# Connect to a Book¶

When reading/writing data to the active sheet, you don’t need a book object:

>>> import xlwings as xw
>>> xw.Range('A1').value = 'something'


## Python to Excel¶

The easiest way to connect to a book is offered by xw.Book: it looks for the book in all app instances and returns an error, should the same book be open in multiple instances. To connect to a book in the active app instance, use xw.books and to refer to a specific app, use:

>>> app = xw.App()  # or something like xw.apps[10559] for existing apps, get the available PIDs via xw.apps.keys()
>>> app.books['Book1']

xw.Book xw.books
New book xw.Book() xw.books.add()
Unsaved book xw.Book('Book1') xw.books['Book1']
Book by (full)name xw.Book(r'C:/path/to/file.xlsx') xw.books.open(r'C:/path/to/file.xlsx')

Note

When specifying file paths on Windows, you should either use raw strings by putting an r in front of the string or use double back-slashes like so: C:\\path\\to\\file.xlsx.

## Excel to Python (RunPython)¶

To reference the calling book when using RunPython in VBA, use xw.Book.caller(), see Call Python with “RunPython”. Check out the section about Debugging to see how you can call a script from both sides, Python and Excel, without the need to constantly change between xw.Book.caller() and one of the methods explained above.

## User Defined Functions (UDFs)¶

Unlike RunPython, UDFs don’t need a call to xw.Book.caller(), see VBA: User Defined Functions (UDFs). However, it’s available (restricted to read-only though), which sometimes proofs to be useful.