code: def _make_cron_re():
      
      range_ = r"{val}(?:-{val}(?:/\d+)?)?"
      template = r"(?P<{name}>" + "(?:\*(?:/\d+)?|{r}(?:,{r})*)".format(r=range_) + ")\s+"
      return (
          r'^\s*' +
          template.format(name='minute', val=r'(?:\d|[012345]\d)') +
          template.format(name='hour', val=r'(?:\d|[01]\d|2[0123])') +
          template.format(name='day_of_month', val=r'(?:0?[1-9]|[12]\d|3[01])') +
          template.format(name='month', val=r'(?:0?[1-9]|1[012]|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)') +
          template.format(name='day_of_week', val=r'(?:[0-7]|mon|tue|wed|thur|fri|sat|sun)') +
          r'(?P<command>\S.*)$'
      )
docs: Make the regular expression that matches a crontab 'cron' line.
  
      Each field has a set of allowed values, and can then be in a range, and be
      listed with dashes.  A range can be stepped with the '/' modifier, and
      ranges can be in a list.  A field can also be '*', or '*' divided in steps.
  
      The best way to do this is to have a template for a single field that
      encapsulates the syntax of that field, regardless of what that field
      matches.  We then fill in the actual template's value with the pattern
      that matches that field.  Each field is named, so we can pull them out as
      a dictionary later.