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To Split text based on words using python code

I have a long text like the one below. I need to split based on some words say ("In","On","These")
Below is sample data:
On the other hand, we denounce with righteous indignation and dislike men who are so beguiled and demoralized by the charms of pleasure of the moment, so blinded by desire, that they cannot foresee the pain and trouble that are bound to ensue; and equal blame belongs to those who fail in their duty through weakness of will, which is the same as saying through shrinking from toil and pain. These cases are perfectly simple and easy to distinguish. In a free hour, when our power of choice is untrammelled and when nothing prevents our being able to do what we like best, every pleasure is to be welcomed and every pain avoided. But in certain circumstances and owing to the claims of duty or the obligations of business it will frequently occur that pleasures have to be repudiated and annoyances accepted. The wise man therefore always holds in these matters to this principle of selection: he rejects pleasures to secure other greater pleasures, or else he endures pains to avoid worse pains.
Can this problem be solved with a code as I have 1000 rows in a csv file.

As per my comment, I think a good option would be to use regular expression with the pattern:
re.split(r'(?<!^)\b(?=(?:On|In|These)\b)', YourStringVariable)

Yes this can be done in python. You can load the text into a variable and use the built in Split function for string. For example:
with open(filename, 'r') as file:
lines = file.read()
lines = lines.split('These')
# lines is now a list of strings split whenever 'These' string was encountered

To find whole words that are not part of larger words, I like using the regular expression:
[^\w]word[^\w]
Sample python code, assuming the text is in a variable named text:
import re
exp = re.compile(r'[^\w]in[^\w]', flags=re.IGNORECASE)
all_occurrences = list(exp.finditer(text))

Creating a dictionary in Python and using it to translate a word

I have created a Spanish-English dictionary in Python and I have stored it using the variable translation. I want to use that variable in order to translate a text from Spanish into English. This is the code I have used so far:
from corpus.nltk import swadesh
import my_books
es2en = swadesh.entries(['es', 'en'])
translation = dict(es2en)
for sentence in my_books.sents("book_1"):
for word in my_books.words("book_1"):
if word in es2en:
print(translation, end= " ")
else:
print("unknown_word", end= " ")
print("")
My problem is that none of the words in book_1 is actually translated into English, so I get a text full of unknown word. I think I'm probably using translation in the wrong way... how could I achieve my desired result?

The .entries() method, when given more than one language, returns not a dictionary but a list of tuples. See here for an example.
You need to convert your list of pairs (2-tuples) into a dictionary. You are doing that with your translation = statement.
However, you then ignore the translation variable, and check for if word in es2en:
You need to check if the word is in translation, and subsequently look up the correct translation, instead of printing the entire dictionary.

It can be a 'Case Sensitivity' issue.
For Example:
If a dict contain a key 'Bomb' and you will look for 'bomb',
it won't be found.
Lower all the keys at es2en and then look for:word.lower() in es2en

i am in progress build a translate machine (language dictionary).
it's in bahasa (indonesia) to english and vice versa.
I build it from zero, what i'm doing is collecting all words in bahasa, and the means of the words.
then compare it with wordnet database (crawl it).
after have a group of meaning and already pairing / grouping the meaning in english with the bahasa, do this, collecting ad many as data, separate it, scienting content and daily content.
tokenize all data in to sentence, make a calculation which word is more high probabilty pairing with other word (both in bahasa and english), this is needed because every words could have several means. this calculation use to choose which word you will use.
example in bahasa:
'bisa', could means poison in bahasa and high probability pair with snake or bite
'bisa', could means can do something in bahasa, high probabilty pairing with verbs words or expression of willing to do something (verbs)
so if the tokenize result pairing with snake or bite, you search the similar meaning in answer by checking snake and poison in english. and search in english database, and you will found venom always pair with snake(have similar means with toxin / poison).
another group can do by words type (nouns, verbs, adjective, etc).
bisa == poison (noun)
bisa == can (verbs).
that's it. after have the calculation, you don't need the data base, you only need word matching data.
so the calcultaion that you can do by checking online data (ex: wikipedia) or download it or use bible/book file or any other database that contains lots of sentence.

Efficient replacement of occurrences of a list of words

I need to censor all occurrences of a list of words with *'s. I have about 400 words in the list and it's going to get hit with a lot of traffic, so I want to make it very efficient. What's an efficient algorithm/data structure to do this in? Preferably something already in Python.
Examples:
"piss off" => "**** off"
"hello" => "hello"
"go to hell" => "go to ****"

A case-insensitive trie-backed set implementation might fit the bill. For each word, you'll only process a minimum of characters. For example, you would only need to process the first letter of the word 'zoo' to know the word is not present in your list (assuming you have no 'z' expletives).
This is something that is not packaged with python, however. You may observe better performance from a simple dictionary solution since it's implemented in C.

(1) Let P be the set of phrases to censor.
(2) Precompute H = {h(w) | p in P, w is a word in p}, where h is a sensible hash function.
(3) For each word v that is input, test whether h(v) in H.
(4) If h(v) not in H, emit v.
(5) If h(v) in H, back off to any naive method that will check whether v and the words following form a phrase in P.
Step (5) is not a problem since we assume that P is (very) small compared to the quantity of input. Step (3) is an O(1) operation.

like cheeken has mentioned, a Trie may be the thing you need, and actually, you should use Aho–Corasick string matching algorithm. Something more than a trie.
For every string, say S you need to process, the time complexity is approximately O(len(S)). I mean, Linear
And you need to build the automaton initially, it's time complexity is O(sigma(len(words))), and space complexity is about(less always) O(52*sigma(len(words))) here 52 means the size of the alphabet(i take it as ['a'..'z', 'A'..'Z']). And you need to do this just for once(or every time the system launches).

You might want to time a regexp based solution against others. I have used similar regexp based substitution of one to three thousand words on a text to change phrases into links before, but I am not serving those pages to many people.
I take the set of words (it could be phrases), and form a regular expression out of them that will match their occurrence as a complete word in the text because of the '\b'.
If you have a dictionary mapping words to their sanitized version then you could use that. I just swap every odd letter with '*' for convenience here.
The sanitizer function just returns the sanitized version of any matched swear word and is used in the regular expression substitution call on the text to return a sanitized version.
import re
swearwords = set("Holy Cow".split())
swear = re.compile(r'\b(%s)\b' % '|'.join(sorted(swearwords, key=lambda w: (-len(w), w))))
sanitized = {sw:''.join((ch if not i % 2 else '*' for i,ch in enumerate(sw))) for sw in swearwords}
def sanitizer(matchobj):
return sanitized.get(matchobj.group(1), '????')
txt = 'twat prick Holy Cow ... hell hello shitter bonk'
swear.sub(sanitizer, txt)
# Out[1]: 'twat prick H*l* C*w ... hell hello shitter bonk'
You might want to use re.subn and the count argument to limit the number of substitutions done and just reject the whole text if it has too many profanities:
maxswear = 2
newtxt, scount = swear.subn(sanitizer, txt, count=maxswear)
if scount >= maxswear: newtxt = 'Ouch my ears hurt. Please tone it down'
print(newtxt)
# 'Ouch my ears hurt. Please tone it down'

If performance is what you want I would suggest:
Get a sample of the input
Calculate the average amount of censored words per line
Define a max number of words to filter per line (3 for example)
Calcule what censored words have the most hits in the sample
Write a function that given the censored words, will generate a
python file with IF statements to check each words, putting the 'most
hits' words first, since you just want to match whole words it will
be fairly simple
Once you hit the max number per line, exit the function
I know this is not nice and I'm only suggesting this approach because of the high traffic scenario, doing a loop of each word in your list will have a huge negative impact on performance.
Hope that help or at least give you some out of the box idea on how to tackle the problem.

algorithm for testing mutliple substrings in multiple strings

I have several million strings, X, each with less than 20 or so words. I also have a list of several thousand candidate substrings C. for each x in X, I want to see if there are any strings in C that are contained in x. Right now I am using a naive double for loop, but it's been a while and it hasn't finished yet...Any suggestions? I'm using python if any one knows of a nice implementation, but links for any language or general algorithms would be nice too.

Encode one of your sets of strings as a trie (I recommend the bigger set). Lookup time should be faster than an imperfect hash and you will save some memory too.

It's gonna be a long while. You have to check every one of those several million strings against every one of those several thousand candidate substrings, meaning that you will be doing (several million * several thousand) string comparisons. Yeah, that will take a while.
If this is something that you're only going to do once or infrequently, I would suggest using fgrep. If this is something that you're going to do often, then you want to look into implementing something like the Aho-Corasick string matching algorithm.

If your x in X only contains words, and you only want to match words you could do the following:
Insert your keywords into a set, that makes the access log(n), and then check for every word in x if it is contained in that set.
like:
keywords = set(['bla', 'fubar'])
for w in [x.split(' ') for x in X]:
if w in keywords:
pass # do what you need to do
A good alternative would be to use googles re2 library, that uses super nice automata theory to produce efficient matchers. (http://code.google.com/p/re2/)
EDIT: Be sure you use proper buffering and something in a compiled language, that makes it a lot faster. If its less than a couple gigabytes, it should work with python too.

you could try to use regex
subs=re.compile('|'.join(C))
for x in X:
if subs.search(x):
print 'found'

Have a look at http://en.wikipedia.org/wiki/Aho-Corasick. You can build a pattern-matcher for a set of fixed strings in time linear in the total size of the strings, then search in text, or multiple sections of text, in time linear in the length of the text + the number of matches found.
Another fast exact pattern matcher is http://en.wikipedia.org/wiki/Rabin-Karp_string_search_algorithm

Search many expressions in many documents using Python

I often have to search many words (1000+) in many documents (million+). I need position of matched word (if matched).
So slow pseudo version of code is
for text in documents:
for word in words:
position = search(word, text)
if position:
print word, position
Is there any fast Python module for doing this? Or should I implement something myself?

For fast exact-text, multi-keyword search, try acora - http://pypi.python.org/pypi/acora/1.4
If you want a few extras - result relevancy, near-matches, word-rooting etc, Whoosh might be better - http://pypi.python.org/pypi/Whoosh/1.4.1
I don't know how well either scales to millions of docs, but it wouldn't take long to find out!

What's wrong with grep?
So you have to use python? How about:
import subprocess
subprocess.Popen('grep <pattern> <file>')
which is insane. But hey! You are using python ;-)

Assuming documents is a list of strings, you can use text.index(word) to find the first occurrence and text.count(word) to find the total number of occurrences. Your pseudocode seems to assume words will only occur once, so text.count(word) may be unnecessary.