Why doesn't checking an attribute's value imply that the attribute exists?
Question
While using BeautifulSoup I very often have to condition some action on the value of a tag's class. For example, imagine that I want to do some action on <p> only when the attribute is class="box" , and a different action otherwise. What I do is:
soup = BeautifulSoup('''
<html><body>
<h1>Titolo</h1>
<p>Testo che sta sotto il titolo</p>
<p class="sidenote">Questo da stampare</p>
<p>Questo è il testo della nota marginale</p>
</body></html>
''',"lxml")
for sel in soup.body:
if not isinstance(sel,NavigableString) and \
"class" in sel.attrs and "sidenote" in sel["class"]:
print(sel)
else
print("not found")
This is a bit clumsy. I wonder if there's a way to make the condition a little more compact than this. The ideal would be that a check on the final condition (that class contains sidenote ) implied that the element does have a class attribute and, consequently, it is a tag, not a NavigableString.
2 answers
solution1
0 2017-11-30 21:31:41
Using a ternary operator would definitely remove some bulk, though not everything at once. The number of if-else's would still be same though. So, not sure if that would work for you.
http://book.pythontips.com/en/latest/ternary_operators.html
So the current code would become:
if "class" in div.attrs:
div.do_something if "box" in div["class"] else div.do_something_else
else:
div.do_something_else
or if you want to compress it further (though I feel that would affect readability):
(div.do_something if "box" in div["class"] else div.do_something_else) if "class" in div.attrs else div.do_something_else
solution2
0 2017-11-30 22:13:18
Like for Python dictionaries, you can use the get method instead of accessing the element using [...] . This way, it does not raise a KeyError if the element is not present but just returns None . Also, you can provide a default value, so you can simplify the code to:
for sel in soup.body:
if not isinstance(sel,NavigableString) and \
"sidenote" in sel.get("class", []):
print(sel)
else
print("not found")
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