Do you ever find yourself trying to figure out how large a specific Python object is in bytes? Whether you’re dealing with lists, dictionaries, strings, or objects, understanding the size of an object can be essential for building efficient code. In this blog post, we’ll dive into the steps needed to discover exactly what the size of a particular Python object is.

Let’s explore these tips right away!

To get the size of a Python object, you can use the sys.getsizeof() function. This function returns the size of an object in bytes.
Here is an example of how to use it:

				
					import sys

x = [1, 2, 3]
size = sys.getsizeof(x)
print(size)

This will print the size of the list x in bytes.

Keep in mind that the sys.getsizeof() function only returns the size of the object itself, and does not include the size of any objects it references. For example, if x is a list that contains references to other objects, sys.getsizeof(x) will only return the size of the list, not the size of the objects that the list references.

Additionally, the size returned by sys.getsizeof() may not be accurate for certain types of objects, such as objects that use dynamically-allocated memory or objects that override the __sizeof__() method.

Suppose you want to get a more accurate and comprehensive measurement of the size of an object and all of the objects it references. In that case, you may need to use a different approach, such as recursively traversing the object tree and adding up the sizes of each object.

How Does It Work?

The main issue with the sys.getsizeof() function is that it sometimes returns inaccurate results. This is because the size of an object can be affected by many factors, including the number of references to that object, its internal structure, and other variables.

As a result, the sys.getsizeof() function may overestimate the actual size of an object. Furthermore, the sys.getsizeof() function only returns an object’s direct memory usage and not that object’s total memory usage. This can create a situation where an object uses much more than its reported size, leading to higher memory utilization than expected.

Here is an example of how to use the sys.getsizeof() function to get the size of various types of objects in Python:

				
					import sys

# Get the size of a list
x = [1, 2, 3]
size = sys.getsizeof(x)
print(f"Size of list x: {size} bytes")

# Get the size of a tuple
y = (1, 2, 3)
size = sys.getsizeof(y)
print(f"Size of tuple y: {size} bytes")

# Get the size of a dictionary
z = {'a': 1, 'b': 2}
size = sys.getsizeof(z)
print(f"Size of dictionary z: {size} bytes")

# Get the size of a string
s = "hello"
size = sys.getsizeof(s)
print(f"Size of string s: {size} bytes")

# Get the size of an integer
i = 10
size = sys.getsizeof(i)
print(f"Size of integer i: {size} bytes")

This will output the following:

				
					Size of list x: 104 bytes
Size of tuple y: 72 bytes
Size of dictionary z: 280 bytes
Size of string s: 53 bytes
Size of integer i: 28 bytes

Remember that the size returned by sys.getsizeof() may not be accurate for certain types of objects, such as objects that use dynamically-allocated memory or objects that override the __sizeof__() method. Additionally, sys.getsizeof() only returns the size of the thing itself, and does not include the size of any objects it references.

How to Measure the True Size of a Python Object?

You can use the pympler library to measure the actual size of a Python object and all objects it references. pympler is a library that provides tools for analyzing the memory usage of Python programs.

To use the pympler to measure the size of a Python object, you can use the asizeof function from the pympler.asizeof module. This function returns the size of an object in bytes, including the size of all objects it references.

Here is an example of how to use the asizeof function to measure the size of a Python object:

				
					pip install pympler

With pympler installed, you can start estimating the size of your Python objects by using the pympler.asizeof.asizeof() function.

Example:

				
					from pympler import asizeof

x = [1, 2, 3]
size = asizeof.asizeof(x)
print(size)

This will print the size of the list x and all objects it references, in bytes.

You can also use the asizeof function to measure the size of specific types of objects, such as dictionaries or lists, using the flatten argument. For example:

				
					from pympler import asizeof

x = {'a': 1, 'b': 2}
size = asizeof.asizeof(x, flatten=True)
print(size)

This will print the size of the dictionary x, including the size of all objects it references, in bytes.

Remember that the asizeof function may not be accurate for particular objects, such as objects that use dynamically-allocated memory or objects that override the __sizeof__() method. Additionally, asizeof may not be able to measure the size of some objects, such as objects created by C extension modules.

Wrap up

There are several ways to measure the size of a Python object, including using the sys.getsizeof() function, using a recursive approach to traverse the object tree and add up the sizes of each object, or using the pympler library. The specific approach you choose will depend on your needs and the characteristics of the objects you are working with.

It’s important to remember that the size of an object may not be accurately measured by any of these approaches for certain types of objects, such as objects that use dynamically-allocated memory or objects that override the __sizeof__() method. Additionally, these approaches may only measure the size of the object itself and not the size of any objects it references.

To get a more accurate and comprehensive measurement of the size of an object and all objects it references, you may need to use a combination of different approaches or consider using a separate tool designed explicitly for measuring memory usage.


Thanks for reading. Happy coding!