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*  mailgroup.py  *
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  SUMMARY

  Program to produce a string that can be pasted into a mail client. The
  string is a list of email addresses that is constructed from 2 linked csv
  files: a database of email addresses, and a database of group names.

  USAGE

  mailgroup EMAIL_LIST GROUP_LIST [GROUPS]

  EMAIL_LIST is the path to a csv file containing the database of email
          addresses. The file must contain the colums (with a header row):
                  'Last name', 'First name', 'Email', 'Groups'
          Additional columns may be present (e.g. Position, Notes) but will
          not be used.

  GROUP_LIST is the path to a csv file containing the database of email
          groups. The file must contain the columns (with a header row):
              'Group', 'Key'

  [GROUPS]   is a logical expression built using the logical operators & | ~
          and parentheses (), as well as group names that exist in
          the GROUP_LIST file.

  If no arguments or the wrong number of arguments are passed then this
  message is returned.

  When EMAIL_LIST and GROUP_LIST are defined a string is returned to stdout
  that summarizes the number of names and groups in the database.

  When [GROUPS] is defined the output returned to stdout is a list of email
  addresses of members belonging to the groups listed in [GROUPS].

  Example command and output:
      $  mailgroup members.csv groups.csv (project1&project2)|management
      $  John Doe <j.doe@theinter.net>, Jane Q. Doe <jane.doe@theother.net>,
      $  James Manager <jims.your@boss.com>

  Note that commas are removed from member names stored in EMAIL_LIST, because
  these are interpreted as field separators by most email clients and
  interfaces.

  If you want to always use mailgroup with the same database, you can use an
  alias, then for a summary you just need enter mailgroup, or for a mailing
  list you only need provide the group expression.
  
  E.g. in ~/.bashrc:
    alias mailgroup='/usr/bin/mailgroup.py path2MyIndex.csv path2MyGroups.csv'

  Author: Elliot Sefton-Nash (e.sefton-nash@uclmail.net)