LING/C SC/PSYC 438/538. Lecture 10 Sandiway Fong

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1 LING/C SC/PSYC 438/538 Lecture 10 Sandiway Fong

2 Administrivia Homework 4 Perl regex Python re import re slightly complicated string handling: use raw g/3/library/re.html

3 Regular Expressions to the rescue

$Regular Expressions from Hell Email validation: RFC 5322: (?:[a-z0-9!#$%&'*+/=?^_`{ }~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{ }~- ]+)* "(?$

4 Regular Expressions from Hell validation: RFC 5322: (?:[a-z0-9!#$%&'*+/=?^_`{ }~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{ }~- ]+)* "(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f] \\[\x01- \[(?:(?:(2(5[0-5] [0-4][0-9]) 1[0-9][0-9] [1-9]?[0-9]))\.){3}(?:(2(5[0-5] [0-4][0-9]) 1[0-9][0-9] [1-9]?[0-9]) [a-z0-9- ]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f] \\[\x01- \x09\x0b\x0c\x0e-\x7f])+)\])

5 File I/O Summary Common: open filehandle close Perl: <filehandle> print filehandle String Python: (concept comes from the underlying OS) (context: reads a line or the whole file) (methods).readline().readlines().write(string) (no newline) print(*objects, sep=' ', end='\n', file=sys.stdout, flush=false) (function)

6 Homework 4 File: population.txt Contents: rank name continent population (2016) population (2017) fields are separated by a tab (\t) Source: Wikipedia

7 Homework 4: Question 1 Using Perl read the file create hash table(s) indexed by country name containing the following information: continent/2016 population/2017 population 1. Compute and print the country that decreased in population. 2. Compute and print the country with the smallest positive increase in population. 3. Print a table of countries in Asia and 2016 population ranked by 2016 population 4. Print a table of countries in Africa and 2016 population ranked inversely by 2016 population Hints: read about split read about tr: $num =~ tr/,//d deletes the pesky commas in $num revisit sort parameters: if you need to trim whitespace from the ends: $line =~ s/^\s+ \s+$//g; for nicely-formatted lists, read about printf FORMAT

8 Homework 4: Question 2 Review Do the same exercise in Python3 using a dictionary or dictionaries These may prove useful: str.strip() str.replace() str.split() sys.argv int()

9 Homework 4: Question 3 In Your Opinion: which code is simpler?

10 Homework 4 Usual submission rule: ONE PDF file Submit code/run/comments subject heading: 438/538 Homework 4 Your Name Due date by midnight of next Monday (review in class on Tuesday)

11 regex Read textbook chapter 2: section 1 on Regular Expressions

12 Perl regex Read up on the syntax of Perl regular expressions Online tutorials

13 Perl regex Perl regex matching: $a =~ /foo/ (/ / contains a regex) can use in a conditional: e.g. if ($a =~ /foo/) evaluates to true/false depending on what s in $a can also use as a statement: e.g. $a =~ /foo/; variable $& contains the match Perl regex match and substitute: $a =~ s/foo/bar/ s/ match / substitute / contains two expressions will modify $a by looking for a single occurrence of match and replacing that with substitute s/ match / substitute /g global substitution

14 Perl regex Most useful with the code template for reading in a file line-by-line: open($txtfile, $ARGV[0]) or die "$ARGV[0] not found!\n"; while ($line = <$txtfile>) { do RE stuff with $line } close($txtfile)

15 Chapter 2: JM character class: Perl lingo

16 Chapter 2: JM range: in ASCII table backslash lowercase letter for class Uppercase variant for all but class

17 Chapter 2: JM

18 Chapter 2: JM Sheeptalk

$Perl regex \S+ing\b \s is a whitespace, so \S is a nonwhitespace + is$

19 Perl regex \S+ing\b \s is a whitespace, so \S is a nonwhitespace + is repetition (1 or more) \b is a word boundary, (words are made up of \w characters)

$regex \b$ $or \b{wb}$

20 Perl regex \b or \b{wb} global variables

21 Perl regex: Unicode and \b \b \b{wb} Note: global match in while-loop

$Perl regex: Unicode and \w \w is [0-9A-Za-z_] Definition is expanded for Unicode: use utf8; use open qw(:std :utf8); Pragma https://perldoc.perl.org/open.$

22 Perl regex: Unicode and \w \w is [0-9A-Za-z_] Definition is expanded for Unicode: use utf8; use open qw(:std :utf8); Pragma my $str = "school école École šola trường!क ल škole โรงเร = ($str =~ /(\w+)/g); foreach $word (@words) { print "$word\n" } list context

23 Chapter 2: JM

24 Chapter 2: JM Precedence of operators Example: Column 1 Column 2 Column 3 /Column [0-9]+ */ /(Column [0-9]+ *)*/ /house(cat(s ) )/ space ( = disjunction;? = optional) Perl: in a regular expression the pattern matched by within the pair of parentheses is stored in global variables $1 (and $2 and so on) Precedence Hierarchy:

Perl regex http://perldoc.perl.org/perlretut.

25 Perl regex A shortcut: list context for matching returns 1 (true) or "" (empty if false) returns a list

LING/C SC/PSYC 438/538. Lecture 6 Sandiway Fong

LING/C SC/PSYC 438/538. Lecture 6 Sandiway Fong LING/C SC/PSYC 438/538 Lecture 6 Sandiway Fong Today s Topic Homework 2 out today due next Thursday by midnight submit one file only (preferably PDF) Subject line: Your Name 538/438 Homework 2 Perl Recap