Python: Generating strings dynamically (based on some templates)

Question

I am trying to generate specific xml strings from my module, based on the type of string requested by some code using my module. Each of these xml strings contains some data that gets generated dynamically. For example, many of these xml strings have a cookie field that is generated using another function.

I started out with a python dictionary that initializes all the xml strings with the dynamic field (ie cookie) pre-populated (ie, not exactly dynamic). And then I call the dictionary to get the relevant xml strings.

The problem with this approach is that the cookies expire every hour and therefore the strings being returned by the module after an hour have those expired values. What I would ideally like to have is some form of a generator function (not sure if that's even possible in this case) that returns the correctly formed strings as and when they are requested based on the msg_type requested (as in the example below). Each of the xml strings saved in this dict is in a unique format, so I can't exactly have some sort of a common template xml generator.

As an example, the dict that I have defined looks similar to get_msg dictionary here:

    get_msg["msg_value_1"] = """<ABC cookie=""" + getCookie() + """ > 
                                     <XYZ """ + foo_name +""">
                                     </XYZ>
                              </ABC>"""

    get_msg["msg_value_2"] = """<ABC cookie=""" + getCookie() + """ > 
                                     <some text """ + bar_name + """>
                                     </XYZ>
                              </ABC>"""

What would be a good approach to be able to generate these xml strings on the fly with getCookie() getting invoked for every fresh msg request. Any input would be appreciated.

It might be easier to find an XML reader/writer to do all of this for you. Here's a quick tutorial that may help: codeghar.wordpress.com/2010/10/18/… — BenDundee
– BenDundee, Commented Jan 28, 2013 at 22:33

Borealid · Accepted Answer · 2013-01-29 14:09:51Z

In Python, functions are first-class objects. This means you can pass a function as an argument to another function.

def get_msg(function_to_call_to_get_injection_bit, tag_name_function,
            cookie_function):

    tagname = tag_name_function()
    injection = function_to_call_to_get_injection_bit()
    cookie = cookie_function()

    return '<ABC cookie="%s">' % (cookie) +
               '<%s %s></%s></ABC>' % (tagname, injection, tagname)

def get_injection():
    return foo_name

def get_tag_name_1():
    return "XYZ"

def get_tag_name_2():
    return "SomeText"

get_msg(get_injection, get_tag_name_1, getCookie)
get_msg(get_injection, get_tag_name_2, getCookie)

You just call get_msg every time you want a message, and pass it the function(s) that generate the portion of the message not related to the cookie.

From your question it's not entirely clear what the issue is. But this isn't really a "generator function": I don't think you want to return a function (which is possible), you want to return the XML string and just customize how it's built.

As BenDundee commented above, it'd probably also be better to use an XML library to build XML, instead of constructing the strings by hand. Python has several options built in, and more available outside (like the wonderful lxml library).

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