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I am new to Python (I dont have any programming training either), so please keep that in mind as I ask my question.
I am trying to search a retrieved webpage and find all links using a specified pattern. I have done this successfully in other scripts, but I am getting an error that says
raise error, v # invalid expressionsre_constants.error: multiple repeat
I have to admit I do not know why, but again, I am new to Python and Regular Expressions. However, even when I don't use patterns and use a specific link (just to test the matching), I do not believe I return any matches (nothing is sent to the window when I print match.group(0). The link I tested is commented out below.
Any ideas? It usually is easier for me to learn by example, but any advice you can give is greatly appreciated!
Brock
import urllib2
from BeautifulSoup import BeautifulSoup
import re
url = "http://forums.epicgames.com/archive/index.php?f-356-p-164.html"
page = urllib2.urlopen(url).read()
soup = BeautifulSoup(page)
pattern = r'<a href="http://forums.epicgames.com/archive/index.php?t-([0-9]+).html">(.?+)</a> <i>((.?+) replies)'
#pattern = r'href="http://forums.epicgames.com/archive/index.php?t-622233.html">Gears of War 2: Horde Gameplay</a> <i>(20 replies)'
for match in re.finditer(pattern, page, re.S):
print match(0)
236
To match a character having special meaning in regex, you need to use a escape sequence prefix with a backslash ( \ ). E.g., \. matches "." ; regex \+ matches "+" ; and regex \( matches "(" . You also need to use regex \\ to match "\" (back-slash).
match() function of re in Python will search the regular expression pattern and return the first occurrence. The Python RegEx Match method checks for a match only at the beginning of the string. So, if a match is found in the first line, it returns the match object.
Matches(String, Int32) Searches the specified input string for all occurrences of a regular expression, beginning at the specified starting position in the string. Matches(String) Searches the specified input string for all occurrences of a regular expression.
Avoid coding in regex if you can In programming, only use regular expressions as a last resort. Don't solve important problems with regex. regex is expensive – regex is often the most CPU-intensive part of a program. And a non-matching regex can be even more expensive to check than a matching one.
That means your regular expression has an error.
(.?+)</a> <i>((.?+)
What does ?+ mean? Both ? and + are meta characters that does not make sense right next to each other. Maybe you forgot to escape the '?' or something.
133
You need to escape the literal '?' and the literal '(' and ')' that you are trying to match.
Also, instead of '?+', I think you're looking for the non-greedy matching provided by '+?'.
More documentation here.
For your case, try this:
pattern = r'<a href="http://forums.epicgames.com/archive/index.php\?t-([0-9]+).html"> (.+?)</a> <i>\((.+?) replies\)'
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