How to find and fix memory leaks in Python web applications?

We recently noticed that our FastAPI application running on Gunicorn workers keeps consuming memory until the OS kills the process. Restarting workers periodically hides the problem, but it is not a real solution. What tools and techniques work best for diagnosing memory leaks in long-running Python applications?

Using tracemalloc for Memory Audits

Python includes the tracemalloc module to take snapshots of allocated memory blocks.

import tracemalloc

# Start tracking memory allocations
tracemalloc.start()

# Take initial memory snapshot
snapshot1 = tracemalloc.take_snapshot()

# Perform suspect operation
# ... application workload here ...

# Take second snapshot to compare
snapshot2 = tracemalloc.take_snapshot()
top_stats = snapshot2.compare_to(snapshot1, 'lineno')

# Print top memory diffs
for stat in top_stats[:5]:
    print(stat)

Common Causes

• Global caches growing indefinitely without TTL
• Unclosed file descriptors or database sessions
• Circular references preventing garbage collection