def METHOD_NAME(env):
    '''Find Python executable to use.'''
    if 'PYTHON' in env:
        return env['PYTHON']
    p = env.WhereIs('python3')
    if p:
        return env['ESCAPE'](p)
    p = env.WhereIs('py.exe')
    if p:
        return env['ESCAPE'](p) + " -3"
    return env['ESCAPE'](sys.executable)