.stdout, sys.stderr = map(os.fdopen, fds, ['w']*2, [0]*2)
        else: null_streams = [open(f, self.mode, 0) for f in self.outfiles]
        self.null_fds = null_fds = [s.fileno() for s in null_streams]
        self.null_streams = null_streams

        # overwrite file objects and low-level file descriptors
        map(os.dup2, null_fds, fds)