re.findall() hangs in python

[silverburgh.meryl]

Hi,

I have the following regular expression.
It works when 'data' contains the pattern and I see 'match2' get print
out.
But when 'data' does not contain pattern, it just hangs at
're.findall'

pattern = re.compile("(.*)<img (.*?) src=\"(.*?)img(.*?)\"(.*?)",
re.S)

print "before find all"

match = re.findall(pattern, data)

if (match):
print "match2"



Can you please tell me why it that?

 

[Peter Otten]

I have the following regular expression.
It works when 'data' contains the pattern and I see 'match2' get print
out.
But when 'data' does not contain pattern, it just hangs at
're.findall'

pattern = re.compile("(.*)<img (.*?) src=\"(.*?)img(.*?)\"(.*?)",
re.S)

print "before find all"

match = re.findall(pattern, data)

if (match):
print "match2"



Can you please tell me why it that?

Could it be that it is just slow? If not, post a small example of data that
provokes findall() to hang.

Peter

 

[7stud]

Hi,

I have the following regular expression.
It works when 'data' contains the pattern and I see 'match2' get print
out.
But when 'data' does not contain pattern, it just hangs at
're.findall'

pattern = re.compile("(.*)<img (.*?) src=\"(.*?)img(.*?)\"(.*?)",
re.S)

print "before find all"

match = re.findall(pattern, data)

if (match):
print "match2"

Can you please tell me why it that?

It doesn't hang when I try it. Why don't you post a complete example
that hangs.

Also, you might consider using exterior single quotes around your
string so that you don't have to escape double quotes inside the
string.

 

[Gabriel Genellina]

Could it be that it is just slow? If not, post a small example of data
that
provokes findall() to hang.

I bet it is very slooooooow!
To the OP: do you actually need all those groups? Specially the first and
last (.*), they match all the surrounding text.

 

[irstas]

But when 'data' does not contain pattern, it just hangs at
're.findall'

pattern = re.compile("(.*)<img (.*?) src=\"(.*?)img(.*?)\"(.*?)",
re.S)

That pattern is just really slow to evaluate. What you want is
probably something more like this:

re.compile(r'<img [^>]*src\s*=\s*"([^"]*img[^"]*)"')

"dot" is usually not so great. Prefer "NOT end-character", like [^>]
or [^"].

 

[silverburgh.meryl]

But when 'data' does not contain pattern, it just hangs at
're.findall'

pattern = re.compile("(.*)<img (.*?) src=\"(.*?)img(.*?)\"(.*?)",
re.S)

That pattern is just really slow to evaluate. What you want is
probably something more like this:

re.compile(r'<img [^>]*src\s*=\s*"([^"]*img[^"]*)"')

"dot" is usually not so great. Prefer "NOT end-character", like [^>]
or [^"].

Thank you. Your suggestion solves my problem!