./configure does not support Python 3

[Mateusz Łoskot]

This problem occured to me in Linux environment where /usr/bin/python points to Python 3.x but not Python 2.x:

mloskot gdal $ python -V
Python 3.2.3
mloskot gdal $ python2 -V
Python 2.7.3

Here are the symptoms:

mloskot gdal $ ./configure --with-python
...
checking for location of Python Makefiles...   File "<string>", line 3
    print sys.prefix
            ^
SyntaxError: invalid syntax
  File "<string>", line 3
    print sys.prefix
            ^
SyntaxError: invalid syntax
  File "<string>", line 3
    print sys.version[:3]
            ^
SyntaxError: invalid syntax
found
checking where to install Python modules... /lib/python/site-packages
enabled
checking for python setuptools...   File "<string>", line 3
    print 1
          ^
SyntaxError: invalid syntax
not found
...

It also means that AM_PATH_PYTHON macro called by ./configure does not check version of Python found.

Likely, improving ./configure to support Python 3.x will involve adding new option --with-python3 to avoid ambiguities.

[Mateusz Łoskot]

Quick fix makes ./configure too look for python2 first, so python is not looked for in case /usr/bin/python is Python 3.x executable

[Even Rouault]

I've followed another route by removing a lot of old stuff that was likely needed by the old-gen python bindings. Now --with-python should work with either python 2 or 3, and it can also now accept as argument the path to / name of the wished python binary. For example --with-python=python2.7 or --with-python=python3.2

trunk r24948 : --with-python: make it work with python3, and also accept path to python binary as argument of --with-python (#4725)

[Even Rouault]

r25008 "Unix configure: avoid ./configure to fail with default arguments if Python isn't available (trunk only, fix r24948, #4725)"