Python-docx, how to set cell width in tables?

Short answer: set cell width individually.

for cell in table.columns[0].cells:
    cell.width = Inches(0.5)

python-docx does what you tell it to do when you set column width. The problem is that Word ignores it. Other clients, like LibreOffice, respect the column width setting.

A .docx file is in XML format (hence the ‘x’ suffix in the file extension). The XML vocabulary for tables has a place for column width and a place for cell width. Who pays attention to what is a bit vexed when it comes to this detail. The one common denominator is that everyone respects explicit widths set at the individual cell level. It doesn’t make a lot of sense to me, but this is what it takes to make it work. It might make sense to have a function in your program that takes care of the details:

def set_col_widths(table):
    widths = (Inches(1), Inches(2), Inches(1.5))
    for row in table.rows:
        for idx, width in enumerate(widths):
            row.cells[idx].width = width

This gets a bit more complicated if your table has merged cells, which could actually be the reason Word ignores column widths; they’re ambiguous in certain merged-cell situations.