<s>[INST] can you write code? [/INST] Yes, I can write code. What programming language or task do you need help with?</s>\ <s>[INST] I need help to write a function that works as a sudoku filler , my problem is I get a lot of cells with the value of undefined [/INST] Sure! I can help you with that.

Here's a Python function that can fill in a Sudoku puzzle with missing values:

```python
def fill_sudoku(puzzle):
    """
    Fill in a Sudoku puzzle with missing values.

    Parameters:
    puzzle (list of lists): a 9x9 list of integers, where 0 represents a missing value

    Returns:
    A solved Sudoku puzzle as a list of lists
    """
    # Define a helper function to check if a value is valid in a given position
    def is_valid(row, col, value):
        # Check if the value is valid in the row
        if value in puzzle[row]:
            return False

        # Check if the value is valid in the column
        if value in [puzzle[i][col] for i in range(9)]:
            return False

        # Check if the value is valid in the 3x3 sub-grid
        subgrid_row, subgrid_col = (row // 3) * 3, (col // 3) * 3
        for i in range(subgrid_row, subgrid_row + 3):
            for j in range(subgrid_col, subgrid_col + 3):
                if puzzle[i][j] == value:
                    return False

        # If the value is valid in all three checks, return True
        return True

    # Define a helper function to solve the puzzle recursively
    def solve():
        # Find the first empty cell in the puzzle
        for row in range(9):
            for col in range(9):
                if puzzle[row][col] == 0:
                    # Try each possible value in the cell
                    for value in range(1, 10):
                        if is_valid(row, col, value):
                            # Set the cell to the valid value and try to solve the rest of the puzzle
                            puzzle[row][col] = value
                            if solve():
                                return True
                            # If the rest of the puzzle cannot be solved with this value, backtrack
                            puzzle[row][col] = 0
                    # If no valid value is found, return False
                    return False
        # If there are no empty cells, the puzzle is solved
        return True

    # Call the solve function to fill in the puzzle
    solve()

    # Return the solved puzzle
    return puzzle
```

You can call this function with a 9x9 list of integers where 0 represents a missing value, and it will return a solved Sudoku puzzle. If the puzzle is not solvable, the function will return the input puzzle unchanged.

Here's an example usage:

```python
board = [
    [5, 3, 0, 0, 7, 0, 0, 0, 0],
    [6, 0, 0, 1, 9, 5, 0, 0, 0],
    [0, 9, 8, 0, 0, 0, 0, 6, 0],
    [8, 0, 0, 0, 6, 0, 0, 0, 3],
    [4, 0, 0, 8, 0, 3, 0, 0, 1],
    [7, 0, 0, 0, 2, 0, 0, 0, 6],
    [0, 6, 0, 0, 0, 0, 2, 8, 0],
    [0, 0, 0, 4, 1, 9, 0, 0, 5],
    [0, 0, 0, 0, 8, 0, 0, 7, 9]
]

# fill the undefined cells
fill_sudoku(board)
```</s>