Notes for CSC 162, 20 April 2010 ff
(not in the text)

Project 6 due Friday 30 Apr., noon

PLEASE FILL OUT ON-LINE COURSE EVALUATION

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Python as a scripting ("glue") language

"force kill" example

    import sys, os, re, time
    if len(sys.argv) != 2:
        sys.stderr.write('usage: ' + sys.argv[0] + ' pattern\n')
        sys.exit(1)

    PS = os.popen("/bin/ps -w -w -x -o'pid,command'")
        # -w -w : unlimited width output
        # -x : don't require a controlling terminal
        # -o'pid,command' : output fields
    line = PS.readline()                # discard header line
    line = PS.readline().rstrip()       # prime pump
    while line != "":
        proc = int(re.search('\S+', line).group())
            # RE matches any string of non-whitespace characters
            # group() returns the whole match
        if re.search(sys.argv[1], line) and proc != os.getpid(): 
            print line + '? ',
            answer = sys.stdin.readline()
            while not re.search('^[yn]', answer, re.I):
                # .I flag : ignore case
                print '? ',             # trailing comma inhibits newline
                answer = sys.stdin.readline()
            if re.search('^y', answer, re.I):
                os.kill(proc, 9)
                  time.sleep(1)
                try:                    # expect exception if process
                    os.kill(proc, 0)    # no longer exists
                    sys.stderr.write("unsuccessful; sorry\n"); sys.exit(1)
                except: pass        # do nothing
            sys.stdout.write('')    # inhibit prepended blank on next print
        line = PS.readline().rstrip()

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Web scripting
    CGI
    server-side
    client-side

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CGI scripting in Python

http://localhost/cgi-bin/status.py
    (file /Library/WebServer/CGI-Executables/status.py)

http://localhost/~scott/add.html
    (file /Users/scott/Sites/add.html;
    calls /Library/WebServer/CGI-Executables/add.py)

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server-side scripting in PHP

http://localhost/~scott/add2.html
    (file /Users/scott/Sites/add2.html)
http://localhost/~scott/add.php
    (file /Users/scott/Sites/add.php)

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client-side scripting in JavaScript

http://localhost/~scott/js_adder.html
    (file /Users/scott/Sites/js_adder.html)

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Intro to Java

concept of compilation
    efficiency
    early error detection
    JIT compilation
    javac, java

static typing
    declarations
        built-ins
            can't be target of a reference, or element of a container
        classes
            set of fields, methods statically known
    parameter passing
        quite similar to Python
        built-ins (ints, doubles, chars, Booleans) passed by value
        objects (including arrays) passed by reference

everything embedded in a class
    public, private
    static
free-format, with curly braces and semicolons

hello, world:

    class hello {
        public static void main(String[] args) {
            System.out.println("hello, world");
        }
    }

more complicated example: insertion sort

    import java.util.Vector;
    import java.lang.Integer;
    import java.io.BufferedReader;
    import java.io.InputStreamReader;
    import java.io.IOException;

    class InsertionSort {       // has to have same name as file
        static void insSort(int[] V) {
            for (int i = 1; i < V.length; i++) {
                // note weird syntax of /for/ loop
                int curVal = V[i];
                int pos = i;
                while (pos > 0 && V[pos-1] > curVal) {
                    // parens required around condition
                    V[pos] = V[pos-1];
                    pos--;      // decrement operator
                }
                V[pos] = curVal;
            }
        }

        public static void main(String[] args) {
            BufferedReader in =
                new BufferedReader(new InputStreamReader(System.in));
            Vector<Integer> nums = new Vector<Integer>();
            while(true) {
                String line = "";
                    // initialization required for "definite assignment"
                try {
                    line = in.readLine();
                } catch (IOException e) {
                    // handler required, because readLine can raise
                }
                if (line.equals("")) break;
                int num = Integer.parseInt(line);
                nums.add(num);  // append
            }
            int[] A = new int[nums.size()];
            // There exists a toArray() method on Vectors that would
            // fill in A in one fell swoop, but only with capital-I
            // Integers, not with ints.
            for (int i = 0; i < nums.size(); i++) {
                A[i] = nums.get(i);
            }
            insSort(A);
            for (int i = 0; i < nums.size(); i++) {
                System.out.println(Integer.toString(A[i]));
            }
        }
    }