def indentedBlock(blockStatementExpr, indentStack, indent=True):
    def checkPeerIndent(s,l,t):
        if l >= len(s): return
        curCol = col(l,s)
        if curCol != indentStack[-1]:
            if curCol > indentStack[-1]:
                raise ParseFatalException(s,l,"illegal nesting")
            raise ParseException(s,l,"not a peer entry")

    def checkSubIndent(s,l,t):
        curCol = col(l,s)
        if curCol > indentStack[-1]:
            indentStack.append( curCol )
        else:
            raise ParseException(s,l,"not a subentry")

    def checkUnindent(s,l,t):
        if l >= len(s): return
        curCol = col(l,s)
        if not(indentStack and curCol < indentStack[-1] and curCol <= indentStack[-2]):
            raise ParseException(s,l,"not an unindent")
        indentStack.pop()

    NL = OneOrMore(LineEnd().setWhitespaceChars("\t ").suppress())
    INDENT = Empty() + Empty().setParseAction(checkSubIndent)
    PEER   = Empty().setParseAction(checkPeerIndent)
    UNDENT = Empty().setParseAction(checkUnindent)
    if indent:
        smExpr = Group( Optional(NL) +
            FollowedBy(blockStatementExpr) +
            INDENT + (OneOrMore( PEER + Group(blockStatementExpr) + Optional(NL) )) + UNDENT)
    else:
        smExpr = Group( Optional(NL) +
            (OneOrMore( PEER + Group(blockStatementExpr) + Optional(NL) )) )
    blockStatementExpr.ignore(_bslash + LineEnd())
    return smExpr
Helper method for defining space-delimited indentation blocks, such as
dataset/ETHPy150Open ipython/ipython-py3k/IPython/external/pyparsing/_pyparsing.py/indentedBlock