I have a python code which converts JSON text file to a shapefile. I have to set coordinate system to this shapefile created. I do not want to access the .prj file from my computer as this code will be embedded in a web toolbox.
There is no way to set a shapefile's coordinate system without the .prj file. Without knowing your platform it's hard to provide advice. You mention a 'web toolbox' and python. If you know the input coordinate system of your JSON text file(which I'm betting is WGS84 lat/lon). You could build a generic .prj file on the fly to kick back to the user to accompany the generated shapefile.