1. control 4 Day /01/14
LING 3820 & 6820
Natural Language Processing
Harry Howard
Tulane University

2. Course organization http://www.tulane.edu/~howard/LING3820/
The syllabus is under construction.
Chapter numbering
3.7. How to deal with non-English characters
4.5. How to create a pattern with Unicode characters
6. Control
NLP, Prof. Howard, Tulane University
29-Sept-2014

3. Review of control
NLP, Prof. Howard, Tulane University
29-Sept-2014

4. Conditional expressions
>>> if True:
... do something
...
... elif True:
... else:
NLP, Prof. Howard, Tulane University
29-Sept-2014

5. For loop & list conmprehension
>>> for item in container:
... do something to item
...
>>> newList = []
... newList.append(item)
>>> newList = [item for item in container]
NLP, Prof. Howard, Tulane University
29-Sept-2014

6. Add a condition >>> newList = []
>>> for item in container:
... if condition:
... newList.append(item)
...
>>> newList = [item for item in container if condition]
NLP, Prof. Howard, Tulane University
29-Sept-2014

7. Open Spyder
NLP, Prof. Howard, Tulane University
29-Sept-2014

8. 6.3.4. How to check a condition in a loop
NLP, Prof. Howard, Tulane University
29-Sept-2014

9. Chained conditions in a loop
>>> greeting = 'Yo!' >>> caseList = [] >>> for char in greeting: ... if char.islower(): ... caseList.append('yes') ... elif char.isupper(): ... caseList.append('no') ... else: ... caseList.append('whoops!') ... >>> caseList ['no', 'yes', 'whoops!']
NLP, Prof. Howard, Tulane University
29-Sept-2014

10. A chained conditional list comprehension
However there is no list comprehension that is exactly analogous to a chained conditional, since elif is not allowed in them.
A list comprehension only allows if -- else, so the elif has to be decomposed into else -- if.
Here is what it looks like in a loop:
NLP, Prof. Howard, Tulane University
29-Sept-2014

11. Example >>> caseList = [] >>> for char in greeting:
... if char.islower():
... caseList.append('yes')
... else:
... if char.isupper():
caseList.append('no')
... else:
caseList.append('whoops!')
...
>>> caseList
['no', 'yes', 'whoops!']
>> caseList = ['yes' if char.islower() else 'no' if char.isupper() else 'whoops!' for char in greeting]
NLP, Prof. Howard, Tulane University
29-Sept-2014

12. 6.3.5. How to transform items within a loop
The argument of append() takes any type that can be an element of a list, such as strings or integers, so it can hold the result of a method:
>>> upperList = []
>>> for char in greeting:
... upperList.append(char.upper())
...
>>> upperList ['Y', 'O', '!']
>>> lenList = []
>>> for word in fruit:
... lenList.append(len(word))
>>> lenList
[5, 6, 5, 4, 10]
NLP, Prof. Howard, Tulane University
29-Sept-2014

13. >>> upperList = [char.upper() for char in greeting]
A list comprehension can perform the same change by applying it to the first mention of the item:
>>> upperList = [char.upper() for char in greeting]
>>> upperList
['Y', 'O', '!']
>>> lenList = [len(word) for word in fruit]
>>> lenList
[5, 6, 5, 4, 10]
NLP, Prof. Howard, Tulane University
29-Sept-2014

14. Next time Finish control NLP, Prof. Howard, Tulane University
29-Sept-2014