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[Tut] Python __sizeof__() Method

Python __sizeof__() Method

Syntax

``object.__sizeof__(self, other)``

The Python `__sizeof__()` method returns the size of the object in bytes. The `sys.getsizeof()` method internally call’s `__sizeof__()` and adds some additional byte overhead, e.g., for garbage collection.

Basic Example

The following code snippet creates a list object `x` with three integers and measures its size in bytes (104) using the `x.__sizeof__()` method call.

It then measures the size with overhead using `sys.getsizeof(x)`.

```>>> import sys
>>> x = [1, 2, 3]
>>> x.__sizeof__()
104
>>> sys.getsizeof(x)
120```

Let’s make the list much larger to measure if it has any impact on the size in bytes.

```>>> import sys
>>> x = list(range(10000))
>>> x.__sizeof__()
80040
>>> sys.getsizeof(x)
80056```

This list is built using the `range()` function. It has 10000 integers, each needing 8 bytes with a constant overhead of 40 bytes for the list structure, the `x.__sizeof__()` method call results in 10000 * 8 + 40 = 80040 bytes.

You can see that in both cases, the `sys.getsizeof(x)` has 16 more bytes than `x.__sizeof__()` which seems to be the overhead on my particular machine for this particular example.

Overriding __sizeof__()

You can override the `__sizeof__()` method for your own custom data type by defining the `__sizeof__()` method with one argument `self` (that is passed automatically by Python).

```import sys class Data: def __sizeof__(self): return 42 x = Data()
print(x.__sizeof__()) ```

The `__sizeof__()` method returns the integer 42 that was returned by us—not the number of bytes.

Let’s call the `sys.getsizeof()` method to see if the difference is 16 bytes for the GC overhead!

```import sys class Data: def __sizeof__(self): return 42 x = Data() print(x.__sizeof__())
# 42 print(sys.getsizeof(x))
# 58```

References:

Where to Go From Here?

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https://www.sickgaming.net/blog/2021/12/...__-method/

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