Extract a Function¶

Time: 5 minutes | Tools: extract_code | Tier: Community

Learn how to surgically extract functions by name—no line number guessing.

What You'll Learn¶

• How extract_code finds code by name
• Extracting functions, classes, and methods
• Including dependencies automatically

Prerequisites¶

• Completed Analyze Your First File
• Sample code from previous tutorial

The Problem with Line Numbers¶

Traditional approach (fragile):

"Read lines 7-9 of calculator.py"

This breaks if:

• Someone adds a comment above line 7
• The file is reformatted
• Imports are added at the top

The Solution: Extract by Name¶

With Code Scalpel:

"Extract the divide function from calculator.py"

The AI calls:

{
  "tool": "extract_code",
  "parameters": {
    "file_path": "calculator.py",
    "target_type": "function",
    "target_name": "divide"
  }
}

Step 1: Extract a Function¶

Ask your AI:

"Show me the divide function from calculator.py"

Response¶

{
  "data": {
    "target_type": "function",
    "target_name": "divide",
    "code": "def divide(a, b):\n    \"\"\"Divide a by b.\"\"\"\n    return a / b",
    "line_start": 7,
    "line_end": 9,
    "dependencies": [],
    "token_estimate": 25
  },
  "tier_applied": "community",
  "duration_ms": 18
}

Notice:

• Exact code extracted
• Line numbers provided (but you didn't need them)
• Dependencies listed
• Token cost estimated

Step 2: Extract a Class¶

Try extracting the Calculator class:

"Extract the Calculator class from calculator.py"

{
  "tool": "extract_code",
  "parameters": {
    "file_path": "calculator.py",
    "target_type": "class",
    "target_name": "Calculator"
  }
}

Response¶

{
  "data": {
    "target_type": "class",
    "target_name": "Calculator",
    "code": "class Calculator:\n    \"\"\"Simple calculator class.\"\"\"\n    \n    def __init__(self):\n        self.history = []\n    \n    def compute(self, operation, *args):\n        \"\"\"Perform a calculation.\"\"\"\n        result = add(*args) if operation == \"add\" else divide(*args)\n        self.history.append(result)\n        return result",
    "line_start": 11,
    "line_end": 21,
    "dependencies": ["add", "divide"],
    "token_estimate": 85
  }
}

Note the dependencies field shows this class uses add and divide.

Step 3: Extract a Method¶

Extract a specific method from a class:

"Extract the compute method from the Calculator class"

{
  "tool": "extract_code",
  "parameters": {
    "file_path": "calculator.py",
    "target_type": "method",
    "target_name": "Calculator.compute"
  }
}

Step 4: Include Context¶

If you need the dependencies too:

"Extract the Calculator class with all its dependencies"

{
  "tool": "extract_code",
  "parameters": {
    "file_path": "calculator.py",
    "target_type": "class",
    "target_name": "Calculator",
    "include_context": true
  }
}

This includes the add and divide functions along with the class.

Target Types¶

Why This Matters¶

Token Efficiency¶

Instead of sending 1000 lines to the AI, extract just what's needed:

Precision¶

The AI works with exactly the code it needs—no confusion from unrelated code.

Reliability¶

Extraction by name works even when:

• Files are reformatted
• Comments are added
• Code is moved around

Try It Yourself¶

Exercise 1: Your Own Code¶

Extract a function from your own project:

"Extract the [function_name] function from [your_file.py]"

Exercise 2: React Components¶

If you have React code:

"Extract the Button component from Button.tsx"

Code Scalpel supports JSX and TSX.

Exercise 3: Check Dependencies¶

"Extract [function] and show what it depends on"

See what other code your function needs.

Common Errors¶

"Symbol not found"

The function name doesn't exist. Check spelling or use analyze_code first.

"File not found"

The file path is wrong. Use validate_paths to check.

Key Takeaways¶

1. extract_code finds code by name, not line numbers
2. It automatically identifies dependencies
3. Token-efficient: only get what you need
4. Works with functions, classes, and methods
5. Supports Python, JS, TS, Java, JSX, TSX

Next Tutorial¶

Now that you can extract code, learn to update it safely:

Update Code Safely →