[Python-Dev] io.BufferedReader.peek() Behaviour in python3.1 (original) (raw)

MRAB python at mrabarnett.plus.com
Tue Jun 16 13:14:45 CEST 2009

Cameron Simpson wrote:

On 16Jun2009 02:18, MRAB <python at mrabarnett.plus.com> wrote:

My itch is that peek() feels like it should be "look into the buffer" but actually can block and/or change the buffer.

Can block, but not if you don't want it too. You might just want to see what, if anything, is currently available, up to n bytes. Am I missing something? In the face of an empty buffer (which I can't tell from outside) how do I prevent peek() blocking? More generally, if I go peek(n) and if n > bytesinbufferrightnow and the raw stream would block if a raw read is done? My concerns would go away if I could probe the buffer content size; then I could ensure peek(n) chose n <= the content size. If that's not enough, my problem - I can choose to read-and-block or go away and come back later.

I was thinking along the lines of:

 def peek(self, size=None, block=True)

If 'block' is True then return 'size' bytes, unless the end of the file/stream is reached; if 'block' is False then return up to 'size' bytes, without blocking. The blocking form might impose a limit to how much can be peeked (the maximum size of the buffer), or it might enlarge the buffer as necessary.

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