String formatting with nested dictionaries
Fredrik Lundh
fredrik at pythonware.com
Thu Aug 24 15:02:51 EDT 2006
linnorm at gmail.com wrote:
> I've got a bit of code which has a dictionary nested within another
> dictionary. I'm trying to print out specific values from the inner
> dict in a formatted string and I'm running into a roadblock. I can't
> figure out how to get a value from the inner dict into the string. To
> make this even more complicated this is being compiled into a large
> string including other parts of the outer dict.
>
> mydict = {'inner_dict':{'Value1':1, 'Value2':2}, 'foo':'bar',
> 'Hammer':'nails'}
>
> print "foo is set to %(foo)s - Value One is: %(inner_dict['Value1'])s
> and Value Two is: %(inner_dict['Value2'])s -- Hammers are used to pound
> in %(Hammer)s" % mydict
>
> The above fails looking for a key named 'inner_dict['Value1']' which
> doesn't exist.
the % operator treats the keys as plain keys, not expressions. if you
trust the template provider, you can use a custom wrapper to evaluate
the key expressions:
mydict = {'inner_dict':{'Value1':1, 'Value2':2}, 'foo':'bar',
'Hammer':'nails'}
class wrapper:
def __init__(self, dict):
self.dict = dict
def __getitem__(self, key):
try:
return self.dict[key]
except KeyError:
return eval(key, self.dict)
print "foo is set to %(foo)s - Value One is: %(inner_dict['Value1'])s
and Value Two is: %(inner_dict['Value2'])s -- Hammers are used to pound
in %(Hammer)s" % wrapper(mydict)
foo is set to bar - Value One is: 1 and Value Two is: 2 -- Hammers are
used to pound in nails
</F>
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