On 25/11/15 23:48, ryguy7272 wrote:
re.findall( r'\<a[^>]+title="(.+?)"', html )
[ ... ]
Thanks!! Is that regex? Can you explain exactly what it is doing?
Also, it seems to pick up a lot more than just the list I wanted, but that's
ok, I can see why it does that.
Can you just please explain what it's doing???
Yes it's a regular expression. Because RegEx's use the backslash as an
escape character, it is advisable to use the "raw string" prefix (r
before single/double/triple quote. To illustrate it with an example :
>>> print "1\n2"
1
2
>>> print r"1\n2"
1\n2
As the backslash escape character is "neutralized" by the raw string,
you can use the usual RegEx syntax at leisure :
\<a[^>]+title="(.+?)"
\< was a mistake on my part, a single < is perfectly enough
[^>] is a class definition, and the caret (^) character indicates
negation. Thus it means : any character other than >
+ incidates repetition : one or more of the previous element
. will match just anything
.+" is a _greedy_ pattern that would match anything until it encountered
a double quote
The problem with a greedy pattern is that it doesn't stop at the first
match. To illustrate :
>>> a = re.search( r'".+"', 'title="this is a test" class="test"' )
>>> a.group()
'"this is a test" class="test"'
It matches the first quote up to the last one.
On the other hand, you can use the "?" modifier to specify a non-greedy
pattern :
>>> b = re.search( r'".+?"', 'title="this is a test" class="test"' )
'"this is a test"'
It matches the first quote and stops looking for further matches after
the second quote.
Finally, the parentheses are used to indicate a capture group :
>>> a = re.search( r'"this (is) a (.+?)"', 'title="this is a test"
class="test"' )
>>> a.groups()
('is', 'test')
You can find detailed explanations about Python regular expressions at
this page : https://docs.python.org/2/howto/regex.html
HTH,
-Grobu-
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