Skip messages via Jinja template about mailmerge HOT 7 OPEN

One way to do it is to make a copy of the CSV file and delete some of the rows with a text editor. Another way to do it is to filter the CSV file using command line tools like grep or csvkit.

Finally, here's an example of how to use the command line options to skip a message, e.g., message 11.

$ mailmerge --limit 10
$ mailmerge --resume 12

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Here's a brain dump of some different ways this could work. Feedback welcome.

1. Include row numbers, similar to the cut -f option. From man cut:

   $ mailmerge --include-rows 1-10,13-20
   $ man cut
   ...
   Use one, and only one of -b, -c or -f.  Each LIST is  made  up  of  one
   range,  or  many ranges separated by commas.  Selected input is written
   in the same order that it is read, and is written exactly  once.   Each
   range is one of:
   
   N      N'th byte, character or field, counted from 1
   
   N-     from N'th byte, character or field, to end of line
   
   N-M    from N'th to M'th (included) byte, character or field
   
   -M     from first to M'th (included) byte, character or field

2. Exclude row numbers, e.g.:

   $ mailmerge --exclude-rows 11-12

3. Pattern match against a column, similar to csvgrep.

   $ mailmerge --column email --match umich.edu
   $ mailmerge --column email --match umich.edu --invert-match

4. Skip message if entire rendered template is blank. This is similar to the suggestion of @kapgit above. I'd perhaps couple it with a command line flag. Perhaps check for blank messages and produce a helpful error message, suggesting this flag.

   $ mailmerge --skip-blank

   And the corresponding mailmerge_template.txt:

   {% if condition_based_on_current_record -%}
   TO: {{email}}
   FROM: [email protected]
   
   Hello world
   {% endif -%}
   

5. Skip message if TO field is blank. EDIT: possible bug could be if there's a CC or BCC field. TO, CC and BCC all end up in the senders list.

   $ mailmerge --skip-blank-to

   And the corresponding mailmerge_template.txt:

   {% if condition_based_on_current_record -%}
   TO: {{email}}
   {% endif -%}
   
   FROM: [email protected]
   
   Hello world
   

I'm leaning towards option 4, similar to @kapgit 's suggestion above.

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Maybe there is a better method, but at the moment, I'm applying a quick and dirty solution that seems to work for me:

In template_message.py (commented the 3 assertions):

    def render(self, context):
        """Return rendered message object."""
        try:
            raw_message = self.template.render(context)
        except jinja2.exceptions.TemplateError as err:
            raise MailmergeError(
                "{}: {}".format(self.template_path, err)
            )
        self._message = email.message_from_string(raw_message)
        self._transform_encoding(raw_message)
        self._transform_recipients()
        self._transform_markdown()
        self._transform_attachments()
        self._message.__setitem__('Date', email.utils.formatdate())
        #assert self._sender # COMMENTED
        #assert self._recipients # COMMENTED
        #assert self._message # COMMENTED
        return self._sender, self._recipients, self._message

In __main__.py (enclosed the 'sendmail' in an 'if' statement):

def main(sample, dry_run, limit, no_limit, resume,
         template_path, database_path, config_path,
         output_format):
...
   try:
        template_message = TemplateMessage(template_path)
        csv_database = read_csv_database(database_path)
        sendmail_client = SendmailClient(config_path, dry_run)
        for _, row in enumerate_range(csv_database, start, stop):
            sender, recipients, message = template_message.render(row)
            if sender and recipients and message: # ADD THIS LINE + INDENT FOLLOWING
                sendmail_client.sendmail(sender, recipients, message)
                print_bright_white_on_cyan(
                    ">>> message {message_num}"
                    .format(message_num=message_num),
                    output_format,
                )
                print_message(message, output_format)
                print_bright_white_on_cyan(
                    ">>> message {message_num} sent"
                    .format(message_num=message_num),
                    output_format,
                )
                message_num += 1

    except MailmergeError as error:
...

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It'd be great to see a flag or similar for this if we can do it in a UI friendly way. I have a routine email that I send that needs to come from one of two email addresses. Today I have to bifurcate my data set and reset the conf for each run. Not having to bifurcate the data set would be a small win.

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@awdeorio I like what you have. FWIW, I'd like to express my preference for number 5 because it is smaller and keeps the if small to prevent weird nesting typos later.

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+1 for (5). Empty to currently results in a assertion error, so its anyway not a supported usecase.

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I can get behind (5). Any volunteers? :)

I think this would involve:

• Code to add command line flag
• Code to add "skip" functionality
• Unit test: basic, with both skipped and not-skipped messages. Include CC, BCC.
• Unit test: jinja logic results in blank "TO". User forgets the command line flag. Probably should error with a helpful message in this case.
• Documentation. Maybe an "advanced usage" subsection?

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