Python Ninja Bootcamp 8-Dictionary

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In this Python lecture, we will learn about the Dictionary.

"Dictionary is an unordered collection of items i.e key-value pairs ".

Let's look at Dictionary example-

Create Dictionary

Dictionary is defined by placing item i.e key-value pair, inside curly braces {} separated by a comma. Each key is separated from its value by a colon (:).

my_dictionary = { 'key1': 1 ,'key2': 2 ,'key3': 3 } # here key Key1, key2 & key3 is mapped with the value 1, 2 & 3 repectively

print(my_dictionary)

>> { 'key1' : 1, 'key2' : 2, 'key3' : 3 }

Access Dictionary Values

We can use the key inside the index operator [] to access a value in a dictionary. 

my_dictionary = { 'key1': 1 ,'key2': 2 ,'key3': 3 }

print( my_dictionary['key1'] ) # garbs the value mapped with key1

>>1

We have an option in python that list can hold different object type (integer, float, string etc).

my_dictionary={ 'key1': 1, 'key2': 1.5,'key3': 'string'}

print( my_dictionary )

>>{ 'key1': 1, 'key2': 1.5 ,'key3': 'string' }

my_dictionary={ 'key1': 1, 'key2': 1.5,'key3': 'string'}

print( my_dictionary['key3'] )

>> 'string' 

Since the value corresponding to key3 is a string object, so we can perform all thing we did in string lecture. 

print( my_dictionary['key3'][0] ) # grab the letter at index 0

>> 's'

print( my_dictionary['key3'][-1] ) # reverse the string

>> gnirts

print( my_dictionary['key3'].upper( ) ) # Convert the string to uppercase

>> STRING

Mutability

Dictionary is mutable, the values within it can be changed or replaced, unlike string or tuple.

We can use the assignment operator (=) to change an item or a range of items.

my_dictionary={ 'key1': 1, 'key2': 1.5,'key3': 'string'}

my_dictionary['key1'] = my_dictionary['key1'] + 99

print( my_dictionary['key1'] )

>> 100

print( my_dictonary )

>> { 'key1': 100, 'key2': 1.5,'key3': 'string'}

We can also use subtraction to change the 'key1' value 

my_dictionary['key1'] - = 50

print( my_dictionary['key1'] )

>> 50

print( my_dictionary )

>> { 'key1': 50, 'key2': 1.5,'key3': 'string'}

Another Method of Creating Dictionary 

We can also create a dictionary with an empty dictionary

# Create a empty dictionary

d = {}

print( d )

>> { }

# Insert the key-value pairs in the empty dictionary

d['student' ] = 'Tamta'

d['roll_no'] = 40

print( d )

>> { 'student' : 'Tamta' , 'roll_no' : 40 }

Nested dictionary

Dictionary could have another dictionary as a key-value pair. This is called a nested dictionary.

d = {'key' : {'nestedkey' : {'subnestedkey' : 'value' }}}
print( d )

>> {'key': {'nestedkey': {'subnestedkey': 'value'}}}

We can use keys to extract the value in the nested list.

Let's see how to grab the value.

# keep calling the keys

print( d['key']['nestedkey']['subnestedkey'] ) 

>> 'value'

Since the value is a string object, so we can perform all thing we did in string lecture. 

print( d['key']['nestedkey']['subnestedkey'].upper( ) ) 

>> VALUE

Built-in Function

Methods that are available with Dictionary.

d = { 'k1' : 1, 'k2': 2, 'k3': 3} 

print( d )

>> {  'k1' : 1, 'k2': 2, 'k3': 3 }

Note: If press TAB after d. in the Juypter notebook. It will show the list of functions available in the string.

print( d.keys() )  # Return a new view of the dictionary's keys.

>> dict_keys( ['k1', 'k2', 'k3'] )

print( d.values() ) # Return a new view of the dictionary's values.

>> dict_values( [1, 2, 3] )

print( d.items() ) # Return a new view of the dictionary's key-value pair.

>>dict_items( [('k1', 1), ('k2', 2), ('k3', 3)] )

d.pop( 'k1' )  # remove specified key and return the corresponding value

print( d )

>>{ 'k2': 2, 'k3' : 3}

d.clear() # remove all the items from the dictionary

print(d)

>>{ }

Practice other built-in functions available in the list.

EDITS ARE WELCOMED!!

In the next Blog, we will discuss Tuple 

https://sngurukuls247.blogspot.com/2018/09/python-ninja-bootcamp-9-tuple.html


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