Here is an example of cropping SVG throgh viewBox attribute.

def verify_bbox(bbox):
    if not isinstance(bbox, (tuple, list)):
        raise TypeError(f"Bounding box should be a tuple or list, got {type(bbox)}")
    if len(bbox) != 4:
        raise ValueError(f"Bounding box should have 4 values [left, top, right, bottom], got {len(bbox)}")
    for b in bbox:
        if not isinstance(b,(int,float)) or b < 0 or b > 1:
            raise ValueError(f"Bounding box values should be between 0 and 1, got {b}")

def crop_svg(svg, bbox):
    verify_bbox(bbox) # left, top, right, bottom in 0-1 range

    def crop_viewbox(m):
        vb, *_ = m.groups()
        x,y,w,h = [int(v) for v in vb.split()]

        X, Y = bbox[0]*w + x, bbox[1]*h + y # offset by original viewbox
        W, H = (bbox[2] - bbox[0])*w, (bbox[3] - bbox[1])*h
        return m.group().replace(vb, f'{X} {Y} {W} {H}') # Replace viewbox with new values
    
    return re.sub(r'viewBox\=[\"\'](.*?)[\"\']', crop_viewbox, svg ,1)

svg = '''<svg xmlns="http://www.w3.org/2000/svg" height="50px" viewBox="0 0 25 25" fill="red" stroke-width="2" transform="rotate(45)">\n    <rect x="9" y="0" width="8" height="6"/>\n    <rect x="9" y="7" width="1" height="10"/>\n    <rect x="12" y="7" width="2" height="10"/>\n    <rect x="16" y="7" width="1" height="10"/>\n    <polygon points="9 18,17 18,13 25,9 18"></polygon>\n</svg>'''

crop_svg(svg, [0.5,0,1,1])
'<svg xmlns="http://www.w3.org/2000/svg" height="50px" viewBox="12.5 0 12.5 25" fill="red" stroke-width="2" transform="rotate(45)">\n    <rect x="9" y="0" width="8" height="6"/>\n    <rect x="9" y="7" width="1" height="10"/>\n    <rect x="12" y="7" width="2" height="10"/>\n    <rect x="16" y="7" width="1" height="10"/>\n    <polygon points="9 18,17 18,13 25,9 18"></polygon>\n</svg>'

There are two things to be noted:

• Cropping occurs along rotated viewBox, not on x,y.
• One of height or width should be 'auto' or missing to view correctly or both reset accordingly. You can add following line:

re.sub(r'height\=[\"\'](.*?)[\"\']', 'height="auto"', svg,1)