# JSON to CSV Converter

This utility converts a JSON file (specifically a list of objects) into a CSV file. It automatically detects all unique keys across the JSON objects to create the CSV headers, ensuring no data is lost even if some objects have missing fields.

**Modules Used:**
*   [[programming/python/modules/json-module|json]]: To parse the input JSON file.
*   [[programming/python/modules/csv-module|csv]]: To write the output CSV file.
*   [[programming/python/modules/argparse-module|argparse]]: To handle command-line arguments.

## The Code

Save this as `json2csv.py`.

```python
import json
import csv
import argparse
import sys

def convert_json_to_csv(json_file, csv_file):
    try:
        # 1. Load JSON Data
        with open(json_file, 'r', encoding='utf-8') as jf:
            data = json.load(jf)
        
        # Validate structure: Expecting a list of dictionaries
        if not isinstance(data, list):
            print("Error: JSON root must be a list of objects (e.g., [{}, {}]).")
            return
        
        if not data:
            print("Error: JSON file is empty.")
            return

        # 2. Determine Headers
        # Collect all unique keys from all objects to handle inconsistent schemas
        headers = set()
        for entry in data:
            if isinstance(entry, dict):
                headers.update(entry.keys())
        
        # Sort headers for consistent output
        fieldnames = sorted(list(headers))

        # 3. Write CSV
        with open(csv_file, 'w', newline='', encoding='utf-8') as cf:
            writer = csv.DictWriter(cf, fieldnames=fieldnames)
            
            writer.writeheader()
            
            # writerows automatically handles missing keys by leaving cells empty
            writer.writerows(data)
            
        print(f"Successfully converted '{json_file}' to '{csv_file}'")
        print(f"Processed {len(data)} records.")

    except FileNotFoundError:
        print(f"Error: File '{json_file}' not found.")
    except json.JSONDecodeError:
        print(f"Error: Failed to decode JSON from '{json_file}'. Check syntax.")
    except Exception as e:
        print(f"An error occurred: {e}")

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="JSON to CSV Converter")
    parser.add_argument("input", help="Input JSON file path")
    parser.add_argument("output", help="Output CSV file path")
    
    args = parser.parse_args()
    
    convert_json_to_csv(args.input, args.output)
```

## Usage

```bash
python json2csv.py data.json output.csv
```

[[programming/python/python]]