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Solved : Python ResourceWarning: unclosed <socket.socket>

4 min readMar 19, 2025
Networking and Python

Every time a financial transaction is processed in a high-frequency trading system, multiple connections are opened and closed within milliseconds. These systems rely on efficient socket communication to maintain real-time data feeds and execute orders. But what happens when sockets aren’t closed properly? Resources are left hanging, leading to unexpected behaviors, degraded performance, and even system failures. A ResourceWarning: unclosed <socket.socket> in Python is a subtle but critical sign that a network resource was not properly cleaned up. In environments where reliability is non-negotiable, such issues can lead to catastrophic consequences.

When Python Sockets Go Rogue

Python provides an easy way to create and manage sockets using the socket module. However, a common oversight is neglecting to close sockets explicitly, leading to resource leaks. When a socket is opened, it occupies a file descriptor, a finite resource in any operating system. If too many sockets remain unclosed, the system eventually exhausts available descriptors, leading to failures in new network connections. This issue typically manifests in long-running applications, microservices handling high request loads, or scripts that create multiple connections without proper cleanup.

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Johan Louwers
Johan Louwers

Written by Johan Louwers

Johan Louwers is a technology enthousiasts with a long background in supporting enterprises and startups alike as CTO, Chief Enterprise Architect and developer.

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