Am 23.10.2011 20:33, schrieb Meador Inge:
> 
> Meador Inge <meadori@gmail.com> added the comment:
> 
>> Most definitely not. It is very deliberate that asdl_c.py is only
>> invoked when the ASDL sources change. Otherwise, having Python installed
>> would be a build requirement for Python, which it must be not.
> 
> OK, thanks for the background.  To be clear, though, the build dependency
> is already there.  You just have to touch the ASDL sources to run
> into it (Lib/opcode.py as well).  This is even documented in the
> Makefile*:

Just to be more clear: normally, generated files shouldn't be checked
into the source repository. However, exceptions are typically made for
generated files that may be difficult to regenerate on some target
systems. For Python, this includes configure (depends on autoconf being
run), and various files generated from Python scripts (also including
the Unicode database, for example).

So when we check in generated files, the build dependency becomes unused
unless the source file gets modified - which, as you point out, happens
rarely, and never happens for somebody who just wants to build Python.

> * If not relying on an external Python is a hard requirement (and I do
> see why that may be useful), then the build system could be changed to only allow changes to
> problematic sources (ASDL, opcode.py) after Python has been built once.  Then the built
> Python could be used.

See above. It's fine to require core contributors to have Python
installed (and also autoconf). We just need to make sure that
Python is not required on the target system (as people may try
to install Python initially on that system).