[Python-Dev] Incorrect documentation of the raw_input built-in function (original) (raw)

Mike Kent mike.kent at sage.com
Thu Jan 24 16:33:47 CET 2008

Recently I was trying to debug an old python program who's maintenance I inherited. I was using the quick-and-dirty method of putting some 'print

sys.stderr' statements in the code, and then running the command with '2>filename' appended to the end of the command line. Imagine my surprise to see that all of the prompt text from the program's raw_input calls were also disappearing from the screen output, and appearing in the stderr output routed to the file.

The latest documentation for raw_input states "If the prompt argument is present, it is written to standard output without a trailing newline." I posted a question regarding the observed behavior to comp.lang.python and Gabriel Genellina (thanks Gabriel!) pointed out that despite the documentation, raw_input was hard-coded to always output its prompt text to stderr.

This raises two questions:

  1. Shouldn't the current documentation be corrected to state that raw_input writes its prompt to standard error?
  2. Is this really the hard-coded behavior we want? I don't think my use-case is that odd; in fact, what I find very odd is that the prompt output is send to stderr. I mean, I'm printing the prompt for a question, not some error message. Can there not at least be an optional parameter to indicate that you want the output sent to stdout rather than stderr?

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