I want to apply a function to all values in dict and store that in a separate dict. I am just trying to see how I can play with python and want to see how I can rewrite something like this
for i in d:
d2[i] = f(d[i])
to something like
d2[i] = f(d[i]) for i in d
The first way of writing it is of course fine, but I am trying to figure how python syntax can be changed
If you're using Python 2.7 or 3.x:
d2 = {k: f(v) for k, v in d1.items()}
Which is equivalent to:
d2 = {}
for k, v in d1.items():
d2[k] = f(v)
Otherwise:
d2 = dict((k, f(v)) for k, v in d1.items())
d2 = dict((k, f(v)) for k,v in d.items())
Dictionaries can be nested in Python and in this case the solution d2 = {k: f(v) for k, v in d1.items()}
will not work.
For nested dictionaries one needs some function to transverse the whole data structure. For instance if values are allowed to be themselves dictionaries, one can define a function like:
def myfun(d):
for k, v in d.iteritems():
if isinstance(v, dict):
d[k] = myfun(v)
else:
d[k] = f(v)
return d
And then
d2 = myfun(d)
If you don't mind using an extension. You can also use toolz very own valmap
:
from toolz.dicttoolz import valmap
d2 = valmap(f, d)
If not for the clean presentation of the method, you also have the option of supplying a default return class as well so for people that need something other than a dict
.
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