IntroduceVariableCommand.py

import sublime
import sublime_plugin
import re

class IntroduceVariableCommand(sublime_plugin.TextCommand):

    var_name = "NewVar"

    def run(self, edit):

        sels = self.view.sel()

        for sel in sels:  
            if not sel.empty():
                self.introduce_variable(edit, sel)
                
    def introduce_variable(self, edit, sel):
        sel_text    = self.view.substr(sel)
        top_line    = self.view.lines(sel)[0]
        top_line_text = self.view.substr(top_line)
        indentation = ""

        match = re.search(r"\W*", top_line_text, re.UNICODE)

        if match:
            indentation = match.group(0)

        var_declaration = indentation + self.var_name + " = " + sel_text + ",\n"

        self.view.replace(edit, sel, self.var_name)

        self.view.insert(edit, top_line.a, var_declaration)