How to use the xlwings.Book.caller function in xlwings

def combobox():
    """
    This populates the ComboBox with the values from the database
    """

    # Make a connection to the calling Excel file
    wb = Book.caller()

    # Place the database next to the Excel file
    db_file = os.path.join(os.path.dirname(wb.fullname), 'chinook.sqlite')

    # Database connection and creation of cursor
    con = sqlite3.connect(db_file, detect_types=sqlite3.PARSE_DECLTYPES | sqlite3.PARSE_COLNAMES)
    cursor = con.cursor()

    # Database Query
    cursor.execute("SELECT PlaylistId, Name FROM Playlist")

    # Write IDs and Names to hidden sheet
    Range('Source', 'A1').table.clear_contents()
    Range('Source', 'A1').value = cursor.fetchall()

    # Format and fill the ComboBox to show Names (Text) and give back IDs (Values)

def _make_connections():
    global wb, sht, directory
    wb = xw.Book.caller()
    sht = wb.sheets.active
    directory = os.path.dirname(wb.fullname)

def playlist():
    """
    Get the playlist content based on the ID from the Dropdown
    """
    # Make a connection to the calling Excel file
    wb = Book.caller()

    # Place the database next to the Excel file
    db_file = os.path.join(os.path.dirname(wb.fullname), 'chinook.sqlite')

    # Database connection and creation of cursor
    con = sqlite3.connect(db_file, detect_types=sqlite3.PARSE_DECLTYPES | sqlite3.PARSE_COLNAMES)
    cursor = con.cursor()

    # Get PlaylistId from ComboBox
    playlist_id = wb.xl_workbook.ActiveSheet.OLEObjects("ComboBox1").Object.Value

    # Database query
    cursor.execute(
        """
        SELECT
        t.Name AS Track, alb.Title AS Album,  art.Name AS Artist, t.Composer

def get_harvest_time_entries():
    wb = xw.Book.caller()

    sheets = xw.sheets

    time_entries_sheet = None
    for sheet in sheets:
        if sheet.name == 'Harvest Time Entries':
            time_entries_sheet = sheet

    if time_entries_sheet is not None:
        time_entries_sheet.delete()

    new_time_entries = sheets.add(name='Harvest Time Entries', after='Sheet1')

    wb.app.screen_updating = False
    wb.app.calculation = 'manual'

def main():
    # Create a reference to the calling Excel Workbook
    wb = xw.Book.caller()

    # Get the constant from Excel
    const = xw.Range('B1').value

    # Get the figure and show it in Excel
    fig = get_figure(const)
    plot = xw.Plot(fig)
    plot.show('MyStreamplot', sheet=1)

def make_employee_pivot_table():
    # get the worksheet we are interested in (providing it exists)
    wb = xw.Book.caller()
    sheets = xw.sheets
    working_sheet = None
    for sheet in sheets:
        if sheet.name == 'Employee Hours':
            working_sheet = sheet

    for col in range(1, working_sheet.used_range.columns.count + 1):
        if working_sheet.cells(1, col).value == 'Project Code':
            code_position = col

        if working_sheet.cells(1, col).value == 'Last Name':
            surname_position = col

        if working_sheet.cells(1, col).value == 'total':
            total_position = col

def employee_rate_and_total(sheet_range = 'Employee Hours', sheet_lookup = 'Employee Rates'):

    # get the worksheet we are interested in (providing it exists)
    wb = xw.Book.caller()
    sheets = xw.sheets
    working_sheet = None
    for sheet in sheets:
        if sheet.name == sheet_range:
            working_sheet = sheet

    if working_sheet is not None:
        Lookup_cols = working_sheet.used_range.columns.count
        Lookup_rows = working_sheet.used_range.rows.count + 1

        rates_col = Lookup_cols + 1                   #calculates the column number for the rates
        total_col = Lookup_cols + 2                    #calculates the row number for the rates
        rows = working_sheet.used_range.rows.count             #calculates the number of rows in "Sheet1"
        code_position = 0
        surname_position = 0
        hours_position = 0

def refresh():
    """
    Refreshes the tables in Excel given the input parameters.
    """
    # Connect to the Workbook
    wb = Book.caller()

    # Read input
    start_date = Range(sheet_dashboard, 'start_date').value
    end_date = Range(sheet_dashboard, 'end_date').value
    account_name = Range(sheet_dashboard, 'account').value
    property_name = Range(sheet_dashboard, 'property').value
    profile_name = Range(sheet_dashboard, 'view').value
    max_results = Range(sheet_dashboard, 'max_rows').value

    # Clear Content
    Range(sheet_dashboard, 'behavior').clear_contents()
    Range(sheet_dashboard, 'effective').clear_contents()

    # Behavior table
    behavior(start_date, end_date, account_name, property_name, profile_name, max_results)

def get_harvest_invoices():
    wb = xw.Book.caller()

    sheets = xw.sheets

    invoice_sheet = None
    for sheet in sheets:
        if sheet.name == 'Harvest Invoices':
            invoice_sheet = sheet

    if invoice_sheet is not None:
        invoice_sheet.delete()

    new_invoices = sheets.add(name='Harvest Invoices', after='Sheet1')

    wb.app.screen_updating = False
    wb.app.calculation = 'manual'