%

[Fredrik Lundh]

Phil Hunt <philh at vision25.demon.co.uk> wrote:
> Consider the % operator, eg:
> 
>     'All %(a)s eat %(b)s' % {'a':'cows', 'b':'grass'}
> 
> If the dictionary doesn't have all the relevant keys, an error
> occurs. Is it possible for me to change the behaviour of this so that
> if a key doesn't occur a default value of '' is assumed? 

class D:
    def __init__(self, dict=None, **extra):
        self.dict = dict or {}
        self.dict.update(extra)
    def __getitem__(self, key):
        try:
            return self.dict[key]
        except KeyError:
            return ""

print 'All %(a)s eat %(b)s' % {'a': 'cows', 'b': 'grass'}
print 'All %(a)s eat %(b)s' % D({'c': 'swines', 'b': 'pearls'})
print 'All %(a)s eat %(b)s' % D(a='pythoneers', b='spam')

</F>