Abstract

    Everybody agrees that mixing tabs and spaces is a bad idea.  Some
    people want more than this.  I propose that we let people define
    whatever Python behaviour they want, so it will only run the way
    they like it, and will not run the way they don't like it.  We
    will do this with a command line switch.  Programs that aren't
    formatted the way the programmer wants things will raise
    IndentationError:

    Python -TNone will refuse to run when there are any tabs.
    Python -Tn will refuse to run when tabs are not exactly n spaces
    Python -TOnly will refuse to run when blocks are indented by anything
            other than tabs

   People who mix tabs and spaces, naturally, will find that their
   programs do not run.  Alas, we haven't found a way to give them an
   electric shock as from a cattle prod remotely.  (Though if somebody
   finds out a way to do this, I will be pleased to add this option to
   the PEP.)

    

Rationale

   Python-list@python.org (a.k.a. comp.lang.python) is periodically
   awash with discussions about tabs and spaces.  This is inevitable,
   given that indentation is syntactically significant in Python.
   This has never solved anything, and just makes various people
   frustrated and angry.  Eventually they start saying rude things to
   each other which is sad for all of us.  And it is also sad that
   they are wasting their valuable time which they could spend
   creating something with Python.  Moreover, for the Python community
   as a whole, from a public relations point of view, this is quite
   unfortunate.  The people who aren't posting about tabs and spaces,
   are, (unsurprisingly) invisible, while the people who are posting
   make the rest of us look somewhat foolish.

   The problem is that there is no polite way to say 'Stop wasting
   your valuable time and mine.'  People who are already in the middle
   of a flame war are not well disposed to believe that you are acting
   out of compassion for them, and quite rightly insist that their own
   time is their own to do with as they please.  They are stuck like
   flies in treacle in this wretched argument, and it is self-evident
   that they cannot disengage or they would have already done so.

   But today I had to spend time cleaning my keyboard because the 'n'
   key is sticking.  So, in addition to feeling compassion for these
   people, I am pretty annoyed.  I figure if I make this PEP, we can
   then ask Guido to quickly reject it, and then when this argument
   next starts up again, we can say 'Guido isn't changing things to
   suit the tab-haters or the only-tabbers, so this conversation is a
   waste of time.'  Then everybody can quietly believe that a) they
   are correct and b) other people are fools and c) they are
   undeniably fortunate to not have to share a lab with idiots, (which
   is something the arguers could do _now_, but apparently have
   forgotten).

   And python-list can go back to worrying if it is too smug, rather
   than whether it is too hostile for newcomers.  Possibly somebody
   could get around to explaining to me what is the difference between
   __getattr__ and __getattribute__ in non-Classic classes in 2.2, a
   question I have foolishly posted in the middle of the current tab
   thread.  I would like to know the answer to that question.[2]
   
   This proposal, if accepted, will probably mean a heck of a lot of
   work for somebody.  But since I don't want it accepted, I don't
   care.

References

    [1] PEP 1, PEP Purpose and Guidelines
        http://www.python.org/dev/peps/pep-0001/

    [2] Tim Peters already has (private correspondence).  My early 2.2 
        didn't have a __getattribute__, and __getattr__ was
        implemented like __getattribute__ now is.  This has been
        fixed.  The important conclusion is that my Decorator Pattern
        is safe and all is right with the world.

Copyright

    This document has been placed in the public domain.