When a Tag is copied, multi-valued attribute value lists are not deeply copied

[Chris Papademetrious]

When a tag is copied with copy.copy() or the private _clone() method, multi-valued attribute value lists are not deeply copied. As a result, changes to a copied tag's value list also affect the original tag.

In this example, p1 is copied to p2, then a change to p1's "class" attribute affects p2:

====
import bs4
import copy

html_doc = '<p class="foo"/>'
soup = bs4.BeautifulSoup(html_doc, "lxml")
p1 = soup.find("p")
p2 = p1._clone()
p1.attrs["class"].append("BAR") # <-- also affects p2

print(f"p1: {p1}")
print(f"p2: {p2}")
====

Perhaps the value lists need to be copied using [:] syntax (or something similar).

[Leonard Richardson (leonardr)]

A good catch. This is fixed in revision 4aaacc0.

[Chris Papademetrious (chrispitude)]

Awesome - thanks Leonard!