Threading and Multiprocessing#

New in version 0.13.0.

Threading#

While xlwings is not technically thread safe, it’s still easy to use it in threads as long as you have at least v0.13.0 and stick to a simple rule: Do not pass xlwings objects to threads. This rule isn’t a requirement on macOS, but it’s still recommended if you want your programs to be cross-platform.

Consider the following example that will NOT work:

import threading
from queue import Queue
import xlwings as xw

num_threads = 4


def write_to_workbook():
    while True:
        myrange = q.get()
        myrange.value = myrange.address
        print(myrange.address)
        q.task_done()


q = Queue()

for i in range(num_threads):
    t = threading.Thread(target=write_to_workbook)
    t.daemon = True
    t.start()

for cell in ['A1', 'A2', 'A3', 'A4', 'A5', 'A6', 'A7', 'A8', 'A9', 'A10']:
    # THIS DOESN'T WORK - passing xlwings objects to threads will fail!
    myrange = xw.Book('Book1.xlsx').sheets[0].range(cell)
    q.put(myrange)

q.join()

To make it work, you simply have to fully qualify the cell reference in the thread instead of passing a Book object:

import threading
from queue import Queue
import xlwings as xw

num_threads = 4


def write_to_workbook():
    while True:
        cell_ = q.get()
        xw.Book('Book1.xlsx').sheets[0].range(cell_).value = cell_
        print(cell_)
        q.task_done()


q = Queue()

for i in range(num_threads):
    t = threading.Thread(target=write_to_workbook)
    t.daemon = True
    t.start()

for cell in ['A1', 'A2', 'A3', 'A4', 'A5', 'A6', 'A7', 'A8', 'A9', 'A10']:
    q.put(cell)

q.join()

Multiprocessing#

Note

Multiprocessing is only supported on Windows!

The same rules apply to multiprocessing as for threading, here’s a working example:

from multiprocessing import Pool
import xlwings as xw


def write_to_workbook(cell):
    xw.Book('Book1.xlsx').sheets[0].range(cell).value = cell
    print(cell)


if __name__ == '__main__':
    with Pool(4) as p:
        p.map(write_to_workbook,
              ['A1', 'A2', 'A3', 'A4', 'A5', 'A6', 'A7', 'A8', 'A9', 'A10'])