How we develop better apps

The biggest mistake new Frappe developers make is they don't log.

Just type "error log" in the awesome search bar in ERPNext. You can see the generated error logs. This is how developers get info about the errors in production.

For instance this is how we log SQL Server queries:

if docJLSettings.ld_log_sql_server_queries:

    frappe.log_error(_("Query Result for {0} is {1}").format(strLogDescription, lstResult), _("Jet Lazer"))

So you can review and filter your logs.

And you can examine the log:

You can generate descriptive log messages:

frappe.log_error(frappe.get_traceback(), _("Calculate rate failed in sales order."))

You can enrich them:

frappe.log_error(_("Calculate rate failed in {0}. Customer: {1}, Total:{2}, Error:{3}.").format(doc.doctype, doc.customer, doc.grand_total, frappe.get_traceback()), _("Calculate Rate in My App"))

You can also use:

frappe.errprint("Error occured.")

which prints info to the console on development environment and logs the error. So you can trace it when you need it.