我想exceptions处理“列表索引超出范围”。

I am using BeautifulSoup and parsing some HTMLs.

I’m getting a certain data from each HTML (using for loop) and adding that data to a certain list.

The problem is, some of the HTMLs have different format (and they don’t have the data that I want in them).

So, I was trying to use exception handling and add value null to the list (I should do this since the sequence of data is important.)

For instance, I have a code like:

soup = BeautifulSoup(links)
dlist = soup.findAll('dd', 'title')
# I'm trying to find content between <dd class='title'> and </dd>
gotdata = dlist[1]
# and what i want is the 2nd content of those
newlist.append(gotdata)
# and I add that to a newlist

and some of the links don’t have any <dd class='title'>, so what I want to do is add string null to the list instead.

The error appears:

list index out of range.

What I have done tried is to add some lines like this:

if not dlist[1]:  
   newlist.append('null')
   continue

But it doesn’t work out. It still shows error:

list index out of range.

What should I do about this? Should I use exception handling? or is there any easier way?

Any suggestions? Any help would be really great!

Handling the exception is the way to go:

try:
    gotdata = dlist[1]
except IndexError:
    gotdata = 'null'

Of course you could also check the len() of dlist; but handling the exception is more intuitive.

You have two options; either handle the exception or test the length:

if len(dlist) > 1:
    newlist.append(dlist[1])
    continue

or

try:
    newlist.append(dlist[1])
except IndexError:
    pass
continue

Use the first if there often is no second item, the second if there sometimes is no second item.

A ternary will suffice. change:

gotdata = dlist[1]

to

gotdata = dlist[1] if len(dlist) > 1 else 'null'

this is a shorter way of expressing

if len(dlist) > 1:
    gotdata = dlist[1]
else: 
    gotdata = 'null'

Taking reference of ThiefMaster♦ sometimes we get an error with value given as ‘\n’ or null and perform for that required to handle ValueError:

Handling the exception is the way to go

try:
    gotdata = dlist[1]
except (IndexError, ValueError):
    gotdata = 'null'

for i in range (1, len(list))
    try:
        print (list[i])

    except ValueError:
        print("Error Value.")
    except indexError:
        print("Erorr index")
    except :
        print('error ')

For anyone interested in a shorter way:

gotdata = len(dlist)>1 and dlist[1] or 'null'

But for best performance, I suggest using False instead of 'null', then a one line test will suffice:

gotdata = len(dlist)>1 and dlist[1]