webstats.py 4.0: Internal Maintenance Specification

This function finds the effective host list, given a primary host and a list of secondary hosts. Here's the interface:

# - - -   f i n d H o s t L i s t   - - -

def findHostList ( priHost, secHostList ):
    """Derive the effective host list.

      [ (priHost is the primary host as a string) and
        (secHostList is a list of secondary host names, each
        possibly with a trailing comma) ->
          return the effective host list as a list of strings ]
    """

There is a lengthy discussion of the derivation of the effective host list in the specification. The present function was not in the original design; it was broken out of the scanAccessGroup() function because there was just too much logic in that function's third prime.

The first case we eliminate is the case where secHostList contains either just "-" or an empty string. In that case, the effective host list contains only the primary host.

    #-- 1 --
    if  len(secHostList) == 0:
        return [ priHost ]
    else:
        firstSec  =  secHostList[0]

Next we eliminate the cases where the first secondary host is "-" or an empty string. In those cases, we again return a list containing just the primary host.

    #-- 2 --
    if  ( ( len ( firstSec ) == 0 ) or
          ( firstSec == "-" ) ):
       return [ priHost ]

At this point we have at least one secondary host. The result is this list, with any trailing commas removed from the elements.

    #-- 3 --
    hostList  =  []

    #-- 4 --
    # [ hostList  +:=  a list of the elements of secHostList with any
    #                  trailing commas removed ]
    for secHost in secHostList:
        if secHost.endswith(","):
            hostList.append ( secHost[:-1] )
        else:
            hostList.append ( secHost )

    #-- 5 --
    return hostList

What if one of the elements in secHostList is the empty string? The logic above that strips trailing commas is carefully constructed to work with empty strings. The Python expressions "".endswith(",") returns False, and the expression ""[:-1] returns the empty string.