Dictionary Operations
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Dictionary Methods:
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How to define the dictionary in the run time:
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eval()
=======
-> to create any collection dynamically, we can use "eval()".
Syntax:
	collection-name = eval(input("some text"))

d = eval(input("Enter a dictionary:"))

print("The Given dictionary = ",d)

How to delete the data from the dictionary:
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1) pop():
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-> pop() can accept the key
-> with the reference of the key, pop() can delete that specified value (value which is associated with the given key)
Syntax:
	dictionary-name.pop(key)
-> pop() can return a value which is deleting based on the key.

d = eval(input("Enter a dictionary:"))

print("The Given dictionary = ",d)

x = d.pop('a')

print("The Dictionary after the pop operation = ",d)
print(x)

d.pop('p')

print(d)

-> pop() can give a run time error "key error", when the specified key is not in the given dictionary.

2) popitem():
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-> popitem() not accept any key as parameter.
-> it can able to delete the last item (key-value pair) from the dictionary.
-> popitem() can return "that item (which is going to delete)"
-> when we can define popitem() on empty dictionary, we can get "key error".

d = {'apple':121,'banana':112,'cherry':123,'mango':1023}
d1 = {}

print("The Original Dictionary = ",d)

x = d.popitem()
# d1.popitem()
# d1.pop(1)

print("The Dictionary after the delete operation = ",d)
print(x)

print(d1)

3) del operator
===============
-> del operator can use to delete the specific key-value pair.
Syntax:
	del dictionary-name[key]
-> del operator can also use to delete the whole dictionary permanently.
Syntax:
	del dictional-name
-> Once the deletion is completed,
	then, we cannot access it.	
	If you can use to access, we can get "name error".

d = {'apple':121,'banana':112,'cherry':123,'mango':1023}

print("The Original Dictionary = ",d)

del d['cherry']

print("The Dictionary after the delete operation is = ",d)

del d

print(d)

4) clear()
==========
-> clear() can clear/delete/remove all key-value pairs from the dictionary.
-> after the clear we can able to print an empty dictionary.

Syntax:
	dictionary-name.clear()

d = {'apple':121,'banana':112,'cherry':123,'mango':1023}

print("The Original Dictionary = ",d)

# d.clear('apple')
d.clear()

print(d)
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items():
=======
Syntax:
	dictionary-name.items()

-> items() can return list of tuples
Each tuple is an arbitrary with key-value.

d = {'apple':121,'banana':112,'cherry':123,'mango':1023}

print("The Original Dictionary = ",d)

x = d.items()

print(x)

for i in x:
  print(i)	

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keys():
=======
Syntax:
	dictionary-name.keys()
-> to get only the keys from the dictionary, we can use "keys()".

d = {'apple':121,'banana':112,'cherry':123,'mango':1023}

print("The Original Dictionary = ",d)

x = d.keys()

print(x)

for i in x:
  # print(i)
  # print(d[i])
  print(i,":",d[i])

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values()
========
Syntax:
	dictionary-name.values()

d = {'apple':121,'banana':112,'cherry':123,'mango':1023}

print("The Original Dictionary = ",d)

x = d.values()

print(x)

for i in x:
  print(i)
===================================================
Comprehensions:
==============
-> It is a shorter way/syntax which can be used to create a collection based on the values of existing collection.
-> For immutable collections, comprehension is not allowed.
-> So, there are three collections only in python which support the comprehensions.
	1) List Comprehensions
	2) Set Comprehensions
	3) Dictionary Comprehensions

1) List Comprehensions
======================
Syntax:
	new_List = [Output_Expression for variable in Input_Expression if(variable satisfies the condition)]

# creating a list from existing

listData = ["apple","banana","cherry","kiwi","mango"]
newList = []

# traditional way
for i in listData:
  if 'a' in i:
    newList.append(i)

print(newList)


# using List comprehensions
newList = [x for x in listData if "a" in x]

print("The Original list = ",listData)
print("The New List = ",newList)

====================
listData = [1,2,3,4,5,6,7,8]

dictionary = {var:var ** 3 for var in listData if var % 2 != 0}

print(dictionary)