One of Those Things

Check out this question on Stack Overflow: "Python: replace a string by a float in txt file".

The question is confusing, but it appears to be a longish and confused description of simple formatting or template substitution.  It's hard to be sure, but it sounds like one of Those Things™ (TT).

Most of Those Things (TT) are standard problems with standard solutions.  Until you've seen a lot TT's, it seems like your problem is unique and special.  It's hard to see TT's for what they are.

In this case, the problem appears to be solved by Python's string.Template class with minor modifications.  The documentation for customizing string.Template isn't clear, so here's an example.


from string import Template
class MyTemplate( Template ):
    delimiter= '@'
    pattern= r"@(?P<escaped>@)|@(?P<named>[_a-z][_a-z0-9]*)@|@(?P<braced>[_a-z][_a-z0-9]*)@|@(?P<invalid>)"


That appears to be the standard solution to the standard problem.  Define a new delimiter ('@') and some slightly different delimiter parsing rules and away you go.

This can be used as follows to replace any '@x@' variables in any template file.  What's important is that very little actual code is needed, since it's one of Those Things that's already been solved.

with open( 'a.txt', 'r' ) as source:
    t = MyTemplate(source.read())
    result= t.substitute( x=15 )
    print result


Code Base Fragmentation -- Again

Check this out: "Stupid Template Languages".

Love this: "The biggest annoyance I have with smart template languages (Mako, Genshi, Jinja2, PHP, Perl, ColdFusion, etc) is that you have the capability to mix core business logic with your end views, hence violating the rules of Model-View-Controller architecture."

Yes, too much power in the template leads to code base fragmentation: critical information is not in the applications, but is pushed into the presentation. This also happens with stored procedures and triggers.

I love the questions on Stack Overflow (like this one) asking how to do something super-sophisticated in the Django Template language. And the answer is often "Don't. That's what view functions are for."