python-shell-virtualenv-root

python-shell-virtualenv-root is a variable defined in `python.el'.
Its value is

nil

• This variable is safe as a file local variable if its value
  satisfies the predicate `stringp'.

Documentation:
Path to virtualenv root.
This variable, when set to a string, makes the values stored in
`python-shell-process-environment' and `python-shell-exec-path'
to be modified properly so shells are started with the specified
virtualenv.

You can customize this variable.