def foobar(arg):
   if arg == 'foo':
       return None
   else:
       return 'bar'

foobar('sdfsdgf').upper()
foobar('foo').upper()

tmp = foobar('foo')
if tmp is not None:
    tmp.upper()
# or
try:
    foobar('foo').upper()
except ArgumentError:
    pass
# or
caller = lambda x: x.upper() if type(x) is str else None
caller(foobar('foo'))

(foobar('foo') or '').upper()

def forward_none(func):
    def wrapper(arg):
        return None if arg is None else func(arg)
    return wrapper

forward_none(str.upper)(foobar('foo'))

@forward_none
def do_interesting_things(value):
    # code that assumes value is not None...

do_interesting_things(None) # ignores the original code and evaluates to None
do_interesting_things("something") # as before decoration

from pymaybe import maybe
maybe(foobar('foo')).upper()