字符串格式为空字符串导致打印中有多余空间

我想字符串格式的句子如下:

integer = 1
if integer != 1:
    n_val, book = integer, 'books'
else:
    n_val, book ='', 'book'

print(f'Fetch the top {n_val} children {book}.')

我希望看到:

Fetch the top 3 children books.

或

Fetch the top children book.

如果integer不为1,则它有效,但是,当 integer =1 ,字符串格式在integer的位置给了我一个额外的空间,如下所示:

Fetch the top  children book.

当 整数=1 ?