Use pprint for Nested Structure Debug Output in Python

Pretty-print nested dictionaries and lists with pprint for readable, organized debug output.

Easy Python 3.9+ Aug 9, 2026 Errors & debugging 15 views 0 copies

pprint debugging nested-structure output

Python code

25 lines

Python 3.9+

from pprint import pprint

def build_nested_structure():
    """Create a sample nested data structure for demonstration."""
    return {
        "project": "DataPipeline",
        "config": {
            "inputs": ["raw_1.json", "raw_2.json"],
            "processing": {
                "steps": ["clean", "transform", "validate"],
                "parameters": {
                    "clean": {"strategy": "remove_empty", "min_len": 3},
                    "transform": {"decimal_places": 2},
                    "validate": {"schema_version": "2.1.0", "strict": True}
                }
            }
        },
        "output": {"format": "parquet", "compression": "snappy"}
    }


if __name__ == "__main__":
    data = build_nested_structure()
    print("Pretty-printed nested structure:")
    pprint(data, indent=2, width=50, sort_dicts=True)

Output

stdout

Pretty-printed nested structure:
{ 'config': { 'inputs': ['raw_1.json',
                        'raw_2.json'],
               'processing': { 'parameters': { 'clean': { 'min_len': 3,
                                                          'strategy': 'remove_empty'},
                                                 'transform': { 'decimal_places': 2},
                                                 'validate': { 'schema_version': '2.1.0',
                                                               'strict': True}},
                                'steps': ['clean', 'transform', 'validate']}},
  'output': {'compression': 'snappy', 'format': 'parquet'},
  'project': 'DataPipeline'}

How it works

The pprint module formats nested data structures with indentation, line wrapping, and sorted keys (when sort_dicts=True), making complex output much easier to scan. Parameters like indent and width control the layout: indent sets the nested indentation level, while width caps line length causing long lists and dictionaries to break cleanly across lines. pprint recursively walks the structure, so deeply nested dictionaries and lists are handled consistently. This makes it ideal for debugging logs and inspecting API responses where you need to see the full shape of the data.

Common mistakes

Using `print()` on a nested dict, which outputs a single unreadable line
Forgetting `sort_dicts=True` when you want deterministic key order across runs
Setting `width` too high, so long values still overflow and defeat the purpose
Applying `pprint.pp()` without arguments and wondering why layout looks different than expected

Variations

Use `pprint.pp(data, indent=4, width=100)` for tighter or wider output
Use `pprint.pformat(data)` to capture the formatted string and reuse it in logs

Real-world use cases

Debugging a JSON response from an API, showing nested fields and lists clearly during development.
Inspecting configuration dictionaries loaded from YAML files to verify structure before processing.
Logging complex state of a data pipeline job to trace issues in transformation steps.

Use pprint for Nested Structure Debug Output in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Real-world use cases

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