Please read Formatting code and log snippets in posts and reformat your code appropriately.
Check your quotes, they are not consistents.
It is not clear if srcQuery is an array with an object or if it is still a string. Share the code you use tk read the string from mongo and that parse it into an array.
Is it
you want to inject or var_id and todaysdate?
Where did you find that you could use ${var_id} to substitute variables in a string? Any reference to python API that mentioned that? The dollar syntax is more a shell thing rather than python. May be what you want is more like