Grid template tag for django

grid.py

from django import template
import re

register = template.Library()


def isNumber(x):
    return (type(x) is int) or (type(x) is float)


def grid_header_tag(parser, token):
    columnNames = token.split_contents()
    columnNames = map(lambda x : x[1:-1], columnNames[1:])
    return GridHeaderNode(columnNames)


class GridHeaderNode(template.Node):
    def __init__(self, columnNames):
        self.columnNames = columnNames

    def render(self, context):
        ret = "<tr>"
        for name in self.columnNames:
            ret += "<th class='text-center'>" + name + "</th>"
        ret += "</tr>"

        return ret


def grid_data_tag(parser, token):
    contents = token.split_contents()
    dataVarName = contents[1]
    columnVars = contents[2:]
    return GridDataNode(dataVarName, columnVars)


class GridDataNode(template.Node):
    def __init__(self, dataVarName, columnVars):
        self.dataVarName = template.Variable(dataVarName)
        self.columnVars = columnVars

    def render(self, context):
        data = self.dataVarName.resolve(context)
        ret = ""
        for line in data:
            ret += "<tr>"
            for varName in self.columnVars:
                try:
                    varName, align = varName.split("|")
                except:
                    align = None

                val = getattr(line, varName)
                attrs = ""
                if callable(val):
                    val = val()
                if isNumber(val):
                    attrs = "class='text-right'"

                if align == "c":
                    attrs = "class='text-center'"
                elif align == "l":
                    attrs = "class='text-left'"
                elif align == "r":
                    attrs = "class='text-right'"

                ret += "<td {} >{}</td>\n".format(attrs, val)
            ret += "</tr>"

        return ret


def grid_tag(parser, token):
    nodeList = parser.parse(("endgrid", ))
    parser.delete_first_token()
    return GridNode(nodeList)


class GridNode(template.Node):
    def __init__(self, nodeList):
        self.nodeList = nodeList

    def render(self, context):
        ret = "<table class='table table-bordered'>"
        for node in self.nodeList:
            if type(node) is GridHeaderNode:
                ret += "<thead>\n"
                ret += node.render(context)
                ret += "</thead>\n"
            elif type(node) is GridDataNode:
                ret += "<tbody>\n"
                ret += node.render(context)
                ret += "</tbody>\n"
        ret += "</table>"

        return ret


register.tag('grid', grid_tag)
register.tag('grid_header', grid_header_tag)
register.tag('grid_data', grid_data_tag)