Computation with strings 3Day 4 - 9/03/14LING 3820 & 6820Natural Language ProcessingHarry HowardTulane University

Course organization

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http://www.tulane.edu/~howard/LING3820/

The syllabus is under construction. http://www.tulane.edu/~howard/CompCu

ltEN/ Is there anyone here that wasn't here on

Wednesday? Take pictures.

Measure heads

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NLP, Prof. Howard, Tulane University

Computer hygiene You must turn

your computer off every now and then, so that it can clean itself.

By the same token, you should close applications every now and then.

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NLP, Prof. Howard, Tulane University

Go over homework

Review

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NLP, Prof. Howard, Tulane University

3.5. Practice1. What types are output by len(), sort(), set()?2. Here are two real life strings to work with:>>> mail = howard@tulane.edu>>> url = http://www.tulane.edu/~howard/CompCultEN/

a. How would you strip out the user name and the server name from my email address?

b. Internet addresses start with the transfer protocol that the site uses. For web pages, this is usually the hypertext transfer protocol, http. How would you strip this information out to leave just the address of the book?

c. Following up on (b), how would you extract just Tulane’s server address?

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3.5. Practice, cont3. Write the code to perform the changes given

below on these two strings:>>> S = 'ABCDEFGH'>>> s = 'abcdefgh'

a. Make the first 3 characters of S lowercase.b. Make the last 4 characters of s uppercase.c. Create a string from the first 4 characters of S and

the last 4 characters of s and then switch its case.d. Join both strings and find every even character.e. Join both strings and reverse the order of the

characters.f. Retrieve the index of ‘E’ and ‘h’.

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3.5. Practice, cont4. What is the longest sequence of operators that you can

make?5. Show which of len(), sort(), and set() takes the most time

to process.6. Line 2 from the previous subsection has the expression

L[2:6].capitalize().upper(). Show whether it is faster for Python to process this as it is, or broken into its parts as in:>>> A = L[2:6]>>> B = A.capitalize()>>> C = B.upper()

7. Recall the discussion of the default precedence of * and + in §3.1.1. Perhaps * comes first because it is quicker to process than +. Test this hypothesis by writing a function for either combination of * and + and time them to see which runs faster.

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Finish homework & §3

Next time

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