Question

My mind is probably feeling Friday afternoon and I cannot see a way to pytonize the code below:

filepath = None
if 'HALLO' in os.environ:
    filepath = os.environ['HALLO']
elif os.path.isfile( os.path.join(os.environ['HOME'], 'host.hallo') ):
    filepath = os.path.join(os.environ['HOME'], 'host.hallo')
elif os.path.isfile('/etc/app/host.hallo'):
    filepath = '/etc/app/host.hallo'
if filepath:
    print 'HALLO found in "%s"' % filepath
    ## do something
else:
    print 'HALLO not found!'
    ## do something else

Any idea on how to do it? Thanks!

ps: the code above is just an example, it can have a syntax error since I have written it directly here.

Answer 1

home_hallo = os.path.join(os.environ['HOME'], 'host.hallo')
filepath = ( ('HALLO' in os.environ and os.environ['HALLO']) or
             (os.path.isfile(home_hallo) and home_hallo) or
             (os.path.isfile('/etc/app/host.hallo') and '/etc/app/host.hallo') )
if filepath:
    print 'HALLO found in "%s"' % filepath
    ## do something
else:
    print 'HALLO not found!'
    ## do something else

See the documentation on Boolean operations if it isn’t clear why this works, here is the summary:

The expression x and y first evaluates x; if x is false, its value is returned; otherwise, y is evaluated and the resulting value is returned.

The expression x or y first evaluates x; if x is true, its value is returned; otherwise, y is evaluated and the resulting value is returned.