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Finds Forms in HTML using Python and regular expression

I have the following code that checks if there is a formular content in an email body but I did not understand what does this string '<\s?\/?\s?form\s?>' means and if there is another method to check formular content existence in an email?
This is the code I wrote:
class HTMLFormFinder(FeatureFinder):
def getFeature(self, message):
import re
super(HTMLFormFinder, self).getFeature(message)
payload = utils.getpayload(message).lower()
return re.compile(r'<\s?\/?\s?form\s?>', re.IGNORECASE).search(payload)!= None
Thanks in advance.

It's what's called a regular expression. It's a way to match strings that follow a particular pattern.
https://docs.python.org/3.7/library/re.html
Here r'<\s?\/?\s?form\s?>' describes a <form> HTML tag with several fallbacks in case of bad/malformed html, specifically it handles whitespaces that may appear beside the tag name form.
A better way of checking the presence of forms is to use an XML/HTML parser, like ElementTree, BeautifulSoup, because they handle bad/incorrect HTML much better than regular expressions ever can. But if you want to keep it simple, the regex you have should suffice.
https://docs.python.org/3.7/library/xml.etree.elementtree.html
https://www.crummy.com/software/BeautifulSoup/bs4/doc/
Using BeautifulSoup you can do:
from bs4 import BeautifulSoup
soup = BeautifulSoup(html)
has_form = len(soup.find('form')) > 0

You can read more on regular expressions here:
https://docs.python.org/2/library/re.html
Specifically \s matches any whitespace charachter.

Python RegEx for this HTML String

I've got a string which is like that:
<span class=\"market_listing_price market_listing_price_with_fee\">\r
\t\t\t\t\t$92.53 USD\t\t\t\t<\/span>
I need to find this string via RegEx. My try:
(^<span class=\\"market_listing_price market_listing_price_with_fee\\">\\r\\t\\t\\t\\t\\t&)
But my problem is, the count of "\t" and "\r" may vary.. And of course this is not the Regular Expression for the whole string.. Only for a part of it.
So, what's the correct and full RegEx for this string?

Answering your question about the Regex:
"market_listing_price market_listing_price_with_fee\\">[\\r]*[\\t]*&
This will catch the string you need. Even if you add more \t's or \r's.
If you need to edit this Regex I advice you to visit this website and test-modify it. It will also help you to understand how regular expression works and build your own complete RegEx.

Since this is an HTML string, I would suggest using an HTML Parser like BeautifulSoup.
Here is an example approach finding the element by class attribute value using a CSS selector:
from bs4 import BeautifulSoup
data = "my HTML data"
soup = BeautifulSoup(data)
result = soup.select("span.market_listing_price.market_listing_price_with_fee")
See also:
RegEx match open tags except XHTML self-contained tags

Extract string using regex

How can I extract the content (how are you) from the string:
<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">how are you</string>.
Can I use regex for the purpose? if possible whats suitable regex for it.
Note: I dont want to use split function for extract the result. Also can you suggest some links to learn regex for a beginner.
I am using python2.7.2

You could use a regular expression for this (as Joey demonstrates).
However if your XML document is any bigger than this one-liner you could not since XML is not a regular language.
Use BeautifulSoup (or another XML parser) instead:
>>> from BeautifulSoup import BeautifulSoup
>>> xml_as_str = '<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">how are you</string>. '
>>> soup = BeautifulSoup(xml_as_str)
>>> print soup.text
how are you.
Or...
>>> for string_tag in soup.findAll('string'):
... print string_tag.text
...
how are you

Try with following regex:
/<[^>]*>(.*?)</

(?<=<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/">)[^<]+(?=</string>)
would match what you want, as a trivial example.
(?<=<)[^<]+
would, too. It all depends a bit on how your input is formatted exactly.

This will match a generic HTML tag (Replace "string" with the tag you want to match):
/<string[^<]*>(.*?)<\/string>/i
(i=case insensitive)

Match "without this"

I need to remove all <p></p> that are only <p>'s in <td>.
But how it can be done?
import re
text = """
<td><p>111</p></td>
<td><p>111</p><p>222</p></td>
"""
text = re.sub(r'<td><p>(??no</p>inside??)</p></td>', r'<td>\1</td>', text)
How can I match without</p>inside?

I would use minidom. I stole the following snippet from here which you should be able to modify and work for you:
from xml.dom import minidom
doc = minidom.parse(myXmlFile)
for element in doc.getElementsByTagName('MyElementName'):
if element.getAttribute('name') in ['AttrName1', 'AttrName2']:
parentNode = element.parentNode
parentNode.insertBefore(doc.createComment(element.toxml()), element)
parentNode.removeChild(element)
f = open(myXmlFile, "w")
f.write(doc.toxml())
f.close()
Thanks #Ivo Bosticky

While using regexps with HTML is bad, matching a string that does not contain a given pattern is an interesting question in itself.
Let's assume that we want to match a string beginning with an a and ending with a z and take out whatever is in between only when string bar is not found inside.
Here's my take: "a((?:(?<!ba)r|[^r])+)z"
It basically says: find a, then find either an r which is not preceded by ba, or something different than r (repeat at least once), then find a z. So, a bar cannot sneak in into the catch group.
Note that this approach uses a 'negative lookbehind' pattern and only works with lookbehind patterns of fixed length (like ba).

I would definitely recommend using BeautifulSoup for this. It's a python HTML/XML parser.
http://www.crummy.com/software/BeautifulSoup/

Not quite sure why you want to remove the P tags which don't have closing tags.
However, if this is an attempt to clean code, an advantage of BeautifulSoup is that is can clean HTML for you:
from BeautifulSoup import BeautifulSoup
html = """
<td><p>111</td>
<td><p>111<p>222</p></td>
"""
soup = BeautifulSoup(html)
print soup.prettify()
this doesn't get rid of your unmatched tags, but it fixes the missing ones.

Extracting some HTML tag values in Python

How to get a value of nested <b> HTML tag in Python using regular expressions?
<b>LG</b> X110
# => LG X110

You don't.
Regular Expressions are not well suited to deal with the nested structure of HTML. Use an HTML parser instead.

Don't use regular expressions for parsing HTML. Use an HTML parser like BeautifulSoup. Just look how easy it is:
from BeautifulSoup import BeautifulSoup
html = r'<b>LG</b> X110'
soup = BeautifulSoup(html)
print ''.join(soup.findAll(text=True))
# LG X110

Your question was very hard to understand, but from the given output example it looks like you want to strip everything within < and > from the input text. That can be done like so:
import re
input_text = '<a bob>i <b>c</b></a>'
output_text = re.sub('<[^>]*>', '', input_text)
print output_text
Which gives you:
i c
If that is not what you want, please clarify.
Please note that the regular expression approach for parsing XML is very brittle. For instance, the above example would break on the input <a name="b>c">hey</a>. (> is a valid character in a attribute value: see XML specs)

Try this...
<a.*<b>(.*)</b>(.*)</a>
$1 and $2 should be what you want, or whatever means Python has for printing captured groups.

+1 for Jens's answer. lxml is a good library you can use to actually parse this in a robust fashion. If you'd prefer something in the standard library, you can use sax, dom or elementree.