find_all() and select() behave differently on markup containing duplicate elements

[BLKSerene]

While find_all() can find all duplicate elements, select() cannot.
I'm using Python 3.6.2 with BeautifulSoup 4.6.2 and lxml parser

The test snippet:

import os

from bs4 import BeautifulSoup

markup = '<span class="test1">test1</span><span class="test2">test2</span><span class="test3">test3</span><span class="test1">test1</span>'
soup = BeautifulSoup(markup, 'lxml')

print('find_all:')
for element in soup.find_all(class_ = ['test1', 'test2', 'test3']):
 print(element) # Print 4 elements including duplicate elements
print('Length of "find_all": ' + str(len(soup.find_all(class_ = ['test1', 'test2', 'test3']))))

print('select:')
for element in soup.select('.test1, .test2, .test3'):
 print(element) # Print only 3 elements
print('Length of "select": ' + str(len(soup.select('.test1, .test2, .test3'))))

os.system('pause')

[Leonard Richardson (leonardr)]

Thanks for reporting this bug and providing an easy way to duplicate it. The CSS selector system is contributed code and for my own sanity I only add to it when a patch and test are contributed. I'm going to leave this issue open in a 'confirmed' state and if someone provides a patch or pull request I'll merge it.

[BLKSerene (blkserene-deactivatedaccount-deactivatedaccount)]

I've found the problem.

In element.py:
remove line 1357 'if candidate not in context:'
I tested it again and the bug has disappeared.

[Leonard Richardson (leonardr)]

Thanks for isolating the part that needs to be changed. Revision 472 fixes this behavior.