How does Python get the value for sys.stdin.encoding?

Thu Aug 12 07:50:43 CEST 2010

In article <mailman.1988.1281579897.1673.python-list at>,
 Benjamin Kaplan <benjamin.kaplan at> wrote:

> On Wed, Aug 11, 2010 at 6:21 PM, RG <rNOSPAMon at> wrote:
> > I thought it was hard-coded into the Python executable at compile time,
> > but that is apparently not the case:
> >
> > [ron at mickey:~]$ python
> > Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29)
> > [GCC 4.2.1 (Apple Inc. build 5646)] on darwin
> > Type "help", "copyright", "credits" or "license" for more information.
> >>>> import sys;print sys.stdin.encoding
> > UTF-8
> >>>> ^D
> > [ron at mickey:~]$ echo 'import sys;print sys.stdin.encoding' | python
> > None
> > [ron at mickey:~]$
> >
> > And indeed, trying to pipe unicode into Python doesn't work, even though
> > it works fine when Python runs interactively.  So how can I make this
> > work?
> >
> Sys.stdin and stdout are files, just like any other. There's nothing
> special about them at compile time. When the interpreter starts, it
> checks to see if they are ttys. If they are, then it tries to figure
> out the terminal's encoding based on the environment. The code for
> this is in pythonrun.c if you want to see exactly what it's doing.

Thanks.  Looks like the magic incantation is:


> By the way, there is no such thing as piping Unicode into Python.

Yeah, I know.  I should have said "piping UTF-8 encoded unicode" or 
something like that.

> You really have to watch your encodings
> when you pass data around between programs. There's no way to avoid
> it.

Yeah, I keep re-learning that lesson again and again.


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