chore: add blog entry

Author: BlackDark

content/blog/2025-06-11-python-large-json.md

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+---
+title: "Efficiently Processing Large JSON Files in Python Without Loading Everything Into Memory"
+date: 2025-06-11T12:00:00+01:00
+draft: false
+language: en
+summary: Learn how to process large JSON datasets efficiently in Python using streaming and minimal memory, with practical code and profiling tips.
+description: A practical guide to efficiently processing large JSON files in Python without loading the entire file into memory. Covers streaming with ijson, memory profiling, and best practices for handling big data.
+author: raydak
+tags: [
+    "Python",
+    "JSON",
+    "Big Data",
+    "Streaming",
+    "ijson",
+    "memory-profiler"
+]
+categories: [
+    "Development",
+    "Data Processing"
+]
+---
+
+## Introduction
+
+Processing large JSON files can quickly exhaust your system's memory if you try to load the entire file at once. This is a common challenge in data engineering, ETL, and analytics workflows. Fortunately, Python offers tools to process such files efficiently by streaming the data and only keeping what's necessary in memory.
+
+This post demonstrates how to use [`ijson`](https://pypi.org/project/ijson/) for streaming JSON parsing and [`memory-profiler`](https://pypi.org/project/memory-profiler/) to monitor memory usage. We'll also show how to set up your environment with [`uv`](https://github.com/astral-sh/uv) for reproducible installs.
+
+## Why Not Just Use `json.load()`?
+
+The standard `json` module's `json.load()` reads the entire file into memory. For files larger than your available RAM, this leads to crashes or severe slowdowns. Instead, streaming parsers like `ijson` process the file incrementally.
+
+## Setting Up Your Environment
+
+First, initialize your Python project with `uv` and add the required dependencies:
+
+```sh
+uv init
+uv pip install ijson memory-profiler
+```
+
+## Streaming JSON Processing Example
+
+Suppose you have a large JSON array of objects and want to filter items matching a specific field (e.g., `"vpn": "ABC"`), writing only those to an output file. Here's how you can do it efficiently:
+
+```python
+from memory_profiler import profile
+import json
+import ijson
+import time
+
+backend = ijson  # You can also use ijson.get_backend("yajl2_c") for speed
+
+objects_num = 0
+
+# References:
+# https://pythonspeed.com/articles/json-memory-streaming/
+# https://www.dataquest.io/blog/python-json-tutorial/
+# https://pytutorial.com/python-json-streaming-handle-large-datasets-efficiently/
+# https://github.com/kashifrazzaqui/json-streamer
+
+@profile
+def filter_large_json(input_file, output_file, target_vpn):
+    global objects_num
+    with open(input_file, "rb") as infile, open(output_file, "w") as outfile:
+        outfile.write("[")
+        first = True
+        for obj in backend.items(infile, "item"):
+            if obj.get("vpn") == target_vpn:
+                if not first:
+                    outfile.write(",")
+                json.dump(obj, outfile)
+                first = False
+                objects_num += 1
+        outfile.write("]")
+    print(f"Filtered {objects_num} objects with vpn '{target_vpn}'.")
+
+start_time = time.time()
+filter_large_json("test.json", "output.json", "ABC")
+print("--- %s seconds ---" % (time.time() - start_time))
+```
+
+## Profiling Memory Usage
+
+The `@profile` decorator from `memory-profiler` will show you the memory usage line by line when you run your script with:
+
+```sh
+mprof run your_script.py
+mprof plot
+```
+
+## Conclusion
+
+By streaming your JSON processing, you can handle files of virtually any size, limited only by disk space, not RAM. This approach is essential for scalable data pipelines and analytics.
+
+## References
+
+- [Streaming large JSON files in Python](https://pythonspeed.com/articles/json-memory-streaming/)
+- [Python JSON streaming: handle large datasets efficiently](https://pytutorial.com/python-json-streaming-handle-large-datasets-efficiently/)
+- [Dataquest: Working with JSON in Python](https://www.dataquest.io/blog/python-json-tutorial/)
+- [json-streamer GitHub](https://github.com/kashifrazzaqui/json-streamer)