#!/usr/bin/env python
import pyparsing as pp
from pprint import pprint

indentStack = [1]
stmt = pp.Forward()
suite = pp.Group(pp.indentedBlock(stmt, indentStack)).setName("suite") #.setDebug()
command = (pp.Keyword("open") | pp.Keyword("close")).setName("command") #.setDebug()
funcDecl = (pp.Keyword("def") + pp.Word(pp.printables)).setName("function_declaration") #.setDebug()
funcDef = (funcDecl + suite).setName("function_definition") #.setDebug()
stmt << ( funcDef | command)
module_body = pp.OneOrMore(stmt)

code="""\
def process
    open
    close"""

print("example: indentStack: ", indentStack, hex(id(indentStack)))
print("example: funcDef    : ", funcDef)
f1 = funcDef.parseString(code)  ### works fine

# indentStack = [1]
indentStack.pop()

print("example: indentStack: ", indentStack, hex(id(indentStack)))
print("example: funcDef    : ", funcDef)
f2 = funcDef.parseString(code)



Execution
---------
(py3.6.1) [backend@gc-backend-2 backend]$ python pp2.py
example: indentStack:  [1] 0x7fd7e281c388        <----- the first instance of indentStack
example: funcDef    :  function_definition
checkSubIndent: curCol     :  5
checkSubIndent: indentStack:  0x7fd7e281c388     <----- the first instance of indentStack
checkSubIndent: indentStack:  [1]
checkSubIndent: indentStack:  [1, 5]  (append)
example: indentStack:  [1] 0x7fd7e281c388        <----- the first instance of indentStack
example: funcDef    :  function_definition
checkSubIndent: curCol     :  5
checkSubIndent: indentStack:  0x7fd7e281c388     <----- the first instance of indentStack
checkSubIndent: indentStack:  [1]
checkSubIndent: indentStack:  [1, 5]  (append)