DICTIONARIES - Python…
Dictionary என்பது Python-ல் data-ஐ key : value pair format-…
Dictionary என்பது Python-ல் data-ஐ key : value pair format-ல் store செய்ய பயன்படும் built-in collection data type. Simple example: student = { "name": "Arun", "age": 20, "mark": 85 } இதில்: "name" → "Arun" "age" → 20 "mark" → 85 Left side:…
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Definition
Dictionary என்பது Python-ல் data-ஐ key : value pair format-ல் store செய்ய பயன்படும் built-in collection data ……
Simple Explanation
List-ல் values index number ம……
Explanation
Example
student = ["Arun", 20, 85] இதில்: student[0] → Arun student[1] → 20 student[2] → 85 ஆனால் index 0, 1, 2 பார்த……
Explanation
Real world idea
ஒரு student record: Name = Arun Age = 20 Mark = 85 City = Chennai Python dictionary: ……
Flow
Dictionary-ஐ இப்படிப் புரிந்துகொள்ளுங்கள்: Dictionary ↓ Key : ……
Explanation
Example
student["mark"]…
Output
Result
Explanation
Basic syntax: dictionary_name……
Program
Example
Explanation
Dictionary uses: { } Curly braces. Each pair uses: : Co……
Explanation
student = { student என்ற dictionary உருவாக்குகிறோம். "name": "Kumar"……
Explanation
Key and value
Dictionary-ன் அடிப்படை concep……
Program
Example
Explanation
இதில்: brand → key Toyota → v……
Explanation
Accessing dictionary values
Dictionary value access செய்ய key பயன்படுத்த வேண்ட……
Program
Another
Important
Important difference from list
List: data = ["Python", 25] Access: data[0] Dictionary: data = { "la……
Explanation
Dictionary is mutable
Dictionary is mutable. Mutable means: ……
Program
Example
Explanation
student["mark"] = 95…
Old value: 80 New value: 95…
Explanation
Add new item
Existing dictionary-க்கு புதிய key-value pair add செய……
Important rule: If key does no……
Explanation
Update existing item
If key already exists: studen……
Program
Example
Explanation
student["age"] = 21…
Comparison
Add vs update
Same syntax: dictionary[key] = value But beha……
Explanation
Example
student["city"] = "Madurai" city இல்லை……
Explanation
Duplicate keys
Dictionary keys must be uniqu……
Program
Example
Why? Same key: "name" twice பயன்படுத்தப்பட்ட……
Important
Dictionary: Duplicate keys → ……
Program
Example
Explanation
Both values same. No problem.……
Explanation
Dictionary keys data types
Dictionary key commonly: String Integer Tuple போன்ற immutable typ……
Explanation
String key
Most commonly string key use செய்வோம். empl……
Explanation
Integer key
subjects = { 1: "Tamil", 2: "……
Important
subjects[1] works. But: subje……
Explanation
Values can have any type
Dictionary values can be almost any Python object. data = { "name": "Arun", "a……
Explanation
Empty dictionary
Empty dictionary: data = {} C……
Explanation
Dict function
Dictionary can also be created using dic……
Explanation
Type check
student = { "name": "Arun" } ……
Explanation
Len
len() gives number of key-value pairs. stud……
Why? Three pairs: name : Arun……
Explanation
Get method
Normally: student["name"] value……
Program
Example
Comparison
Square bracket vs get
This is very important. Suppose key not av……
Common Mistake
Error
KeyError But: print(student.g……
So: dictionary[key] → missing key cau……
Explanation
Get with default value
get() method-க்கு default value கொடுக்க……
Because "age" key இல்லை. Anot……
Explanation
Keys method
All keys get செய்ய: student = { "name": "Arun", "age": 20……
Explanation
Values method
All values: print(student.val……
Explanation
Items method
Both keys and values get செய்……
Notice: Each pair returned as a……
Remember
keys() → keys only values() →……
Explanation
For loop over dictionary
Dictionary loop மிகவும் important. student =……
Important
By default dictionary loop re……
Explanation
Why only keys
When writing: for x in student: Python treats it ……
Explanation
Loop through keys
Explicitly: for key in studen……
Explanation
Loop through values
for value in student.values()……
Explanation
Loop through items
Key and value both: for key, ……
This is one of the most impor……
Explanation
How items loop works
Suppose: student.items() produces pairs: ("name", "Arun") ("age", 20) ("mark", 90) Loop: for key, v……
Explanation
Execution: First pair: ("A", ……
Explanation
Print: A 10 Next: ("B", 20) U……
Explanation
Print: B 20 Final output: A 1……
Explanation
Check key exists
Use in. student = { "name": "……
Program
Another
Important
in checks keys, not values.…
Explanation
Check value
To check value: print("Arun" ……
Explanation
Not in
print("city" not in student)…
if city key is absent.…
Explanation
Remove item del
del removes an item using key. student = { "n……
Explanation
Pop method
pop() removes specified key and returns its value. stu……
Explanation
Popitem
popitem() removes the last inserted key-value pair. studen……
Returned value itself is a tu……
Explanation
Clear
Remove all items: student.cle……
Dictionary still exists, but ……
Explanation
Del dictionary
del student Entire variable is d……
Comparison
Clear vs del
clear() → removes all items → dictionary ……
Explanation
Update method
Multiple values add/update செய்ய: student = { ……
Explanation
Update existing key
student = { "name": "Arun", "mark……
Explanation
Copy
Dictionary copy: student = { "name": "Arun……
Important
a = student does not create an inde……
Program
Example
Explanation
b["mark"] = 100…
Because: a ──┐ ├── same dicti……
Explanation
Nested dictionary
Dictionary inside dictionary: students = { "student1": { "name": ……
Explanation
Access nested dictionary
print(students["student1"]["n……
Think step-by-step: students["student1"] r……
Explanation
Dictionary with list
Dictionary value can be a list. student = { "name……
Program
First mark
Explanation
Dictionary with tuple
student = { "name": "Arun", "subjects": ……
Explanation
Fromkeys
dict.fromkeys() creates dictionary from keys with same ……
Explanation
Setdefault
setdefault() checks a key. If key exists: ex……
Program
Example
Explanation
Setdefault existing key
student = { "name": "Arun", "age……
Why? age already exists. So e……
Explanation
Dictionary order
Modern Python dictionaries preserve insertion order. data = { "a": 1, "b": 2, "c": 3 } Iteration normally fol……
Explanation
Can we access by position
Suppose: student = { "name": "Arun", "age": 20 } This……
Program
Example
Here 0 is a key, not a positi……
Explanation
Hashable keys
Advanced important concept: Dictionary keys need to be hashable. Usually immutable objects can be keys. Valid……
Common Mistake
Error
TypeError: unhashable type: '……
Explanation
Tuple as key
Tuple can be a dictionary key……
Program
Example
Explanation
Dictionary comprehension
Similar to list comprehension……
Program
Example
Definition
Meaning
Key → x Value → x*x…
Dry Run
Dry run dictionary comprehension
Comparison
List vs tuple vs set vs dictionary
Important
Important methods
Main dictionary methods: keys() values() items() get() update() pop……
Common Mistake
Common error 1
Wrong key: student = { "name"……
Common Mistake
Error
KeyError: 'age' Better: print……
Common Mistake
Common error 2
Wrong assumption: data = {"a": 10, "b": 20} print(data[0]) ……
Common Mistake
Common error 3
Duplicate key: data = { "x": 10, "……
Common Mistake
Common error 4
List as key: data = { [1, 2]:……
Common Mistake
Error
TypeError: unhashable type: '……
Common Mistake
Common error 5
Do not confuse: {} with empty set. Actual……
Empty set requires: set() Thi……
Memory Trick
Dictionary remember செய்ய: Dictionary = Word me……
Explanation
Example
"name" → "Arun" "age" → 20 So……
TRB Point
What is the output? d = { "a"……
TRB Point
Trb point 2
d = { "x": 1, "x": 2 } print(……
Reason: Dictionary keys must ……
TRB Point
Trb point 3
d = { "a": 10, "b": 20 } for ……
Important
Default dictionary iteration ……
TRB Point
Trb point 4
What does items() return? d.items() Concep……
TRB Point
Trb point 5
What is: type({}) Answer: Not……
TRB Point
Trb point 6
What is: type(set()) Answer:…
Interview Point
Why dictionary access is fast? Python dictionaries use a hash table internally. When a key is provided: stude……
Interview Point
Interview point 2
Can dictionary keys be mutable? Generally, mutable types like list cannot be keys be……
Interview Point
Interview point 3
Difference between get() and []? d["key"] Missi……
MCQ
Which symbol is used for dict……
MCQ
Dictionary stores data as:…
MCQ
What is the output? d = {"nam……
MCQ
What happens? d = {"a": 1} pr……
MCQ
What is the output? d = {"a":……
MCQ
What is the output? d = {"a":……
MCQ
Which method returns keys?…
MCQ
Which method returns values?…
MCQ
What does items() provide?…
MCQ
What is the output? d = { "a"……
MCQ
What is the type? x = {} prin……
MCQ
Which creates an empty set?…
MCQ
Dictionary keys are generally:…
MCQ
Dictionary values:…
Mcq 15
What is the output? d = {"x": 1……
Practice
Practice 1
Predict output: student = { "name":……
Practice
Practice 2
Predict: data = { 1: "A", 2: ……
Practice
Practice 3
Predict: d = { "a": 10, "b": ……
Practice
Practice 4
Predict: d = { "a": 10, "b": ……
Practice
Practice 5
Predict: d = { "a": 1, "b": 2……
Summary
Dictionary என்பது Python-ல் data-ஐ: key : value pairs-ஆக store செய்யும்……
Main methods: keys() values() items() get() update() pop() popitem() clear() copy() Most important rules: Dic……
Explanation
Short description
Dictionary = Key-based mutable collection of key-value pairs. Easy memory: List → Index : Value Dictionary → ……
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