Develop Reference

Map functions and regex?

I'm trying to get the domain from a list of URL's. For that, I'm using regex in a function for pattern matching.
def get_domain(url):
m = re.search(r"https:\/\/(.*)\/", url)
result = m.group(1)
return result;
string_array = ("hTTps://stack0verflow.com/", "hTTps://stackoverfl0w.com/", "hTTps://stackoverfiow.com/")
m = list(map(get_domain, string_array))
The function get_domain works if I use a for-loop to iterate over the list of strings, but whenever I try to use the map function, I get the error below.
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-23-575cbcab950e> in <module>
9 print(get_domain(url))
10
---> 11 m = list(map(get_domain, string_array))
12 ##print(m)
<ipython-input-19-fc11e511d74d> in get_domain(url)
12 def get_domain(url):
13 m = re.search(r"https:\/\/(.*)\/", url)
---> 14 result = m.group(1)
15 return result;
AttributeError: 'NoneType' object has no attribute 'group'
Why does this happen and what am I doing wrong? I've seen a lot of examples online of the map function, and I think i have the syntax down.

this regex will get only domain name in first group :
(?:https?:\/\/)?(?:(?:www|ssh).)?((?=.*\.)[^\n\/]*)
and don't forget to make it case insensitive
exemple :
import re
arr = ["https://www.exemple.com/?query=blablabla","https://www.exemple.com/aaa","hTTp://www.exemple.com","www.exemple.com/aaa","exemple.com"]
for i in arr:
m = re.search(r"(?:https?:\/\/)?(?:(?:www|ssh).)?((?=.*\.)[^\n\/]*)",i,re.IGNORECASE)
print(m.group(1))

Trying to do a simple regex

i wan to extract (abc)(def) using the regex
which i ended up with that error below
import re
def main():
str = "-->(abc)(def)<--"
match = re.search("\-->(.*?)\<--" , str).group(1)
print match
The error is:
Traceback (most recent call last):
File "test.py", line 7, in <module>
match = re.search("\-->(.*?)\<--" , str).group()
File "/usr/lib/python2.7/re.py", line 146, in search
return _compile(pattern, flags).search(string)
TypeError: expected string or buffer

Corrected:
import re
def main():
my_string = "-->(abc)(def)<--"
match = re.search("\-->(.*?)\<--" , my_string).group(1)
print match
# (abc)(def)
main()
Note, that I renamed str to my_string (do not use standard library functions as own variables!). Maybe you can still optimize your regex with lookarounds, the lazy star (.*?) can get very ineffective sometimes.

Python NLP: TypeError: not all arguments converted during string formatting

I tried the code on "Natural language processing with python", but a type error occurred.
import nltk
from nltk.corpus import brown
suffix_fdist = nltk.FreqDist()
for word in brown.words():
word = word.lower()
suffix_fdist.inc(word[-1:])
suffix_fdist.inc(word[-2:])
suffix_fdist.inc(word[-3:])
common_suffixes = suffix_fdist.items()[:100]
def pos_features(word):
features = {}
for suffix in common_suffixes:
features['endswith(%s)' % suffix] = word.lower().endswith(suffix)
return features
pos_features('people')
the error is below:
Traceback (most recent call last):
File "/home/wanglan/javadevelop/TestPython/src/FirstModule.py", line 323, in <module>
pos_features('people')
File "/home/wanglan/javadevelop/TestPython/src/FirstModule.py", line 321, in pos_features
features['endswith(%s)' % suffix] = word.lower().endswith(suffix)
TypeError: not all arguments converted during string formatting
Does anyone could help me find out where i am wrong?

suffix is a tuple, because .items() returns (key,value) tuples. When you use %, if the right hand side is a tuple, the values will be unpacked and substituted for each % format in order. The error you get is complaining that the tuple has more entries than % formats.
You probably want just the key (the actual suffix), in which case you should use suffix[0], or .keys() to only retrieve the dictionary keys.

Regex error in python

I have a string that looks like a path from which I am trying to extract 020414_001 with a regular expression I got from here.
str1 = "Test 123 <C:\User\Test\xyz\022014-101\more\stuff\022014\1> Text"
Actually I am retrieving the string from a text file so I dont have to escape it, but for testing purpose I used this string instead:
str1 = <C:\\User\\Test\\xyz\\022014-101\\more\\stuff\\022014\\1>
Here is the code I tried to match the first occuring 022014-101:
import re
p = re.compile('(?<=\\)[\d]{6}[^\\]*')
m = p.match(str1)
print m.group(0) #Line 6
It gave me this error:
Traceback (most recent call last):
File "test12.py", line 6, in <module>
print m.group(0)
AttributeError: 'NoneType' object has no attribute 'group'
How can I get the desired output 020414_001 ?
EDIT:
That did it:
import re
m = re.search(r'(?<=\\)[\d]{6}[^\\]*', str1)
print m.group(0)

How to handle AttributeError in python?

I am working through some example code which I've found on What's the most efficient way to find one of several substrings in Python?. I've changed the code to:
import re
to_find = re.compile("hello|there")
search_str = "blah fish cat dog haha"
match_obj = to_find.search(search_str)
#the_index = match_obj.start()
which_word_matched = ""
which_word_matched = match_obj.group()
Since there is now no match , I get:
Traceback (most recent call last):
File "<console>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'
What is the standard way in python to handle the scenario of no match, so as to avoid the error

match_obj = to_find.search(search_str)
if match_obj:
#do things with match_obj
Other handling will go in an else block if you need to do something even when there's no match.

Your match_obj is None because the regular expression did not match. Test for it explicitly:
which_word_matched = match_obj.group() if match_obj else ''