Chapter 7: Python Data Structures

Python List - Basic Samajh

List ek ordered collection hoti hai jisme hum multiple items store kar sakte hain. Items kisi bhi type ke ho sakte hain - int, str, float, etc.

Banane ka Tarika:

my_list = [10, 20, 30, "hello", 5.5]

Access Karna:

    print(my_list[0])  # 10

    print(my_list[3])  # hello

10
hello

2. append() Method

Meaning: append() ka matlab list ke end me ek naya element add karna.

Syntax:

list_name.append(element)

Correct Example:

    fruits = ["apple", "banana"]

    fruits.append("mango")

    print(fruits)

['apple', 'banana', 'mango']

Galat Example:

    fruits = ["apple"]

    fruits.append("banana", "mango")  # ❌ append sirf ek item le sakta hai

3. insert() Method

Meaning: Kisi specific position par item insert karna.

Syntax:

list_name.insert(index, element)

    fruits = ["apple", "mango"]

    fruits.insert(1, "banana")

    print(fruits)

['apple', 'banana', 'mango']

4. remove() Method

Meaning: List me se koi specific item (value) ko hataana.

Syntax:

list_name.remove(value)

    fruits = ["apple", "banana", "mango"]

    fruits.remove("banana")

    print(fruits)

['apple', 'mango']

Common Mistake:

fruits.remove("orange") # ❌ ValueError: orange list me hai hi nahi

5. pop() Method

Meaning: List se item nikaalo aur return bhi karo. Default last item ko pop karta hai.

Syntax:

    item = list_name.pop()  # last item

    item = list_name.pop(index)  # specific index

    nums = [10, 20, 30]

    x = nums.pop()

    print(x)

    print(nums)

30
[10, 20]

6. sort() Method

Meaning: List ko ascending (ya descending) order me arrange karna.

Syntax:

    list_name.sort()  # ascending

    list_name.sort(reverse=True)  # descending

    nums = [5, 2, 9, 1]

    nums.sort()

    print(nums)

[1, 2, 5, 9]

Descending:

    nums.sort(reverse=True)

    print(nums)

[9, 5, 2, 1]

7. Summary Table of List Methods

append(x) – List ke end me x add karta hai
insert(i, x) – Position i pe x insert karta hai
remove(x) – First occurrence of x ko hataata hai
pop([i]) – i-th element ko remove karta hai aur return karta hai
sort() – List ko sort karta hai (ascending by default)

Python Tuples - Samajh Aur Use

Tuple bhi ek ordered collection hota hai jaise list, lekin immutable hota hai. Iska matlab: banane ke baad usme koi change (add, remove, update) nahi kar sakte.

Tuple Banane ka Tarika:

    my_tuple = (10, 20, 30)

    empty_tuple = ()

    one_item_tuple = (5,)  # Note: comma zaroori hai

Access Karna (Indexing):

    print(my_tuple[0])

    print(my_tuple[2])

10
30

Tuple Immutability Example:

    my_tuple[1] = 50  # ❌ TypeError: 'tuple' object does not support item assignment
  

Tuple ke Saath Looping:

    for item in my_tuple:

        print(item)

10
20
30

Why Use Tuples?

Data ko fixed rakhna ho (jaise coordinates, config settings)
Faster than list (thoda performance better hota hai)
Can be used as dictionary keys (lists nahi ho sakte)

Common Mistake:

    one_item = (5)  # ❌ This is int, not tuple

    print(type(one_item))  # Output: <class 'int'>

Correct Way:

    one_item = (5,)

    print(type(one_item))  # Output: <class 'tuple'>

Python Sets - Unordered Unique Collection

Set ek aisi collection hoti hai jisme unique elements hote hain. Iska order fixed nahi hota (unordered), aur indexing allowed nahi hai.

Set Banane ka Tarika:

    my_set = {1, 2, 3, 4}

    mixed_set = {"apple", 100, True}

    empty_set = set()  # ❌ {} likhne se empty dict banta hai

Set Me Duplicate Nahi Hota:

    dup = {1, 2, 2, 3}

    print(dup)  # Output: {1, 2, 3}

{1, 2, 3}

Common Mistake (Indexing Try Karna):

    my_set = {10, 20, 30}

    print(my_set[0])  # ❌ Error: 'set' object is not subscriptable

Set me Values Add Karna - `add()`:

    s = {1, 2}

    s.add(3)

    print(s)

{1, 2, 3}

Remove vs Discard:

    s = {1, 2, 3}

    s.remove(2)   # 2 hat gaya

    s.discard(5)  # 5 nahi tha, lekin error nahi aaya

Wrong Use of `remove()`:

    s = {1, 2, 3}

    s.remove(5)  # ❌ KeyError: 5 not found

Set Operations:

union() - Do sets ka combined result
intersection() - Common elements
difference() - Jo ek set me hai dusre me nahi

    a = {1, 2, 3}

    b = {3, 4, 5}

    print(a.union(b))         # {1, 2, 3, 4, 5}

    print(a.intersection(b))  # {3}

    print(a.difference(b))    # {1, 2}

{1, 2, 3, 4, 5}
{3}
{1, 2}

Looping through Set:

    for item in {"apple", "banana", "mango"}:

        print(item)

Important Notes:

Sets unordered hote hain — same order me print nahi hota
Indexing, slicing allowed nahi hai
Only immutable (unchangeable) elements allowed — list inside set ❌

Python Dictionaries - Key-Value Ka Magic

Dictionary ek aisa data structure hai jo key-value pairs me data store karta hai. Har key unique hoti hai, aur uske saath ek value jodi hoti hai.

Dictionary Banane ka Tarika:

    student = {

      "name": "Ravi",

      "age": 21,

      "grade": "A"

    }

    print(student["name"])  # Output: Ravi

Ravi

Empty Dictionary:

    empty = {}

    print(type(empty))  # Output: <class 'dict'>

Key-Value Access & Update:

    student["age"] = 22  # value update

    student["city"] = "Delhi"  # new key-value add

    print(student)

{'name': 'Ravi', 'age': 22, 'grade': 'A', 'city': 'Delhi'}

Access Karne ke Rules:

Key case-sensitive hoti hai ("Name" ≠ "name")
Agar key exist nahi karti aur access kiya to ❌ KeyError aata hai

❌ Wrong Access:

    student = {"name": "Amit"}

    print(student["age"])  # ❌ Error: 'age' key nahi hai

✅ Safe Access with `get()`:

    print(student.get("age", "Not Found"))

    print(student.get("name", "Not Found"))

Not Found
Amit

Important Methods:

get() – safely value access karta hai
keys() – sabhi keys ka list deta hai
values() – sabhi values deta hai
items() – sabhi key-value pairs as tuples deta hai
update() – ek dict me doosri dict ke items add/overwrite karta hai
pop() – kisi key ko hata kar uski value return karta hai

Examples:

    person = {"name": "Asha", "age": 30}

    print(person.keys())

    print(person.values())

    print(person.items())

    person.update({"city": "Mumbai"})

    print(person)

    person.pop("age")

    print(person)

dict_keys(['name', 'age'])
dict_values(['Asha', 30])
dict_items([('name', 'Asha'), ('age', 30)])
{'name': 'Asha', 'age': 30, 'city': 'Mumbai'}
{'name': 'Asha', 'city': 'Mumbai'}

Looping Over Dictionary:

    for key, value in person.items():

      print(key, "=>", value)

name => Asha
city => Mumbai

Note:

Keys unique hoti hain, values duplicate ho sakti hain
Keys immutable types hi ho sakti hain (string, number, tuple)
Nested dictionaries bhi possible hain

Nested Dictionary:

    student = {

      "name": "Ravi",

      "marks": {"math": 90, "science": 95}

    }

    print(student["marks"]["science"])  # Output: 95

Python List - Basic Samajh

Banane ka Tarika:

Access Karna:

2. append() Method

Syntax:

Correct Example:

Galat Example:

3. insert() Method

Syntax:

4. remove() Method

Syntax:

Common Mistake:

5. pop() Method

Syntax:

6. sort() Method

Syntax:

Descending:

7. Summary Table of List Methods

Python Tuples - Samajh Aur Use

Tuple Banane ka Tarika:

Access Karna (Indexing):

Tuple Immutability Example:

Tuple ke Saath Looping:

Why Use Tuples?

Common Mistake:

Correct Way:

Python Sets - Unordered Unique Collection

Set Banane ka Tarika:

Set Me Duplicate Nahi Hota:

Common Mistake (Indexing Try Karna):

Set me Values Add Karna - add():

Remove vs Discard:

Wrong Use of remove():

Set Operations:

Looping through Set:

Important Notes:

Python Dictionaries - Key-Value Ka Magic

Dictionary Banane ka Tarika:

Empty Dictionary:

Key-Value Access & Update:

Access Karne ke Rules:

❌ Wrong Access:

✅ Safe Access with get():

Important Methods:

Examples:

Looping Over Dictionary:

Note:

Nested Dictionary:

Set me Values Add Karna - `add()`:

Wrong Use of `remove()`:

✅ Safe Access with `get()`: