Proof of concept to see the possibility to inherit venvs in an easy way

birtualenb.py

import os
import sys
import argparse
import subprocess
from venv import EnvBuilder

# Custom options
parser = argparse.ArgumentParser(description='inherit venvs')
parser.add_argument(
    '--other-venv-paths', 
    nargs='+',
    help="Paths to other venvs"
)
# default venv options
parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
                    help='A directory to create the environment in.')
parser.add_argument('--system-site-packages', default=False,
                    action='store_true', dest='system_site',
                    help='Give the virtual environment access to the '
                         'system site-packages dir.')
if os.name == 'nt':
    use_symlinks = False
else:
    use_symlinks = True
group = parser.add_mutually_exclusive_group()
group.add_argument('--symlinks', default=use_symlinks,
                   action='store_true', dest='symlinks',
                   help='Try to use symlinks rather than copies, '
                        'when symlinks are not the default for '
                        'the platform.')
group.add_argument('--copies', default=not use_symlinks,
                   action='store_false', dest='symlinks',
                   help='Try to use copies rather than symlinks, '
                        'even when symlinks are the default for '
                        'the platform.')
parser.add_argument('--clear', default=False, action='store_true',
                    dest='clear', help='Delete the contents of the '
                                       'environment directory if it '
                                       'already exists, before '
                                       'environment creation.')
parser.add_argument('--upgrade', default=False, action='store_true',
                    dest='upgrade', help='Upgrade the environment '
                                       'directory to use this version '
                                       'of Python, assuming Python '
                                       'has been upgraded in-place.')
parser.add_argument('--without-pip', dest='with_pip',
                    default=True, action='store_false',
                    help='Skips installing or upgrading pip in the '
                         'virtual environment (pip is bootstrapped '
                         'by default)')

args = parser.parse_args()

def parse_stdout(mystr):
    mystr = mystr.decode('utf')
    mystr = (mystr.replace('"','')
                  .replace("'",'')
                  .replace("[",'')
                  .replace("]",'')
                  .replace("\n",'')
            )
    mystr = mystr.split(',')
    return [v.rstrip().lstrip() for v in mystr if 'site-packages' in v]

def main():
    if args.upgrade and args.clear:
        raise ValueError('you cannot supply --upgrade and --clear together.')
    builder = EnvBuilder(system_site_packages=args.system_site,
                         clear=args.clear,
                         symlinks=args.symlinks,
                         upgrade=args.upgrade,
                         with_pip=args.with_pip)
    for d in args.dirs:
        builder.create(d)
            
if __name__ == '__main__':
    # Create the new venv
    rc = 1
    try:
        main()
        rc = 0
    except Exception as e:
        print('Error: %s' % e, file=sys.stderr)
    #sys.exit(rc)
    
    if args.other_venv_paths:
        other_paths = args.other_venv_paths
        sys_path = []
        for path in other_paths:
            python_path = os.path.join(path, 'bin', 'python')
            print(python_path)
            proc = subprocess.Popen(
                [python_path, "-c", "import sys; print(sys.path)"], 
                stdout=subprocess.PIPE
            )
            sys_path.append(parse_stdout(proc.communicate()[0]))
        pyvers = 'python{0}.{1}'.format(*sys.version_info[0:2])
        for d in args.dirs:
            path = os.path.join(d, 'lib', pyvers, 'site-packages')
            usercustomize = open(
                os.path.join(path, 'sitecustomize.py'),
                'w'
            )
            usercustomize.write(
"""print('Loading superior venvs')
import sys
    
""")
            for other_path in sys_path:
                print(other_path)
                usercustomize.write(
                    "sys.path.append('{}')\n".format(other_path[0])
                )
            usercustomize.close()