Cog is designed to be easy to run. It writes its results back into the original file while retaining the code it executed. This means cog can be run any number of times on the same file. Rather than have a source generator file, and a separate output file, typically cog is run with one file serving as both generator and output.

Because the marker lines accommodate any language syntax, the markers can hide the cog Python code from the source file. This means cog files can be checked into source control without worrying about keeping the source files separate from the output files, without modifying build procedures, and so on.

I experimented with using a templating engine for generating code, and found myself constantly struggling with white space in the generated output, and mentally converting from the Python code I could imagine, into its templating equivalent. The advantages of a templating system (that most of the code could be entered literally) were lost as the code generation tasks became more complex, and the generation process needed more logic.

Cog lets you use the full power of Python for text generation, without a templating system dumbing down your tools for you.