1. LING/C SC/PSYC 438/538
Lecture 7
Sandiway Fong

2. Administrivia Homework 5 graded Terminal log from last time
Homework 5 review
Quick Homework 6
(Heads Up: Homework 7 coming on Thursday)
Perl Hashes and Python dicts

3. Terminal log from last time
Desktop$ perl -le = qw-a aa aaa A AA AAA ( ) { }-; print a aa aaa A AA AAA ( ) { } Desktop$ perl -le = qw-a aa aaa A AA AAA ( ) { = print ( ) A AA AAA a aa aaa { } Desktop$ perl -le = qw-a aa aaa A AA AAA ( ) { = sort {\$a cmp print Desktop$ perl -le = qw ( ) { = sort {\$a <=> print 0 ( ) { }

4. Terminal log from last time
Desktop$ perl -le = qw-a b c A B C-; use feature = sort {fc(\$a) cmp print a A b B c C Desktop$ perl -le = qw-A B C a b c-; use feature = sort {fc(\$a) cmp print A a B b C c Desktop$ perl -le = qw a = print A a Desktop$ perl -le = (0, 5, 3, 2, 1, 99, 'a', = print Desktop$

5. Homework 5 Review Perl Resources:
sub
substr
length
if-then-else

6. Homework 5 Review
palindrome.py
Desktop$ python3 pallindrome.py dad True Desktop$ python3 pallindrome.py dada False Desktop$ python3 pallindrome.py racecar Desktop$

7. Homework 5 Review Let's write the Perl program! length($word)
substr($word, -1)
substr EXPR,OFFSET,LENGTH
substr($word, 0, 1)
substr($word, 1, -1) or
substr($word, 1, length($word)-2)

8. Homework 5 Review (Bonus)
One student tried '好不好' (good-NOT-good => OK?), but the palindrome code didn't work.
Chinese tag questions:
对不对 true (or not)? 有没有 exists (or not)? 是不是 yes (or no)?
Perl pre-dates Unicode:
and Unicode support is not turned on by default for backwards compatibility.
perl -C [number/list]
A elements are expected to be strings encoded in UTF-8.
O STDOUT will be in UTF-8.
I STDIN is assumed to be in UTF-8.
S I + O + E.

9. Quick Homework 6 Due tomorrow night: reviewed on Thursday
Question 1: what's the difference between a) and b)?
= 4 x 4;
= (4) x 4;
read
Question 2: what does split do here for a) vs. b)?
= split " ", 'this is a sentence.';
= split //, 'this is a sentence.';
Due tomorrow night: reviewed on Thursday

10. Perl Hashes
dict in Python
Note:
Perl […]
Perl hash: % {…}

11. no quotes needed for strings
Perl Hashes
Notes on arrays and hashes
arrays are indexed using integers
hashes are like arrays with user-defined indexing
(aka associative array or hash table or dictionary (Python))
initialization
(use list notation (or shortcut): round brackets and commas)
@a = ("zero", "one", "two", "three", "four");
%h = ("zero", 0, "one", 1, "two", 2, "three", 3, "four", 4); (key/value pairs)
access to individual elements
(square brackets vs. curly braces)
$a[1] “one”
$h{zero} 0
Shortcut:
no quotes needed for strings
'zero' "zero"

12. Perl Hashes Notes on arrays and hashes output
zeroonetwothreefour
print zero one two three four
print %h three3one1zero0two2four4 (note: different order)
print "%h" %h (literal, no interpolation done)

13. More on Hash tables
Looping over arrays:
Output:

14. More on Hash tables Exists: Unique key constraint:
exists $fruitColor{apple}
exists $fruitColor{orange}

15. Dictionaries (dict)
Lists and tuples are indexed by whole numbers (from 0)
Dictionaries are indexed by a key (usually a string) and return some value associated with the key
Note: use of curly braces
Dictionaries are not ordered (like sets) – see next slide
Methods keys(), values(), items()
Refer to key + value as an item: encoded as a tuple

16. Dictionaries (dict)

17. Python dict
Dictionary order preservation depends on the version of Python used …
Python 3.6

18. Python dict
list comprehension

19. Python dict How to print the contents of a dictionary?
Use a for-loop and method items(): k,v is a tuple

20. Python dict All values are lists Advantage: simplifies the code
Trade-off
Values are lists or a string
Advantage: simpler-looking dict

21. Python dict Works too! Less transparent: relies on a
Python-particular quirk …

22. Python dict
function zip() pairs up elements from two lists into an iterable

23. Python dict
function zip() doesn't always work quite the same …

24. Python list ranges Perl has a range operator: ..
less powerful in some ways, more powerful in others