Retrieving Key and Values from Dictionary

Question

I used a Dictionary as shown below:

streetno={
    "1":"Sachin Tendulkar",
    "2":"Sehawag",
    "3":"Dravid",
    "4":"Dhoni",
    "5":"Kohli"
}

After this I'm asking user for i/p. Then, depending upon the user input I want to retrieve either key or value from the dictionary. How can I implement this?? Which method I can use to implement this??

Could you please qualify your requirements? In what case do you want the value, and in what case do you want the key? — Platinum Azure, Jan 03 '12 at 18:38
If user enters integer then i want to retrieve corresponding string value. If user enters the string value I want to corresponding key.. — Kiran Bhat, Jan 03 '12 at 18:42

Andrew Clark · Accepted Answer · 2012-01-03T18:58:14.287

I may be misunderstanding this, but it looks like you may be asking a user to give you either a key or a value. If they give you a key you want to return the value and if they give you a value you want to return the key.

If that is what you are looking for, the easiest way to do this is to add entries to the dictionary with the values and keys swapped, for example:

streetno={"1":"Sachin Tendulkar","2":"Sehawag","3":"Dravid","4":"Dhoni","5":"Kohli"}
streetno.update([(v, k) for k, v in streetno.items()])

This results in the following dictionary:

>>> pprint(streetno)
{'1': 'Sachin Tendulkar',
 '2': 'Sehawag',
 '3': 'Dravid',
 '4': 'Dhoni',
 '5': 'Kohli',
 'Dhoni': '4',
 'Dravid': '3',
 'Kohli': '5',
 'Sachin Tendulkar': '1',
 'Sehawag': '2'}

With this you can get the input and look up the value in the dictionary without any additional checking:

key = raw_input("Enter name or number (i/p):")
result = streetno.get(key)

If you are using Python 3.x, replace raw_input() with input().

NPE · Answer 2 · 2012-01-03T18:57:15.613

0

You could create an auxiliary dictionary with the reverse mappings:

In [4]: dict((v,k) for k,v in streetno.items())
Out[4]: 
{'Dhoni': '4',
 'Dravid': '3',
 'Kohli': '5',
 'Sachin Tendulkar': '1',
 'Sehawag': '2'}

Once you know which way you need to map, you either use the original or the auxiliary dictionary for the lookup.

edited Jan 03 '12 at 18:57

answered Jan 03 '12 at 18:47

NPE

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Note that `iteritems()` is deprecated since Python 2.7 and will be gone in Python 3.x – moooeeeep Jan 03 '12 at 18:54

score 0 · Answer 3 · edited May 23 '17 at 12:20

If the user inputs an "integer", you can explicitly index into the dictionary (i.e. streetno[value]). Your keys appear to be strings, so you can get away with not having to cast them as integers or do anything to get around the issue that it could be a string or integer. If your keys were integers, then you would have to do a bit of casting and finagling - which I leave as an exercise to you.

As for the other way 'round, if you want to create a reverse mapping of the dictionary (which I think you do), then you'd be best to take a look at this SO question and answer. You would have to create a separate dictionary for it, and use that method to map the key values backwards.

score 0 · Answer 4 · answered Jan 03 '12 at 18:51

A small code sample to get you started...

streetno =
    {
     "1":"Sachin Tendulkar",
     "2":"Sehawag",
     "3":"Dravid",
     "4":"Dhoni",
     "5":"Kohli"
     }

input=raw_input()
try:
    print streetno[input]
except KeyError:
    print [k for k, v in streetno.items() if v == input][0]

score -1 · Answer 5 · answered Jan 03 '12 at 18:45

-1

Check the "Dictionaries" section on this site for documentation: http://docs.python.org/tutorial/datastructures.html

streetno.keys() delivers the keys and you can iterate over the keys to get the values:

pseudo-code:


        foreach key in streetno.keys()
            print "key: ", key, ", value: ", streetno[ key ]

answered Jan 03 '12 at 18:45

boto

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This doesn't answer the question...it just prints every key-value pair. – Makoto Jan 03 '12 at 19:01
The purpose of the post was reading the documentation about dictionaries. I assume that the reader understands how the dictionaries work in Pyhton after reading the documentation! – boto Jan 03 '12 at 19:10

Retrieving Key and Values from Dictionary

5 Answers5