Day 35: Assuming __del__ Runs Immediately

 

🐍 Python Mistakes Everyone Makes ❌

Day 35: Assuming __del__ Runs Immediately

Python’s __del__ method looks like a destructor, so it’s easy to assume it behaves like one in languages such as C++ or Java.
But this assumption can lead to unpredictable bugs and resource leaks.

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❌ The Mistake

Relying on __del__ to clean up resources immediately when an object is “deleted”.

class Demo:
    def __del__(self):
        print("Object deleted")

obj = Demo()

obj = None # ❌ assuming __del__ runs here

You might expect "Object deleted" to print right away — but that is not guaranteed.

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❌ Why This Fails

• __del__ is called only when an object is garbage collected

• Garbage collection timing is not guaranteed

• Other references to the object may still exist

• Circular references can delay or prevent __del__

• Behavior can vary across Python implementations (CPython, PyPy, etc.)

In short:
👉 Deleting a reference ≠ deleting the object

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⚠️ Real-World Problems This Causes

• Files left open

• Database connections not closed

• Network sockets hanging

• Memory leaks

• Inconsistent behavior across environments

These bugs are often hard to detect and harder to debug.

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✅ The Correct Way

Always clean up resources explicitly.

class Resource:
   def close(self):
     print("Resource released")

r = Resource()
try:
   print("Using resource")
finally:

 r.close() # ✅ guaranteed cleanup

This ensures cleanup no matter what happens.

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🧠 Even Better: Use with

When possible, use context managers:

with open("data.txt") as f:
   data = f.read()

# file is safely closed here

Python guarantees cleanup when exiting the with block.

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🚫 Why __del__ Is Dangerous for Cleanup

• Order of destruction is unpredictable

• May never run before program exits

• Errors inside __del__ are ignored

• Makes code fragile and hard to reason about

__del__ is for last-resort cleanup, not critical resource management.

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🧠 Simple Rule to Remember

🐍 Never rely on __del__ for important cleanup
🐍 Use with or explicit cleanup methods instead

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🚀 Final Takeaway

If a resource must be released, don’t wait for Python to decide when.

Be explicit.
Be predictable.
Write safer Python.