Dictionary in Python

1) Dictionary Concept in Python

A Dictionary stores elements in the form of key : value pairs. The key provides identity, and the value contains the actual data.

Example: For storing student records, rollno can act as the key and 1001 as the value.

Syntax of Dictionary

var = {key:value, key:value, ...}

Stu = {"rno":1001, "sname":"manish kumar", "branch":"CS", "fees":45000}

Here, rno, sname, branch, fees are keys and 1001, "manish kumar", "CS", 45000 are values.

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Dictionaries maintain sequence internally (Python 3.7+). They are an enhancement of Set objects and provide faster searching than Lists. They are mutable — we can add, edit, or delete items dynamically.

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Program to Display Only Keys

x = {"rno":1001, "sname":"manish kumar", "branch":"cs", "fees":15000}

for key in x:
    print(key)

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Program to Display Only Values

x = {"rno":1001, "sname":"manish kumar", "branch":"cs", "fees":15000}

for key in x:
    print(x[key])

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Program to Display Key and Value

Method 1:

x = {"rno":1001, "sname":"manish kumar", "branch":"cs", "fees":15000}

for key in x:
    print(key, x[key])

Method 2 (Best Method):

for k, v in student.items():
    print(k, " ", v)

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Dictionary is Mutable — Add / Edit / Delete Example

x = {"rno":1001, "sname":"manish kumar", "branch":"cs", "fees":15000}

x["rno"] = 1002            # modify
del x["rno"]               # delete
x.update({'sem':'3rd'})    # add new key-value

for key in x:
    print(key, x[key])

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Input from Users in Dictionary

x = {}

item = int(input("enter number of items in dictionary"))

for i in range(0, item):
    key = input("enter key")
    value = input("enter value")
    x.update({key:value})

print(x)

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WAP to Reverse Dictionary Elements

stu = {"rno":1001, "sname":"manish kumar", "branch":"CS", "fees":45000}

stu["rno"] = 1002
del stu["rno"]
stu.update({"fees":55000})
stu.update({"sem":"vth"})

l = []
for k in stu:
    print("key is ", k, " and value is ", stu[k])
    l.append(k)

for i in range(len(l)-1, -1, -1):
    print("key is ", l[i], " and value is ", stu[l[i]])

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WAP to Display Dictionary in Reverse Dictionary Format

s = {"empid":"Kang1001", "empid":"Kang1001", "empname":"jay kumar",
     "deptname":"Sales", "Salary":45000}

key = []
val = []

for d in s:
    key.append(d)
    val.append(s[d])

res = "{"

for i in range(len(key)-1, -1, -1):
    if i != 0:
        res = res + str(key[i]) + ":" + str(val[i]) + ","
    else:
        res = res + str(key[i]) + ":" + str(val[i])

res = res + "}"

print(res)

for data in s:
    print(data, s[data])

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WAP to Find Max Value in Dictionary

d = {"A":12, "C":34, "B":11, "E":78, "F":22}

m = 0

for item in d:
    if m < d[item]:
        m = d[item]

print("max value is ", m)

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WAP to Find Max Key in Dictionary

(Keys compared alphabetically)

max_key = max(d.keys())
print("max key is ", max_key)

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WAP to Convert Dictionary to Set

You can convert:

• Keys → set(d.keys())
• Values → set(d.values())
• Items → set(d.items())

d = {"A":12,"C":34,"B":11,"E":78,"F":22}

key_set = set(d.keys())
value_set = set(d.values())
item_set = set(d.items())

print(key_set)
print(value_set)
print(item_set)