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In this function I'm parsing the page of the item in the online shop. Some items lack the picture, some lack price etc, so there are few if-else checks.

My questions are:

  1. How to get rid of these ugly if-else checks?
  2. How I can "pythonize" my code further?
  3. Is it correct? I.e when I manipulate the variable value using previously assigned value:

    name = soup.find('span',{"class":"project_name"})
    if name is not None:
        name = re.sub(r'[«,»]','', name.text)

Below is my full code:

def grab_properties(url,html):
    soup = BeautifulSoup(html)
    link = soup.find('iframe', {"src":""})

    if link is not None:
        link = link.get("src")
        id = re.match(".*\[(\w+)\].*", link).group(1)
        if id is not None:
            if id not in ids:
                name = soup.find('span',{"class":"project_name"})
                if name is not None:
                    name = re.sub(r'[«,»]','', name.text)
                    if (soup.find('img',{"id":"item0image"}) is not None):
                        img_url = soup.find('img',{"id":"item0image"}).get('src')
                        price = soup.find('span',{"class":"project_price"})
                        if price is not None:
                            price = price.text
                            price = re.sub(u'[руб,\., ]','', price)
                            price =u"Call us!"
                        return [id.encode('utf8'), name.encode('utf8'), url.encode('utf8'), img_url.encode('utf8'), price.encode('utf8')]
share|improve this question
Welcome to CodeReview.SE! I think we are missing the definition for (at least) ids. Am I right ? – Josay May 6 '14 at 10:14
Yes, this is a global variable to control which items have been already added to the output file. I only pasted code for the function to make it easier to follow the logic. – Timofey May 6 '14 at 12:23
up vote 5 down vote accepted

You cannot get rid of those if-else checks, but you can get rid of the nesting. For example:

if foo:
    if bar:
        return foo + bar

could be flattened to

if not foo:
    return None
if not bar:
    return None
return foo + bar

While this is is in fact longer, such code tends to be easier to read.

If we apply that to your code (and fix some style issues like putting a space after each comma), then we end up with:

def grab_properties(url, html):
    soup = BeautifulSoup(html)

    link = soup.find('iframe', {"src": ""})
    if link is None:
        return None
    link = link.get("src")

    id = re.match(".*\[(\w+)\].*", link).group(1)
    if (id is None) or (id in ids):
        return None

    name = soup.find('span', {"class": "project_name"})
    if name is None:
        return None
    name = re.sub(r'[«,»]', '', name.text)

    image_element = soup.find('img', {"id": "item0image"})
    if image_element is None:
        return None
    img_url = image_element.get('src')

    price = soup.find('span', {"class": "project_price"})
    if price is None:
        price = u"Call us!"
        price = re.sub(u'[руб,\., ]', '', price.text)

    return [attr.encode('utf8') for atr in (id, name, url, img_url, price)]

Notice that I created the image_element variable to avoid searching for the same element multiple times, that I used a list comprehension to encode various strings to UTF-8, and that I used empty lines to separate the code for unrelated attributes, thus making the code easier to understand. I also swapped the if price is not None condition around to avoid a confusing negation.

We should now talk about regular expressions (see also the re library documentation). The […] is a character class. It matches any of the contained characters, so [abc] will match either a or b or c, but not the whole string abc. The comma is not special inside a character class, so [«,»] will match left or right guillemets, or a comma. To match just the angled quotation marks, use [«»]. Similarly, [руб,\., ] will match either р or у or б or a comma or a period or a space. Note that inside a character class, the period is not a metacharacter and does not have to be escaped. So that charclass would be equivalent to [р,у б.] (the order of characters does not matter). If you want to match alternative patterns, use the | regex operator: руб|[. ], which matches either the substring руб or a period or a space.

You could also consider precompiling your regular expressions, which might improve performance if you call your function very often:

RE_GUILLEMETS = re.compile('[«»]')

def ...:
    name = RE_GUILLEMETS.sub('', name.text)
share|improve this answer
Than you for such a detailed answer! – Timofey May 6 '14 at 12:38

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