Building XPath Relative Expressions

Build relative expressions when passing xpath_base kword argument. The xpath of the parent should be removed so base_xpath should be like:

xpath_base = '//*[@id="math"]/parent::* | //*[@id="math"]/descendant-or-self::*'

Example:

from lxml import html
from xml2xpath import xml2xpath

filepath = 'tests/resources/html5-small.html.xml'
hdoc = html.parse(filepath)

needle = 'math'
xpath_base = f'//*[@id="{needle}"]/parent::* | //*[@id="{needle}"]/descendant-or-self::*'
xmap = xml2xpath.parse(None, itree=hdoc, xpath_base=xpath_base)[2]

rel_xpath = []
xiter = iter(xmap)
# parent xpath
x0 = next(xiter)
# base element xpath
x1 = next(xiter)
# get base element attributes and build a predicate with first
x1a = ''
if len(xmap[x1][2]) > 0:
    x1a = f'[@{xmap[x1][2][0]}="{needle}"]'
# base element relative xpath (/html/body/math -> //math)
x1f = x1.replace(x0, '/')
# remove numeric indexes if any (div[1] -> div)
x1f = x1f.split('[', 1)[0]
# add first attribute as predicate
x1f += x1a
rel_xpath.append(x1f)

# children relative xpath
for xs in list(xmap.keys())[2:]:
    rel_xpath.append(xs.replace(x1, x1f))

for x in rel_xpath:
    print(x)

Output

//math[@id='math']
//math[@id='math']/mrow
//math[@id='math']/mrow/mi
//math[@id='math']/mrow/mo
//math[@id='math']/mrow/mfrac
//math[@id='math']/mrow/mfrac/mn
//math[@id='math']/mrow/mfrac/msqrt
//math[@id='math']/mrow/mfrac/msqrt/mrow
//math[@id='math']/mrow/mfrac/msqrt/mrow/msup
//math[@id='math']/mrow/mfrac/msqrt/mrow/msup/mi
//math[@id='math']/mrow/mfrac/msqrt/mrow/msup/mn
//math[@id='math']/mrow/mfrac/msqrt/mrow/mo
//math[@id='math']/mrow/mfrac/msqrt/mrow/mn