collection data type: dict

dict

• Dictionary can be created by using curly brackets {}or  by calling dict() function

• Dictionary represents group of key-value pairs. Each key-value pair in the dictionary is known as an item.

• Dictionary is a mutable object.

• Keys must be immutable objects.

• values can be mutable objects or immutable objects.

• Insertion order is not preserved.

• Duplicate keys are not allowed but values can be duplicate.

• Heterogeneous key and values are allowed.

x={}

print(x)

print(type(x))

{ }

<class 'dict'>

y=dict()

print(y)

print(type(y))

{ }

<class 'dict'>

z={ 'JAVA':90,'hadoop':85,'python':89 }

print(z)

print(type(z))

{ 'python': 89, 'hadoop': 85, 'JAVA': 90 }

<class 'dict'>

a={ 'java':90,10:'hyd',True:1234,20:'hyd',30:[1,2,3],'java':95 }

print(a)

{ True: 1234, 'java': 95, 20: 'hyd', 10: 'hyd', 30: [1, 2, 3] }

b={'hyd':40,'bang':20,'Delhi':15}

print(b)

b['chennai']=42

print(b)

{ 'hyd': 40, 'bang': 20, 'Delhi': 15 }

{ 'chennai': 42, 'hyd': 40, 'bang': 20, 'Delhi': 15 }

print(b['hyd'])

40

c={'hyd':40,'bang':20,'Delhi':15}

print(c)

k=c.keys();

for p in k:

         print(p)

v=c.values();

for q in v:

         print(q)

{'bang': 20, 'Delhi': 15, 'hyd': 40}

bang

Delhi

hyd

20

15

40

Python Dictionary Methods

Python Dictionary Methods
Method	Description
clear()	Remove all items form the dictionary.
copy()	Return a shallow copy of the dictionary.
fromkeys(seq[, v])	Return a new dictionary with keys from seq and value equal to v (defaults to None).
get(key[,d])	Return the value of key. If keydoesnot exit, return d (defaults toNone).
items()	Return a new view of the dictionary's items (key, value).
keys()	Return a new view of the dictionary's keys.
pop(key[,d])	Remove the item with key and return its value or d if key is not found. If d is not provided andkey is not found, raisesKeyError.
popitem()	Remove and return an arbitary item (key, value). Raises KeyErrorif the dictionary is empty.
setdefault(key[,d])	If key is in the dictionary, return its value. If not, insert key with a value of d and return d (defaults to None).
update([other])	Update the dictionary with the key/value pairs from other, overwriting existing keys.
values()	Return a new view of the dictionary's values

d={'java':90,'python':98,'hadoop':85,'oracle':90}

print(d)

print(d['python'])

print(d.get('hadoop'))

d.pop('oracle')

print(d)

print(d.popitem())

print(d)

d.clear()

print(d)

{'java': 90, 'oracle': 90, 'python': 98, 'hadoop': 85}

98

85

{'java': 90, 'python': 98, 'hadoop': 85}

('java', 90)

{'python': 98, 'hadoop': 85}

{ }

marks={}

e=marks.fromkeys(['Math','English','Science'],10)

print(e)

{'Science': 10, 'English': 10, 'Math': 10}

marks={}

f=marks.fromkeys(['Math','English','Science'],[10,20,30])

print(f)

{'Science': [10, 20, 30], 'English': [10, 20, 30], 'Math': [10, 20, 30]}

Dictionary Comprehension:

x={p:p**2 for p in range(10)}

print(x)

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}

y={q:q**q for q in range(5)}

print(y)

{0: 1, 1: 1, 2: 4, 3: 27, 4: 256}

z={r:r*2 for r in range(10) if r%2==0}

print(z)

{0: 0, 8: 16, 2: 4, 4: 8, 6: 12}