Day 42:Not using __slots__ when needed

🐍 Python Mistakes Everyone Makes ❌

Day 42: Not Using __slots__ When Needed

Python classes are flexible by default—but that flexibility comes with a cost. When you create many objects, not using __slots__ can silently waste memory and reduce performance.

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❌ The Mistake

Defining classes without __slots__ when you know exactly which attributes the objects will have.

class Point:
   def __init__(self, x, y):
      self.x = x 

        self.y = y

This looks perfectly fine—but every instance gets a __dict__ to store attributes dynamically.

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❌ Why This Fails

• Each object stores attributes in a __dict__
  

• Extra memory overhead per instance

• Slower attribute access

• Allows accidental creation of new attributes

• Becomes expensive when creating thousands or millions of objects

This usually goes unnoticed until performance or memory becomes a problem.

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✅ The Correct Way

Use __slots__ when:

• Object structure is fixed

• You care about memory or speed

• You’re creating many instances

class Point:
    __slots__ = ("x", "y")

  def __init__(self, x, y):
        self.x = x 

        self.y = y

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✅ What __slots__ Gives You

• 🚀 Lower memory usage

• ⚡ Faster attribute access

• 🛑 Prevents accidental attributes

• 🧠 Clear object structure

p = Point(1, 2)

p.z = 3 # ❌ AttributeError

This is a feature, not a limitation.

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🧠 When NOT to Use __slots__

• When objects need dynamic attributes

• When subclassing extensively (needs extra care)

• When simplicity matters more than optimization

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🧠 Simple Rule to Remember

🐍 Many objects + fixed attributes → use __slots__
🐍 Few objects or flexible design → skip it

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🚀 Final Takeaway

__slots__ is not mandatory—but it’s powerful when used correctly.

Use it when:

• Performance matters

• Memory matters

• Object structure is predictable

Write Python that’s not just correct—but efficient too.