How to measure function memory with sys.getsizeof in Python

Measure the memory footprint of Python functions (user-defined and built-in) using sys.getsizeof.

Easy Python 3.9+ Aug 9, 2026 Functions & basics 13 views 0 copies

sys getsizeof memory functions measurement

Python code

13 lines

Python 3.9+

import sys

def sample_function(a, b, c):
    return a + b - c

def measure_function_memory(func):
    size = sys.getsizeof(func)
    print(f"Memory size of {func.__name__}: {size} bytes")

if __name__ == "__main__":
    measure_function_memory(sample_function)
    measure_function_memory(print)
    measure_function_memory(len)

Output

stdout

Memory size of sample_function: 144 bytes
Memory size of print: 72 bytes
Memory size of len: 72 bytes

How it works

sys.getsizeof returns the size of the object in bytes, including only the object itself, not referenced objects. For user-defined functions, the size includes the code object and metadata; built-ins like print and len are typically smaller. This is a diagnostic tool, not a precise memory profiler for the function's entire closure or referenced data.

Common mistakes

Assuming getsizeof includes referenced objects (it doesn't by default).
Measuring the function call result instead of the function object (e.g., `sys.getsizeof(func(...))`).
Comparing sizes across Python versions or interpreters, as they vary.

Variations

Use `sys.getsizeof(func, default=0)` to avoid TypeError for objects without size info.
Use `tracemalloc` for deeper memory analysis of function execution.

Real-world use cases

Debugging why a Python process uses more memory than expected by checking object sizes.
Estimating overhead when caching functions or storing them in data structures.
Profiling memory usage differences between built-in and custom functions in a performance audit.

How to measure function memory with sys.getsizeof in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Functions & basics

Tutorials

Quizzes

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Functions & basics

Keep learning

Tutorials

Quizzes