1. LING 388: Computers and Language
Lecture 15

2. Administrivia
Reminder Homework 7 due Friday (or Saturday) night by midnight
Printout of last lecture's terminal available as lecture14.txt

4. Python regex
Methods:
Key: RE = regex raw string, String = where to search
import re
re.match(RE, String) matching must start from start of String
re.search(RE, String) searches anywhere in String
re.findall(RE, String)
re.finditer(RE, String) use with loop for m in re.finditer()
re.sub(RE, SUB, String) SUB = regex raw string to substitute for RE

5. Substitution examples
Using re.sub(RE, SUB, String)
Example:
import re
text =  "Google is a tech giant. Google is the most valuable company in the world."
re.sub(r"Google","Microsoft",text)
'Microsoft is a tech giant. Microsoft is the most valuable company in the world.'
text
'Google is a tech giant. Google is the most valuable company in the world.'
re.sub(r"Google","Microsoft",text,1)
'Microsoft is a tech giant. Google is the most valuable company in the world.'

6. Substitution examples
Using re.sub(RE, SUB, String)
Substitution using .sub() with backreferences and grouping:
Suppose we want to change section{one} into subsection{one}
[^}] means any character but }
(..) capturing group

7. Running Python on the command line in Windows

8. More Python regex practice
Download wordlist.py (Brown Corpus words) to your computer
Put it on the same directory as your Python
Then run the following:

9. Python regex practice Exercise 1: Exercise 2: Exercise 3:
produce a list of all the words in wordlist that having two a's in a row
aa = [word for word in wordlist if re.search('aa',word)]
len(aa)
Exercise 2:
are there more words with two b's in a row?
Exercise 3:
words with two p's or b's or d's in a row – which is the most frequent?

10. Python regex practice Exercise 4: Exercise 5: Exercise 6: Exercise 7:
find a word with both bb and dd in it
Exercise 5:
are there any words with pp and dd?
Exercise 6:
find words ending in zac. How many are there?
Recall: meta-character for the end of line anchor is $
Exercise 7:
find words beginning in anti. How many are there?
Hint: some cases may begin with a capital letter

11. Python regex practice Look for words with prefix "pre"
Are all of them correct? (cf. pretend)
Devise a search that looks for words beginning with 'pre' but also contains the rest of the word as a word in the Brown corpus