Python format throws KeyError

Question

The following code snippet:

template = \"\\                                                                                
function routes(app, model){\\            


        

Answer 1

Well, just another way of doing this without format could be:

In [1673]: className = 'myclass'                                                                                                                                                                            

In [1674]: template = 'function routes(app, model){app.get("/preNew"{'+className+'}, function(req, res){res.render({"'+className+'".ejs, {});});});'                                                        

In [1675]: template                                                                                                                                                                                         
Out[1675]: 'function routes(app, model){app.get("/preNew"{myclass}, function(req, res){res.render({"myclass".ejs, {});});});'

Answer 2

You have a number of unescaped braces in that code. Python considers all braces to be placeholders and is trying to substitute them all. However, you have only supplied one value.

I expect that you don't want all your braces to be placeholders, so you should double the ones that you don't want substituted. Such as:

template = """                                                                  
function routes(app, model){{
  app.get('/preNew{className}', function(req, res){{
    res.render('{className}'.ejs, {{}});                                           
  }};                                                      
}});""".format(className=className)

I also took the liberty of using triple quotes for the string literal so you don't need the backslashes at the end of each line.