JSON File

JSON Handling Specifications

Goals

• Safely parse JSON/JSONL without memory overflow.
• Discover schema structure (keys, nesting depth, data types).
• Flatten complex nested structures into tabular data when necessary.
• Handle inconsistent schemas and "dirty" JSON (e.g., trailing commas, mixed types).

Inspection (Always First)

• Structure Discovery:
  • Determine if the root is a list or a dict.
  • Identify if it's a standard JSON or JSONL (one valid JSON object per line).
• Schema Sampling:
  • For large files, read the first few objects/lines to infer the schema.
  • Identify top-level keys and their types.
  • Detect nesting depth: If depth > 3, consider it a "deeply nested" structure.
• Size Check:
  • If the file is large (>50MB), avoid json.load(). Use iterative parsing or streaming.

Processing & Extraction

• Lazy Loading (Streaming):
  • For massive JSON: Use ijson (Python) or similar streaming parsers to yield specific paths/items.
  • For JSONL: Read line-by-line using a generator to minimize memory footprint.
• Flattening & Normalization:
  • Use pandas.json_normalize to convert nested structures into flat tables if the goal is analysis.
  • Specify max_level during normalization to prevent "column explosion."
• Data Filtering:
  • Extract only required sub-trees (keys) early in the process to reduce the memory object size.

Data Quality & Schema Validation

• Missing Keys: Use .get(key, default) or try-except blocks. Never assume a key exists in all objects.
• Type Coercion:
  • Validate numeric strings vs. actual numbers.
  • Standardize null, "", and [] consistently.
• Encoding: Default to UTF-8; check for BOM (utf-8-sig) if parsing fails.
• Malformed JSON Recovery:
  • For minor syntax errors (e.g., single quotes instead of double), attempt ast.literal_eval or regex-based cleanup only as a fallback.

Best Practices

• Minimal Reads: Don't load a 50MB JSON just to read one config key; use a streaming approach.
• Schema Logging: Document the detected structure (e.g., "Root is a list of 500 objects; key 'metadata' is nested").
• Error Transparency: When a JSON object in a JSONL stream is corrupted, log the line number, skip it, and continue instead of crashing the entire process.
• Avoid Over-Flattening: Be cautious with deeply nested arrays; flattening them can lead to massive row duplication.
• Strict Typing: After extraction, explicitly convert types (e.g., pd.to_datetime) to ensure downstream reliability.

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