Update Code Safely¶

Time: 10 minutes | Tools: update_symbol, rename_symbol | Tier: Community

Learn how to modify code safely with automatic backups and tracking.

What You'll Learn¶

• Replace functions/classes safely
• Rename symbols across files
• Automatic backup creation
• When updates fail and why

Prerequisites¶

• Completed Extract a Function
• Sample calculator.py file

The Problem with Manual Edits¶

When AI assistants edit code manually:

• Line numbers can be wrong
• Context may have changed
• Surrounding code might break
• No backup if something goes wrong

The Solution: Safe Symbol Updates¶

Code Scalpel's update_symbol:

1. Finds the symbol by name (not line numbers)
2. Creates a backup automatically
3. Replaces only that symbol
4. Preserves surrounding code

Step 1: Update a Function¶

Let's fix the divide function to handle zero:

"Update the divide function to check for division by zero"

The AI:

1. Extracts current code:

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

2. Creates improved version:

   def divide(a, b):
       """Divide a by b.
   
       Raises:
           ValueError: If b is zero.
       """
       if b == 0:
           raise ValueError("Cannot divide by zero")
       return a / b
   

3. Applies the update:

   {
     "tool": "update_symbol",
     "parameters": {
       "file_path": "calculator.py",
       "target_type": "function",
       "target_name": "divide",
       "new_code": "def divide(a, b):\n    \"\"\"Divide a by b.\n    \n    Raises:\n        ValueError: If b is zero.\n    \"\"\"\n    if b == 0:\n        raise ValueError(\"Cannot divide by zero\")\n    return a / b"
     }
   }
   

Response¶

{
  "data": {
    "file_path": "calculator.py",
    "target_name": "divide",
    "status": "updated",
    "backup_path": "calculator.py.bak",
    "lines_changed": {
      "before": [7, 9],
      "after": [7, 14]
    }
  },
  "tier_applied": "community",
  "duration_ms": 35
}

Step 2: Verify the Update¶

Check the file to see the change:

# calculator.py (after update)

def add(a, b):
    """Add two numbers."""
    return a + b

def divide(a, b):
    """Divide a by b.

    Raises:
        ValueError: If b is zero.
    """
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

# ... rest of file unchanged

Notice:

• Only divide changed
• add function untouched
• Calculator class untouched
• Formatting preserved

Step 3: Rename a Symbol¶

Now let's rename compute to calculate:

"Rename the compute method to calculate"

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

Response¶

{
  "data": {
    "old_name": "compute",
    "new_name": "calculate",
    "file_path": "calculator.py",
    "status": "renamed",
    "usages_updated": 1,
    "backup_path": "calculator.py.bak"
  },
  "tier_applied": "community",
  "duration_ms": 28
}

About Backups¶

Every update creates a backup:

To disable backups (not recommended):

{
  "tool": "update_symbol",
  "parameters": {
    "file_path": "calculator.py",
    "target_type": "function",
    "target_name": "divide",
    "new_code": "...",
    "create_backup": false
  }
}

When Updates Fail¶

Symbol Not Found¶

{
  "error": {
    "code": "SYMBOL_NOT_FOUND",
    "message": "Function 'divde' not found in calculator.py",
    "suggestions": ["divide"]
  }
}

Code Scalpel suggests corrections for typos!

Syntax Error in New Code¶

{
  "error": {
    "code": "SYNTAX_ERROR",
    "message": "Invalid Python syntax in new_code",
    "line": 3,
    "details": "expected ':'"
  }
}

The update is rejected—original file untouched.

File Not Found¶

{
  "error": {
    "code": "FILE_NOT_FOUND",
    "message": "File 'calculater.py' not found",
    "suggestions": ["calculator.py"]
  }
}

Update vs Rename¶

Try It Yourself¶

Exercise 1: Add Error Handling¶

"Update the add function to validate that inputs are numbers"

Exercise 2: Rename a Class¶

"Rename the Calculator class to MathCalculator"

Exercise 3: Update a Class¶

"Update the Calculator class to track operation counts"

Key Takeaways¶

1. update_symbol replaces code safely by name
2. rename_symbol renames and tracks usages
3. Backups are created automatically
4. Syntax errors are caught before writing
5. Typos are corrected with suggestions

Next Tutorial¶

Now that you can update code, learn to find security issues:

Run a Security Scan →