What is wrong with this piece of code?
dic = { 'fruit': 'apple', 'place':'table' }
test = "I have one {fruit} on the {place}.".format(dic)
print(test)
>>> KeyError: 'fruit'
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1Possible duplicate of stackoverflow.com/questions/5952344/…Frank– Frank2019-05-16 20:17:59 +00:00Commented May 16, 2019 at 20:17
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3 Answers
Should be
test = "I have one {fruit} on the {place}.".format(**dic)
Note the **. format() does not accept a single dictionary, but rather keyword arguments.
5 Comments
bogdan
Thanks, it works. Can you update the answer to explain why I have to add
** before the dictionary?
Mark Ransom
@bogdan, the
** indicates that the dictionary should be expanded to a list of keyword parameters. The format method doesn't take a dictionary as a parameter, but it does take keyword parameters.
Sven Marnach
@bogdan: Added two links to my answer. The reason basically is "because the documentation says so".
Michael Smith
@bogdan That just tells Python that you are providing a dictionary to the function so that it can provide the values in the dictionary, rather than the dictionary itself. You can do the same when calling any function. If function 'f' takes the args 'a','b', and 'c', you could use
dic = {'a':1,'b':2,'c':3} and call f(**dic).
Jochen Ritzel
The reason is that
"I have one {0[fruit]} on the {0[place]}.".format(dic) works too - dic is the 0th positional argument here and you can access it's keys in the template.There is ''.format_map() function since Python 3.2:
test = "I have one {fruit} on the {place}.".format_map(dic)
The advantage is that it accepts any mapping e.g., a class with __getitem__ method that generates values dynamically or collections.defaultdict that allows you to use non-existent keys.
It can be emulated on older versions:
from string import Formatter
test = Formatter().vformat("I have one {fruit} on the {place}.", (), dic)
Comments
You can use the following code too:
dic = { 'fruit': 'apple', 'place':'table' }
print "I have one %(fruit)s on the %(place)s." % dic
If you want to know more about format method use: http://docs.python.org/library/string.html#formatspec
6 Comments
Mark Ransom
The
% operator shouldn't be used in new code according to the Python documentation.
Artsiom Rudzenka
Could you please give me a reference so i will be able to read more on this?
Artsiom Rudzenka
Thank you very much), will try to avoid using it from now
Sven Marnach
@Mark:
% was meant to be deprecated in Python 3.1, but they never did. It won't go away soon (or probably not at all), so it's ok to still use it.Mark Ransom
@Sven, good to know, thanks. Still I'd go with
format first because it's recommended, second because it seems cleaner. |