def indentedBlock(blockStatementExpr, indentStack, indent=True):
    """Helper method for defining space-delimited indentation blocks, such as
       those used to define block statements in Python source code.

       Parameters:
        - blockStatementExpr - expression defining syntax of statement that
            is repeated within the indented block
        - indentStack - list created by caller to manage indentation stack
            (multiple statementWithIndentedBlock expressions within a single grammar
            should share a common indentStack)
        - indent - boolean indicating whether block must be indented beyond the
            the current level; set to False for block of left-most statements
            (default=True)

       A valid block must contain at least one C{blockStatement}.
    """
    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
dataset/ETHPy150Open Exa-Networks/exabgp/lib/exabgp/dep/pyparsing.py/indentedBlock/original