Unicode & controlDay 13 - 9/24/14LING 3820 & 6820

Natural Language Processing

Harry Howard

Tulane University

Course organization

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

The syllabus is under construction.

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

Review of Unicode

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ASCII characters

  0 1 2 3 4 5 6 7 8 9 A B C D E F

0 – – – – – – – – – – – – – – – –

1 – – – – – – – – – – – – – – – –

2   ! “ # $ % & ‘ ( ) * + , - . /

3 0 1 2 3 4 5 6 7 8 9 : ; < = > ?

4 @ A B C D E F G H I J K L M N O

5 P Q R S T U V W X Y Z [ \ ] ^ _

6 ` a b c d e f g h i j k l m n o

7 p q r s t u v w x y z { | } ~ –

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6.2.1. Character encoding in Python

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Open Spyder

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6. Non-English characters: one code to rule them all

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6.2.2. What happens when you type a non-ASCII character into a Python console?

1. >>> import sys 2. >>> sys.getdefaultencoding()

1. >>> special = 'ó' 2. >>> special 3. '\xc3\xb3' 4. >>> print special ó

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6.2.3. How to translate into and out of Unicode with decode() and encode()1. >>> S1 = 'ca\xc3\xb1\xc3\xb3n' 2. >>> uS1 = S1.decode('utf8') 3. >>> uS1 4. u'ca\xf1\xf3n'5. >>> len(uS1) 6. 5 7. >>> utf8S1 = uS1.encode('utf8')8. >>> print utf8S1 9. cañón

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6.2.4.1. How to turn on non-ASCII character matching with re.UNICODE1. >>> S1 = 'ca\xc3\xb1\xc3\xb3n' # same as before

2. >>> uS1 = S1.decode('utf8')

3. >>> uS1

4. u'ca\xf1\xf3n'

5. >>> import re

6. >>> lS1 = re.findall(r'\w{5}', uS1, re.U)

7. >>> lS1

8. [u'ca\xf1\xf3n']

9. >>> eS1 = ''.join(lS1)

10. >>> eS1

11. u'ca\xf1\xf3n'

12. >>> utf8S1 = eS1.encode('utf8')

13. >>> utf8S1

14. 'ca\xc3\xb1\xc3\xb3n'

15. >>> print

16. cañón

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6.2.5. How to translate between Unicode strings and numbers with ord() and unichar()1. >>> 'ó' 2. '\xc3\xb3' 3. >>> 'ó'.decode('utf8') 4. u'\xf3' 5. >>> ord(u'\xf3') 6. 243 7. >>> unichr(243) 8. u'\xf3' 9. test = unichr(243).encode('utf8')10. >>> print test 11. ó

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I am going to fold the Unicode chapter into §1 & §2 and move the next chapter (§8) up a notch, so the chapter numbering will change.

Chapter numbering

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Up to now, your short programs are entirely dependent on you for making decisions. This is fine for pieces of text that fit on a single line, but is clearly insufficient for texts that run to hundreds of lines in length. You will want Python to make decisions for you. How to tell Python to do so is the topic of this chapter, and falls under the rubric of control.

8. Control

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The first step in making a decision is to distinguish those cases in which the decision applies from those in which it does not. In computer science, this is usually known as a condition.

8.1. Conditions

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8.1.1. How to check for the presence of an item with in Perhaps the simplest condition in text processing is whether an item is present or not. Python handles this in a way that looks a lot like English:

1. >>> greeting = 'Yo!' 2. >>> 'Y' in greeting3. >>> 'o' in greeting4. >>> '!' in greeting5. >>> 'o!' in greeting6. >>> 'Yo!' in greeting7. >>> 'Y!' in greeting8. >>> 'n' in greeting9. >>> '?' in greeting10.>>> '' in greeting

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in & lists

Lists behave exactly like strings, with the proviso that the string being asked about match a string in the list exactly:

1. >>> fruit = ['apple', 'cherry', 'mango', 'pear', 'watermelon']

2. >>> 'apple' in fruit

3. >>> 'peach' in fruit

4. >>> 'app' in fruit

5. >>> '' in fruit

6. >>> [] in fruit

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Python can understand sequences of in conditions

1. >>> 'app' in 'apple' in fruit2. # 'app' in 'apple' > True 3. # 'apple' in lst > True 4. >>> 'aple' in 'apple' in fruit5. >>> 'pea' in 'peach' in fruit

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8.1.2. How to check for the absence of an item with not in1. >>> not 'n' in greeting2. >>> 'n' not in greeting3. >>> 'Y' not in greeting4. >>> 'Y!' not in greeting5. >>> 'Yo' not in greeting6. >>> '' not in greeting7. >>> 'apple' not in fruit8. >>> 'peach' not in fruit9. >>> 'app' not in fruit10. >>> '' not in fruit11. >>> 'pee' not in 'peach' not in fruit12. >>> 'pea' not in 'peach' not in fruit13. >>> 'pea' not in 'apple' not in fruit

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More on control

Next time

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