Python-docx: Changing line spacing for one table changes it in all tables

I am trying to change the line spacing of a table in an existing document but it changes the line spacing of all the tables in the document.

Here is a reproducible example, creating a document with three tables:

from docx import Document
from docx.shared import Inches
from docx.shared import Pt
from docx.enum.text import WD_LINE_SPACING

document = Document()

# Some sample text to add to tables
records = (
    (3, '101', 'Spam'),
    (7, '422', 'Eggs'),
    (4, '631', 'Spam, spam, eggs, and spam')
)

# Create table 0
table = document.add_table(rows=1, cols=3)
hdr_cells = table.rows[0].cells
hdr_cells[0].text = 'Qty'
hdr_cells[1].text = 'Id'
hdr_cells[2].text = 'Desc'
for qty, id, desc in records:
    row_cells = table.add_row().cells
    row_cells[0].text = str(qty)
    row_cells[1].text = id
    row_cells[2].text = desc

document.add_page_break()

# Create table 1
table = document.add_table(rows=1, cols=3)
hdr_cells = table.rows[0].cells
hdr_cells[0].text = 'Qty'
hdr_cells[1].text = 'Id'
hdr_cells[2].text = 'Desc'
for qty, id, desc in records:
    row_cells = table.add_row().cells
    row_cells[0].text = str(qty)
    row_cells[1].text = id
    row_cells[2].text = desc

# Create table 2
table = document.add_table(rows=1, cols=3)
hdr_cells = table.rows[0].cells
hdr_cells[0].text = 'Qty'
hdr_cells[1].text = 'Id'
hdr_cells[2].text = 'Desc'
for qty, id, desc in records:
    row_cells = table.add_row().cells
    row_cells[0].text = str(qty)
    row_cells[1].text = id
    row_cells[2].text = desc

# Print line spacing for all tables 
for index, table in enumerate(document.tables):
    print(index, table.style.paragraph_format.line_spacing)

Output:

0 None
1 None
2 None

Then I try to change the line spacing only in the final table:

table = document.tables[2]
table.style.paragraph_format.line_spacing_rule = WD_LINE_SPACING.EXACTLY
table.style.paragraph_format.line_spacing = Pt(7)

# Print line spacing for all tables
for index, table in enumerate(document.tables):
    print(index, table.style.paragraph_format.line_spacing)

Output:

0 88900
1 88900
2 88900

It has changed the line spacing for all of the tables - they are all now 7 pt (12 point is 152400). If I try to reset the line spacing in the other tables, all the tables are updated with that value.

Here is my session info:

Session info --------------------------------------------------------------------
Platform: Windows-7-6.1.7601-SP1 (64-bit)
Python: 3.7
Date: 2020-09-21
Packages ------------------------------------------------------------------------
python-docx==0.8.10
reprexpy==0.3.0

Is this a bug or am I doing something wrong?

A style is like a formatting template that you set up once and then apply to as many document objects as you want to get consistent formatting. Every object with that style applied gets that same set of formatting settings. When you adjust the table style (which all the tables appear to be sharing) you get exactly the result you're seeing.

I think what you want to be doing is setting the paragraph line spacing directly on the paragraphs only on the table in question. You could possibly set up a new paragraph style and just apply that to those paragraphs if you wanted.