Dictionary Datatype || Python for Beginners

 Dictionary

Definition

• A dictionary is an unordered collection of key-value pairs which are separated by a colon (:) and enclosed in a curly braces {}. A dictionary may contain any datatype and is mutable.

Example: 

dict1={‘Name’:‘Mari’, ‘Dept’:‘Mech’}

• A dictionary is used as a container for storing, managing and retrieving data in a key-value format.

Dictionary creation

• A dictionary may contain any datatype and is mutable

Syntax:

dict={}

dict={key1:value1, key2:value2, key3:value3}

• Where dict is the dictionary name.
• Key is user defined variable name.
• Values are assigned for key

Dictionary accessing

We can’t use indexing to access because dictionaries are unordered data type. Values stored in a dictionary can only be accessed through keys.

Example: 

dict1={‘Name’:‘Mari’, ‘Dept’:‘Mech’}

dict1[‘Name’]

dict1[‘Dept’]

Output:

‘Mari’

‘Mech’

Dictionary updation 

• To add a new key-value pair, the assignment (=) operator can be used.

Syntax:

dict[key]=value

Example:

dict1={‘Name’:‘Mari’, ‘Dept’:‘Mech’}

dict1[‘Age’]=19

dict1

Output:

{‘Name’:‘Mari’, ‘Dept’:‘Mech’, ‘Age’:19}

• To modify the current value, use the assignment operator(=) can be used.

Syntax:

dict[key]=value

Example:

dict1={‘Name’:‘Mari’, ‘Dept’:‘Mech’}

dict1[‘Dept’]=‘CSE’

dict1

Output:

{‘Name’:‘Mari’, ‘Dept’:‘CSE’}

Dictionary methods

• dict.update()
• dict.items()
• dict.values()
• dict.keys()
• dict.setdefault()
• dict.copy()
• dict.fromkeys()
• dict.pop()
• dict.popitem()
• dict.clear()
• del keyword

(i) dict.update(dict)

Updates a dictionary with key-value pairs from another dictionary

 Syntax

dict.update(dict)

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict2={'Place':'Tuticorin', 'Dept':'CSE'}

dict1.update(dict2)

dict1

Output

{'Name':'Mari', 'Dept':'CSE', 'Age':19, 'Place':'Tuticorin'}

 

(ii) dict.items()

Returns list of dictionary key-value pair

Syntax

dict.items()

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.items()

Output

dict_items([('Name', 'Mari'), ('Dept', 'Mech'), ('Age', 19)])

(iii)dict.values()

Returns list of a dictionary values.

Syntax

dict.value()

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.values()

Output

dict_values(['Mari', 'Mech', 19])

(iv) dict.keys()

Returns list of a dictionary keys.

Syntax

dict.keys()

Example 

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.keys()

Output

dict_keys(['Name', 'Dept', 'Age'])

(v) dict.setdefault()

Searches a given keys in a dictionary and returns the value if found.

Syntax

dict.setdefault(key, default=None) 

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.setdefault('Dept', None)

Output

'Mech'

(vi) dict.copy()

Returns a copy of a dictionary

Syntax

dict.copy()

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict3=dict1.copy()

dict2['Dept']='CSE'

dict1

dict3

Output

{'Name':'Mari', 'Dept':'Mech', 'Age':19}

{'Name':'Mari', 'Dept':'CSE', 'Age':19}

(vii) dict.fromkeys()

Creates dictionary from given sequence.

Syntax

dict.fromkeys(key, value)

Example

keys=['apple', 'orange', 'mango']

dict4=dict.fromkeys(keys, 10) 

dict4

Output

{'apple':10, 'orange':10, 'mango':10}

(viii) dict.pop()

Removes the random pair and returns the deleted key-value pair.

syntax

dict.pop(key)

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.pop('Dept')

dict1

Output

Mech

{'Name':'Mari', 'Age':19}

(ix) dict.popitem()

Removes the random pair and returns the deleted key-value pair.

 Syntax

dict.popitem()

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.popitem()

dict1

Output

('Age', 19)

{'Name':'Mari', 'Dept':'Mech'}

(x) dict.clear()

Removes all the key-value pairs.

Syntax

dict.clear()

Example

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

dict1.clear()

dict1

Output

{}

(xi) del keyword

Used to delete a dictionary.

Syntax

del dictname

Example 

dict1={'Name':'Mari', 'Dept':'Mech', 'Age':19}

del dict1

dict1

Output

Error