Great.
DAY 5 is where Python stops looking like a collection of keywords and starts looking like a coherent object system.

After today, you’ll never be confused by type, object, None, or “truthy / falsy” behavior again.

🧠 DAY 5 — Built-in Data Types: The Big Picture (Python Object Model)

🔑 CORE IDEA OF DAY 5

In Python, EVERYTHING is an object — including types, functions, and classes.

There are no primitives in Python.

1️⃣ The Python Object Universe (One Diagram to Rule Them All)

At the top of Python’s universe:

object
   ↑
 type
   ↑
int, str, list, dict, function, class, module, ...

Yes — type itself is an object, and type inherits from object.

2️⃣ The Holy Trinity: object, type, Instances

This triangle is interview gold.

Observe carefully:

x = 10

type(x)        # int
type(int)      # type
type(type)     # type
issubclass(int, object)  # True

Meaning:

• object → base class of everything
• type → class that creates classes
• Classes are objects too

🧠 Python is a meta-circular object system

3️⃣ What Is an Object Internally? (CPython View)

Every object has:

PyObject
 ├── ob_refcnt   (reference count)
 ├── ob_type     (pointer to type)
 └── data        (value / structure)

This is why:

• Assignment is cheap
• Passing objects is fast
• Mutation affects all references

4️⃣ Built-in Types: High-Level Taxonomy

Scalar (Immutable)

• int
• float
• bool
• complex
• NoneType

Sequence

• Immutable: str, tuple, bytes
• Mutable: list, bytearray

Set

• set (mutable)
• frozenset (immutable)

Mapping

• dict

Callable

• function
• method
• class

5️⃣ Singleton Objects (VERY IMPORTANT)

Some objects exist only once in the entire runtime.

Core singletons:

• None
• True
• False
• Ellipsis

a = None
b = None
a is b  # True

⚠️ You should always compare with is for None.

6️⃣ Truthiness Rules (Deep, Not Memorized)

Python does not have “true/false values”.
It has truthiness evaluation.

How Python decides truth:

1. If object defines __bool__() → use it
2. Else if defines __len__() → len != 0 is True
3. Else → True by default

Falsy objects:

False
None
0, 0.0, 0j
"", [], {}, set()

Interview trap:

class A:
    pass

bool(A())  # True

Why?

• No __bool__
• No __len__
• Default = True

7️⃣ bool Is a Subclass of int (Classic Trap)

issubclass(bool, int)  # True

True + True   # 2
False + True  # 1

This is intentional, not a bug.

8️⃣ None Is NOT 0, False, or Empty

None == False   # False
None == 0       # False
None == ""      # False

But:

if None:
    print("won't run")

Why?

• None is falsy
• But semantically distinct

🧠 Falsy ≠ False

9️⃣ is vs == (Now at System Level)

• == → value equality (__eq__)
• is → memory identity

a = []
b = []

a == b  # True
a is b  # False

Never confuse:

• Logical equality
• Physical identity

10️⃣ Dynamic Typing ≠ Weak Typing

Python is:

• ✅ Dynamically typed
• ✅ Strongly typed

1 + "1"   # TypeError

Type checks happen at runtime, not compile time.

11️⃣ How type() Actually Works

class A:
    pass

A = type("A", (), {})

This proves:

• Classes are created by calling type
• class is syntax sugar

This insight unlocks metaclasses (later days).

🔥 INTERVIEW TRAPS (DAY 5)

Q1

print(type(None))

✔ <class 'NoneType'>

Q2

print(type(object))

✔ <class 'type'>

Q3

print(type(type))

✔ <class 'type'>

Q4

print(bool([]) == False)

✔ True
But [] is False → False

🧠 DAY 5 MENTAL MODEL

Before asking “what does this do?”, ask:

1. Is it an object?
2. What is its type?
3. Does it define special methods?
4. Is identity or equality involved?

📝 DAY 5 ASSIGNMENT (MANDATORY)

1️⃣ Predict output (no running):

x = []
print(type(x) is list)
print(type(x) == list)

2️⃣ Explain clearly:

• Why Python doesn’t have primitives
• Why bool inherits from int

3️⃣ Whiteboard challenge:

Draw:

object
  ↑
 type
  ↑
 int

Explain this relationship verbally (interview-style).

🔜 DAY 6 PREVIEW

DAY 6 — Integers & Floats (CPython Internal Implementation)

You’ll learn:

• Why 10**1000 works
• Arbitrary precision integers
• Float precision limits
• Why 0.1 + 0.2 != 0.3

When ready, say 👉 “START DAY 6”