Natural language processing (Python)


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It's a brief overview of Natural Language Processing using Python module NLTK.The codes for demonstration can be found from the github link given in the references slide.

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Natural language processing (Python)

  1. 1. Natural Language Processing Using Python Presented by:- Sumit Kumar Raj 1DS09IS082ISE,DSCE-2013
  2. 2. Table of Contents • Introduction • History • Methods in NLP • Natural Language Toolkit • Sample Codes • Feeling Lonely ? • Building a Spam Filter • Applications • ReferencesISE,DSCE-2013 1
  3. 3. What is Natural Language Processing ? •Computer aided text analysis of human language. •The goal is to enable machines to understand human language and extract meaning from text. •It is a field of study which falls under the category of machine learning and more specifically computational linguistics.ISE,DSCE-2013 2
  4. 4. History • 1948- 1st NLP application – dictionary look-up system – developed at Birkbeck College, London • l 1949- American interest –WWII code breaker Warren Weaver – He viewed German as English in code. • 1966- Over-promised under-delivered – Machine Translation worked only word by word l – NLP brought the first hostility of research funding l – NLP gave AI a bad name before AI had a name.ISE,DSCE-2013 3
  5. 5. Natural language processing is heavily used throughout all web technologies Search engines Consumer behavior analysis Site recommendations Sentiment analysis Spam filtering Automated customer Knowledge bases and support systems expert systemsISE,DSCE-2013 4
  6. 6. Context Little sister: What’s your name? Me: Uhh….Sumit..? Sister: Can you spell it? Me: yes. S-U-M-I-T…..ISE,DSCE-2013 5
  7. 7. Sister: WRONG! It’s spelled “I- T”ISE,DSCE-2013 6
  8. 8. Ambiguity “I shot the man with ice cream.“ - A man with ice cream was shot - A man had ice cream shot at himISE,DSCE-2013 7
  9. 9. Methods :- 1) POS Tagging :- •In corpus linguistics, Parts-of-speech tagging also called grammatical tagging or word-category disambiguation. •It is the process of marking up a word in a text corres- ponding to a particular POS. •POS tagging is harder than just having a list of words and their parts of speech. •Consider the example: l The sailor dogs the barmaid.ISE,DSCE-2013 8
  10. 10. 2) Parsing :- •In context of NLP, parsing may be defined as the process of assigning structural descriptions to sequences of words in a natural language. Applications of parsing include simple phrase finding, eg. for proper name recognition Full semantic analysis of text, e.g. information extraction or machine translationISE,DSCE-2013 9
  11. 11. 3) Speech Recognition:- • It is concerned with the mapping a continuous speech signal into a sequence of recognized words. • Problem is variation in pronunciation, homonyms. • In sentence “the boy eats”, a bi-gram model sufficient to model the relationship b/w boy and eats. “The boy on the hill by the lake in our town…eats” • Bi-gram and Trigram have proven extremely effective in obvious dependencies.ISE,DSCE-2013 10
  12. 12. 4) Machine Translation:- • It involves translating text from one NL to another. • Approaches:- -simple word substitution,with some changes in ordering to account for grammatical differences -translate the source language into underlying meaning representation or interlinguaISE,DSCE-2013 11
  13. 13. 5) Stemming:- • In linguistic morphology and information retrieval, stemming is the process for reducing inflected words to their stem. • The stem need not be identical to the morphological root of the word. • Many search engines treat words with same stem as synonyms as a kind of query broadening, a process called conflation.ISE,DSCE-2013 12
  14. 14. Natural Language Toolkit • NLTK is a leading platform for building Python program to work with human language data. • Provides a suite of text processing libraries for classification, tokenization, stemming, tagging, parsing, and semantic reasoning. • Currently only available for Python 2.5 – 2.6 • `easy_install nltk • Prerequisites – NumPy – SciPyISE,DSCE-2013 13
  15. 15. Let’s dive into some code!ISE,DSCE-2013 14
  16. 16. Part of Speech Taggingfrom nltk import pos_tag,word_tokenizesentence1 = this is a demo that will show you howto detects parts of speech with little effortusing NLTK!tokenized_sent = word_tokenize(sentence1)print pos_tag(tokenized_sent)[(this, DT), (is, VBZ), (a, DT), (demo, NN), (that, WDT),(will, MD), (show, VB), (you, PRP), (how, WRB), (to, TO),(detects, NNS), (parts, NNS), (of, IN), (speech, NN), (with,IN), (little, JJ), (effort, NN), (using, VBG), (NLTK, NNP),(!,.)]ISE,DSCE-2013 15
  17. 17. Fun things to TryISE,DSCE-2013 16
  18. 18. Feeling lonely? Eliza is there to talk to you all day! What human could ever do that for you?? from import eliza eliza.eliza_chat() ……starts the chatbot Therapist --------- Talk to the program by typing in plain English, using normal upper- and lower-case letters and punctuation. Enter "quit" when done. ============================================================ ============ Hello. How are you feeling today?ISE,DSCE-2013 17
  19. 19. Let’s build something even coolerISE,DSCE-2013 18
  20. 20. Lets write a Spam filter! A program that analyzes legitimate emails “Ham” as well as “Spam” and learns the features that are associated with each. Once trained, we should be able to run this program on incoming mail and have it reliably label each one with the appropriate category.ISE,DSCE-2013 19
  21. 21. “” (continued) 1. Extract one of the archives from the site into your working directory. 2. Create a python script, lets call it “”. Your working directory should contain the “spambot” script and the 3. folders “spam” and “ham”.from nltk import word_tokenize,WordNetLemmatizer,NaiveBayesClassifier,classify,MaxentClassifierfrom nltk.corpus import stopwordsimport randomISE,DSCE-2013 20
  22. 22. “” (continued)label each item with the appropriate label and store them as a list of tuplesmixedemails = ([(email,spam) for email in spamtexts]mixedemails += [(email,ham) for email in hamtexts])From this list of random but labeled emails, we will defined a “featureextractor” which outputs a feature set that our program can use to statisticallycompare spam and ham.random.shuffle(mixedemails) lets give them a nice shuffleISE,DSCE-2013 21
  23. 23. “” (continued)def email_features(sent): features = {} wordtokens = [wordlemmatizer.lemmatize(word.lower()) forword in word_tokenize(sent)] Normalize words for word in wordtokens: if word not in commonwords: features[word] = True return features If the word is not a stop-word then lets consider it a “feature”featuresets = [(email_features(n), g) for (n,g) in mixedemails]ISE,DSCE-2013
  24. 24. “” (continued)While True: featset = email_features(raw_input("Enter text to classify: ")) print classifier.classify(featset)We can now directly input new email and have it classified as either Spam orHamISE,DSCE-2013 23
  25. 25. Applications :- • Conversion from natural language to computer language and vice-versa. • Translation from one human language to another. • Automatic checking for grammar and writing techniques. • Spam filtering • Sentiment AnalysisISE,DSCE-2013 24
  26. 26. Conclusion:- NLP takes a very important role in new machine human interfaces. When we look at Some of the products based on technologies with NLP we can see that they are very advanced but very useful. But there are many limitations, For example language we speak is highly ambiguous. This makes it very difficult to understand and analyze. Also with so many languages spoken all over the world it is very difficult to design a system that is 100% accurate. These problems get more complicated when we think of different people speaking the same language with different styles. Intelligent systems are being experimented right now. We will be able to see improved applications of NLP in the near future.ISE,DSCE-2013 25
  27. 27. References :-•• An overview of Empirical Natural Language Processing by Eric Brill and Raymond J. Mooney• Investigating classification for natural language processing tasks by Ben W. Medlock, University of Cambridge• Natural Language Processing and Machine Learning using Python by Shankar Ambady.•• Codes from :,DSCE-2013 26
  28. 28. Any Questions ???ISE,DSCE-2013 27
  29. 29. Thank You... Reach me @: 9590 285 524ISE,DSCE-2013