Dictionary

Dictionary

• • Unordered collection of items / elements. Each item has two parts – key : value
     A mapping between key and it’s value, separated by colon (:)
     Items are enclosed in {} and separated by comma.
     Are optimized to retrieve data using key. So key (values) should be unique. They
    can be integer, float, string or tuple.
     D[key] can be used for accessing element, also to add element in an existing
    dictionary.

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    Creating dictionary

     Using assignment operator creates deep copy
     Using function
    1. dict()
    2. copy() creates shallow copy
    3. eval()
     {} to create blank dictionary

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    Dictionary method / function

     As key value is used to access elements, trying to retrieve an non existing key will
    result into error
     For adding elements in existing dictionary
                         dictionaryName[newKey] = value
                          If newKey matches to an existing key, then value gets updated.
     Del statement can be used to delete an element or entire dictionary
     len(), clear() method works for dictionary also
     keys() method can be used to get all key values existing the dictionary
     values() method can be used to get all values present in dictionary
     Items() method returns all key: value pairs as tuple. Which can then be used in
    for loop for processing

D = {1:’one’,2:’two’}
for i,j in D.items():
print(i,j)

 Converting a dictionary to list gives you a list of key values only.
 Get(key) method returns value mapped to the key
 Update(dictionary) method adds the elements of dictionary passed as argument
to existing dictionary
 pop(key) method removes the key:value mapping and returns the value removed
 popitem() method removes an arbitrary pair from dictionary

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Function/Method Purpose Example

len()- This function returns the number of elements i.e.the key-value pairs present in the dictionary.

>>>d={1: ‘Amrit’, 2: ‘Bhavesh’, 3: ‘Chetan’, 4: ‘Falguni’}
>>> len(d)
4

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d.items()- This function returns the list of elements in the dictionary.

>> d.items()
dict_items([(1, ‘Amrit’), (2,’Bhavesh’), (3, ‘Chetan’),(4, ‘Falguni’)])

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d.keys()- This function returns the all the keys that are present in the dictionary.

>> d.keys()
dict_keys([1, 2, 3, 4])

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d.values()- This returns all the values in the dictionary.

>> d.values()
dict_values([‘Amrit’,’Bhavesh’, ‘Chetan’,’Falguni’])

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d.get(key) -This function returns the value corresponding to a key in the dictionary. If the key is not present,

>>> d.get(2)
‘Bhavesh’

the function returns,
‘None’.

>> d.get(8, -1)
-1

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d.update(object)- This function merges the object enclosed in brackets with d.

>> d2={5: ‘Kartikay’, 6:
‘Prerna’}
>>> d.update(d2)
>>> d
{1: ‘Amrit’, 2: ‘Bhavesh’, 3:’Chetan’, 4: ‘Falguni’, 5:’Kartikay’, 6: ‘Prerna’}

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d.clear() -This function clears the entire dictionary. It deletes all the key-value pairs.

>>d2={1:”Deer”,2:”Bear”, 3:”Cat”,4:”Elephant”}
>>>d2
{1:”Deer”, 2:”Bear”,3:”Cat”, 4:”Elephant”}
>>>d2.clear()
>>>d2
{}

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d.pop(key)- This function removes a key along with its value in a dictionary.

>> d2={1:”Apple”,2:”Ball”,3:”Pineapple”,4:”Mangoes”}
>>> d2.pop(2)
‘Ball’
>>> d2
{1: ‘Apple’, 3: ‘Pineapple’,4: ‘Mangoes’}

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