How to download any(!) webpage with correct charset in python?
Question:
Problem
When screen-scraping a webpage using python one has to know the character encoding of the page. If you get the character encoding wrong than your output will be messed up.
People usually use some rudimentary technique to detect the encoding. They either use the charset from the header or the charset defined in the meta tag or they use an encoding detector (which does not care about meta tags or headers).
By using only one these techniques, sometimes you will not get the same result as you would in a browser.
Browsers do it this way:
- Meta tags always takes precedence (or xml definition)
- Encoding defined in the header is used when there is no charset defined in a meta tag
- If the encoding is not defined at all, than it is time for encoding detection.
(Well… at least that is the way I believe most browsers do it. Documentation is really scarce.)
What I’m looking for is a library that can decide the character set of a page the way a browser would. I’m sure I’m not the first who needs a proper solution to this problem.
Solution (I have not tried it yet…)
According to Beautiful Soup’s documentation.
Beautiful Soup tries the following encodings, in order of priority, to turn your document into Unicode:
- An encoding you pass in as the
fromEncoding argument to the soup
constructor.
- An encoding discovered in the document itself: for instance, in an XML declaration or (for HTML documents) an http-equiv META tag. If Beautiful Soup finds this kind of encoding within the document, it parses the document again from the beginning and gives the new encoding a try. The only exception is if you explicitly specified an encoding, and that encoding actually worked: then it will ignore any encoding it finds in the document.
- An encoding sniffed by looking at the first few bytes of the file. If an encoding is detected
at this stage, it will be one of the
UTF-* encodings, EBCDIC, or ASCII.
- An
encoding sniffed by the chardet
library, if you have it installed.
- UTF-8
- Windows-1252
Answers:
Use the Universal Encoding Detector:
>>> import chardet
>>> chardet.detect(urlread("http://google.cn/"))
{'encoding': 'GB2312', 'confidence': 0.99}
The other option would be to just use wget:
import os
h = os.popen('wget -q -O foo1.txt http://foo.html')
h.close()
s = open('foo1.txt').read()
When you download a file with urllib or urllib2, you can find out whether a charset header was transmitted:
fp = urllib2.urlopen(request)
charset = fp.headers.getparam('charset')
You can use BeautifulSoup to locate a meta element in the HTML:
soup = BeatifulSoup.BeautifulSoup(data)
meta = soup.findAll('meta', {'http-equiv':lambda v:v.lower()=='content-type'})
If neither is available, browsers typically fall back to user configuration, combined with auto-detection. As rajax proposes, you could use the chardet module. If you have user configuration available telling you that the page should be Chinese (say), you may be able to do better.
instead of trying to get a page then figuring out the charset the browser would use, why not just use a browser to fetch the page and check what charset it uses..
from win32com.client import DispatchWithEvents
import threading
stopEvent=threading.Event()
class EventHandler(object):
def OnDownloadBegin(self):
pass
def waitUntilReady(ie):
"""
copypasted from
http://mail.python.org/pipermail/python-win32/2004-June/002040.html
"""
if ie.ReadyState!=4:
while 1:
print "waiting"
pythoncom.PumpWaitingMessages()
stopEvent.wait(.2)
if stopEvent.isSet() or ie.ReadyState==4:
stopEvent.clear()
break;
ie = DispatchWithEvents("InternetExplorer.Application", EventHandler)
ie.Visible = 0
ie.Navigate('http://kskky.info')
waitUntilReady(ie)
d = ie.Document
print d.CharSet
It seems like you need a hybrid of the answers presented:
- Fetch the page using urllib
- Find
<meta> tags using beautiful soup or other method
- If no meta tags exist, check the headers returned by urllib
- If that still doesn’t give you an answer, use the universal encoding detector.
I honestly don’t believe you’re going to find anything better than that.
In fact if you read further into the FAQ you linked to in the comments on the other answer, that’s what the author of detector library advocates.
If you believe the FAQ, this is what the browsers do (as requested in your original question) as the detector is a port of the firefox sniffing code.
BeautifulSoup dose this with UnicodeDammit : Unicode, Dammit
I would use html5lib for this.
Scrapy downloads a page and detects a correct encoding for it, unlike requests.get(url).text or urlopen. To do so it tries to follow browser-like rules – this is the best one can do, because website owners have incentive to make their websites work in a browser. Scrapy needs to take HTTP headers, <meta> tags, BOM marks and differences in encoding names in account.
Content-based guessing (chardet, UnicodeDammit) on its own is not a correct solution, as it may fail; it should be only used as a last resort when headers or <meta> or BOM marks are not available or provide no information.
You don’t have to use Scrapy to get its encoding detection functions; they are released (among with some other stuff) in a separate library called w3lib: https://github.com/scrapy/w3lib.
To get page encoding and unicode body use w3lib.encoding.html_to_unicode function, with a content-based guessing fallback:
import chardet
from w3lib.encoding import html_to_unicode
def _guess_encoding(data):
return chardet.detect(data).get('encoding')
detected_encoding, html_content_unicode = html_to_unicode(
content_type_header,
html_content_bytes,
default_encoding='utf8',
auto_detect_fun=_guess_encoding,
)
Problem
When screen-scraping a webpage using python one has to know the character encoding of the page. If you get the character encoding wrong than your output will be messed up.
People usually use some rudimentary technique to detect the encoding. They either use the charset from the header or the charset defined in the meta tag or they use an encoding detector (which does not care about meta tags or headers).
By using only one these techniques, sometimes you will not get the same result as you would in a browser.
Browsers do it this way:
- Meta tags always takes precedence (or xml definition)
- Encoding defined in the header is used when there is no charset defined in a meta tag
- If the encoding is not defined at all, than it is time for encoding detection.
(Well… at least that is the way I believe most browsers do it. Documentation is really scarce.)
What I’m looking for is a library that can decide the character set of a page the way a browser would. I’m sure I’m not the first who needs a proper solution to this problem.
Solution (I have not tried it yet…)
According to Beautiful Soup’s documentation.
Beautiful Soup tries the following encodings, in order of priority, to turn your document into Unicode:
- An encoding you pass in as the
fromEncoding argument to the soup
constructor. - An encoding discovered in the document itself: for instance, in an XML declaration or (for HTML documents) an http-equiv META tag. If Beautiful Soup finds this kind of encoding within the document, it parses the document again from the beginning and gives the new encoding a try. The only exception is if you explicitly specified an encoding, and that encoding actually worked: then it will ignore any encoding it finds in the document.
- An encoding sniffed by looking at the first few bytes of the file. If an encoding is detected
at this stage, it will be one of the
UTF-* encodings, EBCDIC, or ASCII. - An
encoding sniffed by the chardet
library, if you have it installed. - UTF-8
- Windows-1252
Use the Universal Encoding Detector:
>>> import chardet
>>> chardet.detect(urlread("http://google.cn/"))
{'encoding': 'GB2312', 'confidence': 0.99}
The other option would be to just use wget:
import os
h = os.popen('wget -q -O foo1.txt http://foo.html')
h.close()
s = open('foo1.txt').read()
When you download a file with urllib or urllib2, you can find out whether a charset header was transmitted:
fp = urllib2.urlopen(request)
charset = fp.headers.getparam('charset')
You can use BeautifulSoup to locate a meta element in the HTML:
soup = BeatifulSoup.BeautifulSoup(data)
meta = soup.findAll('meta', {'http-equiv':lambda v:v.lower()=='content-type'})
If neither is available, browsers typically fall back to user configuration, combined with auto-detection. As rajax proposes, you could use the chardet module. If you have user configuration available telling you that the page should be Chinese (say), you may be able to do better.
instead of trying to get a page then figuring out the charset the browser would use, why not just use a browser to fetch the page and check what charset it uses..
from win32com.client import DispatchWithEvents
import threading
stopEvent=threading.Event()
class EventHandler(object):
def OnDownloadBegin(self):
pass
def waitUntilReady(ie):
"""
copypasted from
http://mail.python.org/pipermail/python-win32/2004-June/002040.html
"""
if ie.ReadyState!=4:
while 1:
print "waiting"
pythoncom.PumpWaitingMessages()
stopEvent.wait(.2)
if stopEvent.isSet() or ie.ReadyState==4:
stopEvent.clear()
break;
ie = DispatchWithEvents("InternetExplorer.Application", EventHandler)
ie.Visible = 0
ie.Navigate('http://kskky.info')
waitUntilReady(ie)
d = ie.Document
print d.CharSet
It seems like you need a hybrid of the answers presented:
- Fetch the page using urllib
- Find
<meta>tags using beautiful soup or other method - If no meta tags exist, check the headers returned by urllib
- If that still doesn’t give you an answer, use the universal encoding detector.
I honestly don’t believe you’re going to find anything better than that.
In fact if you read further into the FAQ you linked to in the comments on the other answer, that’s what the author of detector library advocates.
If you believe the FAQ, this is what the browsers do (as requested in your original question) as the detector is a port of the firefox sniffing code.
BeautifulSoup dose this with UnicodeDammit : Unicode, Dammit
I would use html5lib for this.
Scrapy downloads a page and detects a correct encoding for it, unlike requests.get(url).text or urlopen. To do so it tries to follow browser-like rules – this is the best one can do, because website owners have incentive to make their websites work in a browser. Scrapy needs to take HTTP headers, <meta> tags, BOM marks and differences in encoding names in account.
Content-based guessing (chardet, UnicodeDammit) on its own is not a correct solution, as it may fail; it should be only used as a last resort when headers or <meta> or BOM marks are not available or provide no information.
You don’t have to use Scrapy to get its encoding detection functions; they are released (among with some other stuff) in a separate library called w3lib: https://github.com/scrapy/w3lib.
To get page encoding and unicode body use w3lib.encoding.html_to_unicode function, with a content-based guessing fallback:
import chardet
from w3lib.encoding import html_to_unicode
def _guess_encoding(data):
return chardet.detect(data).get('encoding')
detected_encoding, html_content_unicode = html_to_unicode(
content_type_header,
html_content_bytes,
default_encoding='utf8',
auto_detect_fun=_guess_encoding,
)