更好的尝试方式-多次检查除外

Question

Suppose I have some (simplified) BeautifulSoup code like this, pulling data into a dictionary:

tournament_info = soup.find_all('li')

stats['Date'] = tournament_info[0].text
stats['Location'] = tournament_info[1].text
stats['Prize'] = tournament_info[3].text.split(':')[1].strip()

In the case where the initial find_all returns an exception, I want all the dictionary entries to be 'None'. And in the case of any of the individual dictionary assignments returning an exception, I want 'None' too.

Is there any nice way to write this, other than something horrible like below?

try:
    tournament_info = soup.find_all('li')
except:
    m_stats['Date'] = 'None'
    m_stats['Location'] = 'None'
    m_stats['Prize'] = 'None'

try:
    m_stats['Date'] = tournament_info[0].text
except:
    m_stats['Date'] = 'None'
try:
    m_stats['Location'] = tournament_info[1].text
except:
    m_stats['Location'] = 'None'
try:
    m_stats['Prize'] = tournament_info[3].text.split(':')[1].strip()
except:
    m_stats['Prize'] = 'None'

Answer 1

Here's what I can suggest for your code:

info = soup.find_all('li')
if not info:
    m_stats = dict.fromkeys(m_stats, None)
    return

mappings = {
    'Date': 0,
    'Location': 1,
    'Prize': 3
}
for key in mappings:
    value = None
    try:
        value = info[mappings[key]].text
        if mappings[key] == 3:
            value = value.split(':')[1].strip()
    except IndexError:
        pass
    m_stats[key] = value

Alternatively, you can create a function that will handle the exceptions for you:

def get_value(idx):
    value = None
    try:
        value = info[idx].text
    except IndexError:
        pass
    return value

m_stats['Date'] = get_value(0)
m_stats['Location'] = get_value(1)
m_stats['Prize'] = get_value(3)
if m_stats['Prize']:
    m_stats['Prize'].split(':')[1].strip()

Answer 2

Create own class

class Stats(dict):

    tournament_info = []

    def __init__(self, tournament_info, **kwargs):
        super(Stats, self).__init__(**kwargs)
        self.tournament_info = tournament_info
        self['Date'] = self.get_tournament_info_text(0)
        self['Location'] = self.get_tournament_info_text(1)
        prize = self.get_tournament_info_text(2)
        if prize is not None:
            prize = prize.split(':')[1].strip()
        self['Prize'] = prize

    def get_tournament_info_text(self, index):
        try:
            return self.tournament_info[index]['text']
        except:
            return None

tournament_info = [
    {
        'text': 'aaa'
    },
    {},
    {
        'text': 'bbb:ccc '
    }
]

m_stats = Stats(tournament_info)
print m_stats

Answer 3

The solution I went for was to create a blank template dictionary (actually a JSON) with all the keys set to 'None'.

Every time the page is scraped, m_stats is first initialised with this blank dictionary (loaded from the JSON). If an exception occurs, it is just simply passed (with some logging), and the value is left as 'None'. There is then no need to explicitly assign 'None' every single time.

Not sure if it's correct to mark this as the "answer", as it is quite specific to my needs, but that's what I did anyway.