Mini Shell

# coding: utf-8
from __future__ import print_function
from __future__ import division
from __future__ import absolute_import
import glob
import os
import re
import errno
from subprocess import check_output, CalledProcessError, STDOUT

# Used both for config and some state like available_versions cache
# mainly because it's easier to put it in cagefs as a one dir
# We have symlink to that dir in /etc
# for ease of use the selector config and avoiding problem with cagefs

CONFIG_DIR = '/usr/share/l.v.e-manager/cl.python'

ALT_NAMES = 'alt-python'
# It's also used to construct base_dir:
ALT_PYTHON_PREFIX = '/opt/alt/python'


class PythonError(Exception):
    """Top level error class for admin's part of Python selector"""
    pass


class PythonConfigError(PythonError):
    """Generic error class for PythonConfig"""
    pass


def create_config_dirs():
    try:
        os.makedirs(CONFIG_DIR)
    except OSError as e:
        if e.errno != errno.EEXIST:  # ignore only "File exists" error
            raise


def is_major_version(ver):
    """Return True if specified MAJOR version is valid for processing"""
    if not isinstance(ver, str):
        return False
    if not re.match(r'^\d+\.\d+$', ver):
        return False
    return True


def scan_python_versions():
    """ Search CL python interpreters and return dict with info about them """
    res = {}
    for folder in glob.glob('{}*'.format(ALT_PYTHON_PREFIX)):
        # extract major version of python interpreter
        # get two last digits from the string such as `/opt/alt/python27`

        maj_ver = ''.join(filter(str.isdigit, folder.split('/')[-1]))
        maj_ver = f'{maj_ver[0]}.{maj_ver[1:]}'
        # extract full version of python interpreter
        # from the string such as `Python 2.7.14`
        python_bin = '{}/bin/python{}'.format(folder, maj_ver)
        if not os.path.isfile(python_bin):
            continue
        try:
            # Starting from 3.4, python command output --version information to stdout instead of stderr
            # https://docs.python.org/3/whatsnew/3.4.html#changes-in-python-command-behavior
            full_ver = check_output([python_bin, '-V'], text=True, stderr=STDOUT)
        except CalledProcessError:
            continue
        if full_ver != "":
            full_ver = full_ver.split()[1]
            res[maj_ver] = {
                'full_version': full_ver,
                'root_path': folder,
            }
    return res


__all__ = (
    'CONFIG_DIR',
    'ALT_NAMES',
    'ALT_PYTHON_PREFIX',
    'PythonError',
    'PythonConfigError',
    'create_config_dirs',
    'is_major_version',
    'scan_python_versions',
)