keys of dictionary must be of immutable types

creating a dictionary

dict={"1":"raman","2":"gagan","3":"aman"};
print(dict);

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access elements of dictionary using a key

dict={"1":"raman","2":"gagan","3":"aman"};
print(dict["2"]);

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attempting to access a key that does not exist results in an error

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traversing a dictionary using keys

dict={"1":"raman","2":"gagan","3":"aman"};
for key in dict:
    print(dict[key]);

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traversing a dictionary and printing key value pairs and items function

dict={"1":"raman","2":"gagan","3":"aman"};
for key,val in dict.items():
    print(key ,":", val);

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program to create a phone dictionary and print it

dict={"raman":"25997888","gagan":"25595652","aman":"23344556"};
for name in dict:
    print(name, ":", dict[name]);

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printing keys using keys method

dict={"raman":"25997888","gagan":"25595652","aman":"23344556"};
print(dict.keys());

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printing values using values method

dict={"raman":"25997888","gagan":"25595652","aman":"23344556"};
print(dict.values());

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initialize a dictionary

dict={"raman":"25997888","gagan":"25595652","aman":"23344556"};
print(dict);

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add key value pairs

dict={"raman":"25997888","gagan":"25595652","aman":"23344556"};
print(dict);
dict["manpreet"]="8888888";
print(dict);

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creating dictionary from name and value pairs

dict=dict(name='raman',age=18,salary=90000);
print(dict);

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creating dictionary by specifying comma separated key value pairs

dict=dict({'name':'raman','age':18,'salary':90000});
print(dict);

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creating a dictionary by specifying keys separately and corresponding values separately

dic=dict(zip(('name','age','salary'),('raman',18,90000)));
print(dic);

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creating a dictionary by specify key value pairs separately in the form of sequences.

dic=dict([['name','raman'],['age',18],['salary',90000]]);
print(dic);

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add elements to dictionary

dic={"name":"raman","age":18,"salary":90000};
print(dic);
dic["designation"]="accountant";
print(dic);

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example of nested dictionary

dic={"raman":{"age":18,"salary":90000},"gagan":{"age":20,"salary":80000}};
print(dic);

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traversing a nested dictionary

dic={"raman":{"age":18,"salary":90000},"gagan":{"age":20,"salary":80000}};
for key in dic:
    print("employee",key,":")
    print("age : ",str(dic[key]['age']))
    print("salary : ",str(dic[key]['salary']))

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update existing element

dic={"name":"raman","age":19,"salary":90000};
print(dic);
dic['age']=23;
print(dic);

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delete element from dictionary using key

dic={"name":"raman","age":19,"salary":90000};
print(dic);
del dic['age'];
print(dic);

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pop element from dictionary using pop method

dic={"name":"raman","age":19,"salary":90000};
a=dic.pop("age");
print(a);

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pop element from dictionary if not found show error

dic={"name":"raman","age":19,"salary":90000};
a=dic.pop("designation",'not found');
print(a);

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check key in dictionary

dic={"name":"raman","age":19,"salary":90000};
print("age" in dic);

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check key not in dictionary

dic={"name":"raman","age":19,"salary":90000};
print("age" not in dic);

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print json form of dictionary

import json;
dic={"name":"raman","age":19,"salary":90000};
print(json.dumps(dic,indent=2));

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count frequency of elements in a list using dictionary

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dictionary methods

len method

dic={"name":"raman","age":19,"salary":90000};
print(len(dic));

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clear method

dic={"name":"raman","age":19,"salary":90000};
print(dic);
dic.clear();
print(dic);

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delete a dictionary

dic={"name":"raman","age":19,"salary":90000};
print(dic);
del dic;
print(dic);

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get method

dic={"name":"raman","age":19,"salary":90000};
print(dic.get("age"));

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show an error if key not found

dic={"name":"raman","age":19,"salary":90000};
print(dic.get("designation","designation not found"));

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items() method


dic={"name":"raman","age":19,"salary":90000};
for key,val in dic.items():
    print(key ,":",val);

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keys method

dic={"name":"raman","age":19,"salary":90000};
for key in dic.keys():
    print(key);

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values method

dic={"name":"raman","age":19,"salary":90000};
for val in dic.values():
    print(val);

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update method merges key value pairs from the new dictionary into the original dictionary


dic={"name":"raman","age":19,"salary":90000};
dic1={"designation":"accountant"};
print(dic);
dic.update(dic1);
print(dic);
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program to count frequency of elemnts in list using dictionary

freq = {}
my_list=["raman","deep","deep","singh","raman"];
for item in my_list:
    if (item in freq):
        freq[item] += 1
    else:
        freq[item] = 1
for key, value in freq.items():
    print ("%s : %d"%(key, value));
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