Startup script to use ipython (if available in environment) when python is ran without arguments

pythonrc.py

import os
import sys
import site

if len(sys.argv) == 1:
    del os.environ['PYTHONSTARTUP']
    sys.path.append(site.USER_SITE)

    try:
        if 'IPython' in sys.modules:
            raise ImportError('IPython is already imported')

        import IPython

        env = os.environ.copy()
        env['PYTHONPATH'] = site.USER_SITE
        print('Replacing with IPython...')
        os.execve(
            sys.executable, (os.path.basename(sys.executable), '-m', 'IPython'), env
        )
    except ImportError:
        try:
            import readline
            import rlcompleter

            readline.parse_and_bind('tab: complete')
        except ImportError:
            pass