my eclipse.ini

Just discovered how to tweak and optimize eclipse startup and running performance:

startup
plugins/org.eclipse.equinox.launcher_1.2.0.v20110502.jar
--launcher.library
plugins/org.eclipse.equinox.launcher.gtk.linux.x86_64_1.1.100.v20110505
-product
org.eclipse.epp.package.jee.product
--launcher.defaultAction
openFile
-showsplash
org.eclipse.platform
--launcher.XXMaxPermSize
256m
--launcher.defaultAction
openFile
-vmargs
-Djava.library.path=/usr/lib/jni
-Dosgi.requiredJavaVersion=1.5
-XX:PermSize=256m
-XX:MaxPermSize=256m
-XX:+UseParallelGC
-Xms1024m
-Xmx1024m
-Xss4m

sources:
http://stackoverflow.com/a/7776565/376240

http://www.beyondlinux.com/2011/06/25/speed-up-your-eclipse-as-a-super-fast-ide/

java's shortcomings

Will keep adding to this list as and when I get more information.

Here are some things I take for granted in Python (and sometimes in C++ too) that aren't available in Java:

- it doesn't have support for multiline strings

- it doesn't support switching on strings (at least until jdk7)

- it doesn't allow default values for method arguments

linux: network manager keeps removing the nameserver i set in resolv.conf!

I want to always have Google's public DNS servers (8.8.8.8, 8.8.4.4) in my /etc/resolv.conf

However my WiFi settings are set to DHCP (for both office and home) and whenever I get a DHCP address, I also get the DNS servers configured on the DHCP server. These server settings overwrite my /etc/resolv.conf and I lose the

Having to set the nameservers manually in /etc/resolv.conf on each DHCP connection is too painful, so I found a simple and effective solution to this problem:

$ sudo vim /etc/dhcp3/dhclient.conf

# ensure the following line is uncommented in dhclient.conf:

# prepend domain-name-servers 8.8.8.8,8.8.4.4;

$ sudo service network-manager restart

This configures the DHCP client to always prepend the list of DNS servers obtained from DHCP with "8.8.8.8, 8.8.4.4" - and it works like a charm!

java: how to easily check if an element is present in an array

I'm spoiled by Python - it's so easy to do some things like check the presence of an item in a list:

mylist = ['a', 'b', 'c']
if 'a' in mylist:
     print "It's there!"

So what's the equivalent of this in Java?

if( Arrays.asList("a","b","c").contains("a") )
    system.out.println( "It's there!" );

Thanks to this stackoverflow discussion for the answer.

how to add multiple ip addresses to loopback and ping an AVD's host machine

From my Android Virtual Device I was trying to figure out how to connect to a service running on the same machine running the emulator.

For example, let's say I'm running Apache on my laptop, and also running the AVD on my laptop. In a browser on my laptop I can type "http://localhost/index.html" to test the index.html present in my Apache webroot.

But if I put "http://localhost/index.html" in the Android browser in the AVD, I don't get anything. That's because 'localhost' refers to the AVD itself, not the host outside the AVD.

This stackoverflow question saved the day: it turns out that from within the AVD you can ping the host machine at 10.0.2.2 - this is a kind of hard-coded virtual IP address in Android emulators for the host box.


Next, I wanted to make 10.0.2.2 go to localhost so that when I play a URL from the logs like http://10.0.2.2:8080/sms/srs?merch_txn_id=AK0AqgCkAMIAwwB5AOMAeA%3D%3D&i3p_db=ptsqa_fortumo3&i3p_host=10.0.2.2%3A5432&country=US
I don't want to have to replace 10.0.2.2 with localhost every time in every URL.

This part of the puzzle was solved by this very helpful link : I simply had to create a virtual IP address for the loopback device via:
ip -4 addr add 10.0.2.2/32 dev lo

After this we can see that 10.0.2.2 is an alias for the loopback interface, "lo":

[02:24:26] ~ $ ip addr
1: lo:  mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet 10.0.2.2/32 scope global lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever

does I3P leak memory?

I was suspecting my tomcat6 test app (I3P) was guilty of a memleak.

So I installed munin and munin-node on my box so that I could get pretty memory curves. The default munin setup doesn't plot graphs for specific processes out of the box. I eventually figured out that 'multips_memory' was the plugin for the job.

I was trying to get munin's multips_memory plugin to show me the RSS (Resident Set Size, not the other one :P - see 'man ps') of tomcat6. I wasn't getting any values in munin's multips_memory for "tomcat6" because multips_memory only checks the command name (which isn't 'tomcat' in my case). Tomcat's command line is a huge mess:

/usr/lib/jvm/java-6-sun/bin/java -Djava.util.logging.config.file=/var/lib/tomcat6/conf/logging.properties -Djava.awt.headless=true -Xmx128m -XX:+UseConcMarkSweepGC -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Xms512m -Xmx512m -Djava.endorsed.dirs=/usr/share/tomcat6/endorsed -classpath /usr/share/tomcat6/bin/bootstrap.jar -Dcatalina.base=/var/lib/tomcat6 -Dcatalina.home=/usr/share/tomcat6 -Djava.io.tmpdir=/tmp/tomcat6-tmp org.apache.catalina.startup.Bootstrap start 
 
The command name is thus /usr/lib/jvm/java-6-sun/bin/java which doesn't contain the string "tomcat" that I'm interested in. So that's why multips_memory couldn't find tomcat6 on my system... Great, here comes another tweakathon :P

So I went about adjusting the multips_memory code to suit my purposes:

[SNIP]
.
.
.
    ps -eo $monitor,args | gawk '
BEGIN              { total = "U"; } # U = Unknown. 
/grep/             { next; }
/'"$name"'/        { total = total + ($1*1024); }
END                { print "'"$fieldname"'.value", total; }'
done
.
.
.
[/SNIP]

What the above snippet does is match against the entire command+args of the processes against the string of interest using gawk. In other words, I'm now using "ps -eo args" instead of "ps -eo comm" which is necessary to find "tomcat6" in /usr/bin/java's arguments. Also, I changed the gawk regex match to search the entire line (not just $2 since the matching args for my search string could be $3 or $4 etc). I also made the search more inclusive by matching a substring instead of the exact string name  (removed the ^ and $ from the regular expression).

It works like a charm. Munin is now reporting beautiful (and worrying) memory graphs for my selected processes:

And then it struck me that this is pretty handy code. I sometimes need to see how much RAM a particular process is taking.

Every so often I see bad stuff about the tomcat app I'm testing:

4 Nov, 2011 12:58:23 AM com.aaa.bbb.application.modules.AppLauncherModule$1 uncaughtException SEVERE: Uncaught exception from Thread[Timer-0,5,main] java.lang.OutOfMemoryError: Java heap space

in the tomcat logs [/var/log/tomcat6/catalina.out]. The OOM forces a "sudo service tomcat6 restart" - really it must be a memleak.

So here's the result of this effort - a shell script inspired by the multips_memory munin plugin that that tells you how much memory all the instances of Java (e.g.) are consuming. See the usage() below for more details.

#!/bin/bash
#
# meminfo: A simple utility to display the memory usage of given process(es)
#
###############################################################################

# Default values of arguments:
VERBOSE=0
MEMORY_TYPE=rss
ARGS_TYPE=args
THIS_PROGRAM=$(basename $0)



usage()
{
cat << EOF

USAGE: $THIS_PROGRAM [arguments]

SUMMARY: A simple utility to display the memory consumption of given process(es) on this machine.

ARGUMENTS: (all optional)
    -h      Show this message
    -a      The type of arguments specified in 'ps -o'. Can be either 'args' or 'comm' (default: args)
                args: match against the full command name + argument 
                comm: match against the command name only
    -m      Specify memory type (default: rss) - see "man ps"
    -p      The process_string: can be simply a name or a regular expression.
                This argument is optional: if not supplied, all processes are considered.
    -v      Verbose mode: show debugging information

Each line of 'ps -e' is matched against the string using gawk: so you may have to escape special characters like '/' and ':" etc for gawk regex matching.

EXAMPLES:
$THIS_PROGRAM tomcat6
[show tomcat6 RSS memory usage]

$THIS_PROGRAM java
[show total memory usage by all java processes]

$THIS_PROGRAM -m vsz \\/usr\\/bin\\/java.*eclipse.*
[show memory VSZ taken by eclipse]

$THIS_PROGRAM ".usr.bin.java.+eclipse.+"
[simpler version of the above example]

$THIS_PROGRAM "\/usr\/bin\/java -Djava.library.path=\/usr\/lib\/jni -Dosgi.requiredJavaVersion=1.5 -XX:MaxPermSize=256m -Xms40m -Xmx512m -jar \/home\/ambar\/workspace\/tools\/eclipse\/\/plugins\/org.eclipse.equinox.launcher_1.2.0.v20110502.jar"
[very-specific command and args]

EOF
}


while getopts "hvm:a:p:" OPTION
do
    case $OPTION in
        h)
            usage
            exit 0
            ;;
        v)
            VERBOSE=1
            ;;
        a)
            ARGS_TYPE=$OPTARG
            ;;
        m)
            MEMORY_TYPE=$OPTARG
            ;;
        p)
            PROCESS_STRING=$OPTARG
            ;;
        ?)
            usage
            exit 1
            ;;
    esac
done



# another way to set default values, not needed here though
#: ${MEMORY_TYPE:=rss}
#: ${ARGS_TYPE:=args}
#: ${VERBOSE:=0}


if [[ -z $PROCESS_STRING ]]  # if no process name, then override ARGS_TYPE to args so that we calculate the FULL memory usage of all processes
then
    ARGS_TYPE=args
fi

ps -eo $MEMORY_TYPE,$ARGS_TYPE | gawk '
BEGIN                   { total = "U"; } # U = Unknown. 
/'$THIS_PROGRAM'/       { next; }
/grep/                  { next; }
/'"$PROCESS_STRING"'/   { total = total + ($1*1024); if('$VERBOSE'==1) {print "\n\t", $0; print "\tCUMULATIVE USAGE: ", total} }
END                     { mbs = total/(1024*1024); printf("\nTotal '$MEMORY_TYPE' memory used by all '$PROCESS_STRING' processes: %d bytes == %11.3f MB\n", total, mbs); }'

I learnt quite a bit: it's the first time I used getopts, basename, and integrated an awk script (that consumes bash variables) in a shell script. The whole endeavor seemed like a pointless digression at first, but now I think it was totally worth my time :)

And now it's time to show off the results of this little adventure:

[02:43:27] /var/log/tomcat6 $ meminfo -p eclipse -a args -m vsz

Total vsz memory used by all eclipse processes: 5109342208 bytes ==    4872.648 MB
[02:43:36] /var/log/tomcat6 $ meminfo -p tomcat6

Total rss memory used by all tomcat6 processes: 474861568 bytes ==     452.863 MB
[02:43:41] /var/log/tomcat6 $ meminfo 

Total rss memory used by all  processes: 4642054144 bytes ==    4427.008 MB

python: subtitle_delay_adjuster

Motivation: Couldn't find the perfect subtitles (.srt) file for a relatively-obscure movie? Are the subs in your .srt file off by a few seconds - just enough to irritate you, but not enough to ditch the awesome flick you're watching, AND are you feeling too lazy to tweak the subtitle offset in vlc manually?

This little proggie might just save the day  ^_^

#!/usr/bin/python2.7

import re
from datetime import datetime, timedelta
from functools import partial
import argparse



def replace_time(matchobj, time_diff):
    if matchobj.group(1) not in [None, '']:
       x = (datetime.strptime(matchobj.group(1), "%H:%M:%S") + time_diff).strftime("%H:%M:%S")
    

    if matchobj.group(3) not in [None, '']:
       y = (datetime.strptime(matchobj.group(3), "%H:%M:%S") + time_diff).strftime("%H:%M:%S")
    
    return x + matchobj.group(2) + y



def main():
    parser = argparse.ArgumentParser(
        description = 'subtitle_delay_adjuster: delay or advance all subtitles in an srt file by a given number of seconds',
        epilog = 'example: "%(prog)s -2 Thank.You.For.Smoking.2005.srt" would make all subs in the srt file appear 2 seconds earlier'
    )
    parser.add_argument('seconds', action='store', type=int, help='number of seconds by which to delay subtitles: use a negative number to advance subs instead of delaying them')
    parser.add_argument('srt_file', action='store', help='name of the srt_file to process')    
    args = parser.parse_args()

    time_diff = timedelta(seconds = args.seconds)


    infile = file(args.srt_file, 'r')
    outfile = file('out.srt', 'w')

    inlines = infile.readlines()

    for line in inlines:
        #print "line before sub: " + line
        newline = re.sub('(\d\d:\d\d:\d\d)(.*-->.*)(\d\d:\d\d:\d\d)', partial(replace_time, time_diff=time_diff), line)
        #print " line after sub: " + newline
        outfile.write(newline)

    infile.close()
    outfile.close()

    print "\n\n\nNew subs are ready! File: out.srt"




if __name__ == '__main__':
    main()

It certainly did save my day when I was trying to get the right subs for one of my favorite movies, "Thank You for Smoking" :-)

python: how to fix 'fatal error: Python.h: No such file or directory'

Was trying to install PyYAML. Got the latest tarball from the PyYAML website, and ran the usual:

sudo python setup.py install

which resulted in:

running install
running build
running buildpy
creating build
creating build/lib.linux-i686-2.6
creating build/lib.linux-i686-2.6/yaml
copying lib/yaml/constructor.py -> build/lib.linux-i686-2.6/yaml
.
.
.
running buildext
creating build/temp.linux-i686-2.6
checking if libyaml is compilable
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c build/temp.linux-i686-2.6/checklibyaml.c -o build/temp.linux-i686-2.6/checklibyaml.o
checking if libyaml is linkable
gcc -pthread build/temp.linux-i686-2.6/checklibyaml.o -lyaml -o build/temp.linux-i686-2.6/checklibyaml
building 'yaml' extension
creating build/temp.linux-i686-2.6/ext
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c ext/yaml.c -o build/temp.linux-i686-2.6/ext/yaml.o
ext/yaml.c:4: fatal error: Python.h: No such file or directory
compilation terminated.
error: command 'gcc' failed with exit status 1


Google quickly yielded the solution. The missing Python.h was in the python-dev package. Since I was running python2.6.6, I simply needed to do:

sudo apt-get install python2.6-dev

after which compilation and installation was successful:

running install
running build
running buildpy
running buildext
building '_yaml' extension
.
.
.
running installegginfo
Writing /usr/local/lib/python2.6/dist-packages/PyYAML-3.10.egg-info


git: how to ignore certain file types globally

I wanted to tell git not to ever include .pyc files in any project, anywhere on my system, instead of having to specify a separate .gitignore file in every python project directory. A simple google search solved the problem; here's one way to do this:

Create a ~/.gitignore file in your home directory:

.DS_Store
*.pyc

Then run:
git config --global core.excludesfile ~/.gitignore

That's it!

 

thanks to [source]

linux: vnstat rocks!

vnstat is a superb tool to monitor monthly bandwidth usage.

I get notified by my ISP when I hit my monthly download quota (25 GB) that my speed will now be reduced to 256 kbps. Sometimes I'm left wondering how the heck I hit 25 gigs of downloading. So I started looking for a tool on Ubuntu that would monitor my bandwidth usage and show me daily/weekly/monthly download totals.

Requirements: It should work silently and unobtrusively in the background, and it should start automatically on reboot like a daemon. It would be nice to have it display graphical graphs. Also nice to have it display realtime stats (e.g. current rx and tx speeds).

There are quite a few tools that I found: bandwidthd, bwmon, bwbar etc (complete list here: http://www.ubuntugeek.com/bandwidth-monitoring-tools-for-ubuntu-users.html).

I didn't try all of them, but the most popular (or the one that appears at the top of the google search results for "bandwidth monitor tool ubuntu") is bandwidthd, and I just didn't have the patience to get it to work. There's no user manual, no real how-to and I gave up quickly on it.

vnstat saved the day. It exactly meets my requirements. You don't need to install it from the tarball either (in fact, that didn't work too well for me, I kept getting post-install configuration errors), and if you're on ubuntu, vnstat is in the standard apt repositories.

vnStat is a console-based network traffic monitor for Linux and BSD that keeps a log of network traffic for the selected interface(s). It uses the network interface statistics provided by the kernel as information source. This means that vnStat won't actually be sniffing any traffic and also ensures light use of system resources.

 

[08:17:59] ~ $ vnstat -d

eth1  /  daily
     day         rx      |     tx      |    total    |   avg. rate
 ------------------------+-------------+-------------+---------------
  08/24/11    134.81 MiB |    7.24 MiB |  142.05 MiB |   13.47 kbit/s
  08/25/11     84.21 MiB |    5.63 MiB |   89.85 MiB |   24.82 kbit/s
 ------------------------+-------------+-------------+---------------
 estimated       244 MiB |      14 MiB |     258 MiB |
[08:18:04] ~ $ vnstat -s
                  rx      /      tx      /     total    /   estimated
eth1:
 Aug '11    219.02 MiB  /   12.88 MiB  /  231.90 MiB  /  293.00 MiB
 yesterday    134.81 MiB  /    7.24 MiB  /  142.05 MiB
 today     84.21 MiB  /    5.63 MiB  /   89.85 MiB  /     258 MiB

 

python interview questions - part 1

1. Q:What is PYTHONPATH?
   A: Python uses the directories listed in PYTHONPATH to find a module.
2. Q: How can I see the PYTHONPATH on my system?
   A: Several ways:          

    

   • From the shell prompt: echo $PYTHONPATH
   • Programmatically in python itself:
     

     >>> import sys
     >>> sys.path
     ['', '', '', '/usr/lib/python2.6/dist-packages/pygame/tests', '/usr/lib/python2.6/dist-packages/pygame', '', '/usr/lib/python2.6', '/usr/lib/python2.6/plat-linux2', '/usr/lib/python2.6/lib-tk', '/usr/lib/python2.6/lib-old', '/usr/lib/python2.6/lib-dynload', '/usr/local/lib/python2.6/dist-packages', '/usr/lib/python2.6/dist-packages', '/usr/lib/python2.6/dist-packages/PIL', '/usr/lib/python2.6/dist-packages/gst-0.10', '/usr/lib/pymodules/python2.6', '/usr/lib/python2.6/dist-packages/gtk-2.0', '/usr/lib/pymodules/python2.6/gtk-2.0']
     

3. Q: How can I add a directory to the PYTHONPATH?
   A: Programmatically, in python itself:          

    

   #!/usr/bin/python
   
   import sys
   sys.path.append('path/to/my/modules/')
   
   # now import a module/.py file that resides in "path/to/my/modules"
   import my_module
   

4. Q: What are some standard python modules?
   A: Take a look at the Python Standard Library Reference Manual: http://docs.python.org/library/index.html
   Some standard modules are: os, sys, string, re, socket, datetime, math, commands [a useful wrapper around ps.popen() for running unix commands], httplib, urllib, json, ssl, thread, getopt, optparse, random
5. Q: What are packages in python?
   A: Packages are used to organize and group modules. Packages are just folders of modules with a special init.py file that indicates to Python that this folder is special because it contains Python modules. Packages are just a convenience to hierarchically organize modules.
6. Q: What is init.py used for?
   A: Source: http://effbot.org/pyfaq/what-is-init-py-used-for.htm
   It is used in marking a directory as a package directory. If you have the files:
   
mydir/mypackage/init.py
mydir/mypackage/mymodule.py

   and mydir is on the PYTHONPATH, you can import the code in mymodule.py via from mypackage import mymodule
   or via import mypackage.mymodule          

    

   If you remove the init.py file from the mypackage directory, Python will NOT look for modules inside the mypackage directory, and you will not be able to import the mymodule module.

   The init.py file is usually empty. Furthermore, init.py is the first file to be loaded in a package, so you can use it to execute initialization code that you want to run each time a module is loaded, or specify the submodules to be exported.

7. Q: What is the init function for?
   A: init is similar to a constructor for a class in Python. It is a way to specify default values for an object's data members when you create an object. These values are set in the class definition.          

    

   The init() method is called immediately after an instance of the class is created. It would be tempting — but technically incorrect — to call this the “constructor” of the class. It’s tempting, because it looks like a C++ constructor (by convention, the init() method is the first method defined for the class), acts like one (it’s the first piece of code executed in a newly created instance of the class), and even sounds like one. Incorrect, because the object has already been constructed by the time the init() method is called, and you already have a valid reference to the new instance of the class.

   The first argument of every class method, including the init() method, is always a reference to the current instance of the class, called "self".

   Example:

   class Point:
       def __init__ (self, arg1=0, arg2=0):
           self.x = arg1
           self.y = arg2
   
       def display(self):
           print "Point::display(): x=" + str(self.x) + " and y=" + str(self.y)
   
   p1 = Point(5, 8);
   p2 = Point();
   p1.display();
   p2.display();
   

   results in:
   
Point::display(): x=5 and y=8
Point::display(): x=0 and y=0


8. Q: What is main used for?
   A: source: http://effbot.org/pyfaq/tutor-what-is-if-name-main-for.htm
   The if name == "main": ... trick exists in Python so that our Python files can act as either reusable modules, or as standalone programs.         

    

   Example:
   square.py :

   def square(x):
       return x*x
   
   if __name__ == '__main__' ;
       print "square.py | the square of 10 is: " , square(10)
   

   test.py:

   import square
   
   print "test.py | the square of 20 is: " , square(20)
   

   execution:

   $ python square.py
   square.py | the square of 10 is: 100
   $ python test.py
   test.py | the square of 20 is: 400
   

9. Q: What is a lambda function? Explain with an example. Typical usage?
   A: A lambda function is a shorthand for an anonymous function.
   The form is lambda <arguments>: <resultant-expression>
    
10. Q: What is the map function? Explain with an example. Typical usage?
    A: map applies a function to every element of a list and returns the resultant list.
    PNEMONIC: Hence it "maps" a function to every element of a list.
    Example:         

     

    >>> map ( lambda x: x*2, [1,2,3] )
    [2, 4, 6]
    

11. Q: What is the reduce function? 
    A: reduce takes as input a function and a list. The function must take exactly two arguments. reduce applies the function to the first two successive elements of the list from left to right, and then replaces the first two elements with the result of the function.
    PNEMONIC: Hence it "reduces" the number of elements in the list by one on each operation, until eventually only one element is left.Example:         

     

    >>> # this effectively sums the elements in the list by doing ((((1+2)+3)+4)+5)
    >>> reduce( lambda x,y : x+y, [1,2,3,4,5] )
    15
    

12. Q: What is the filter function?
    A: filter applies a function to every element of a list. Unlike, map, however, the function must return either True or False for each check. filter returns a list of all elements that pass this check.
    PNEMONIC: Hence it "filters" those elements that pass the test of the function.         

     

    Example:

    >>> # get those elements in the list that are divisible by 3
    >>> filter ( lambda x : x%3==0 , [1,2,3,4,5,6])
    [3,6]
    

13. Q: What is a list comprehension? Explain with an example. Typical usage?
14. Q: What is pass used for?
    A: The pass statement in Python is like a empty set of curly braces ({}) in Java or C. 
15. Q: How do you create an empty tuple?
    A: t = ()
16. Q: How do you create a tuple containing one element?
    A: t = (something, ) #note the comma at the end - this is the only way to specify a single-element tuple 
17. Q: How can you use the and-or trick safely (to simulate a C-style ternary expression)?
    A: <exprtotest> and [a] or [b])[0] 
18. Q: How can you use a much-nicer and more-readable ternary style expression in Python?
    A: Example: map(lambda x:x*2, range(0,20)) if (2 > 1) else ""
19. Q: How can you delete an element or a slice of elements from a list?
    A: Using the del statement
    
    >>> a = [-1, 1, 66.25, 333, 333, 1234.5]
    >>> del a[0]
    >>> a
    [1, 66.25, 333, 333, 1234.5]
    >>> del a[2:4]
    >>> a
    [1, 66.25, 1234.5]
    >>> del a[:]
    >>> a
    [] 

     

     

20. Q: What are ".pyc" files and when are they generated?
    A: Importing a module is a relatively costly affair, so Python does some tricks to make it faster. This .pyc file is useful when you import the module the next time from a different program - it will be much faster since a portion of the processing required in importing a module is already done. Also, these byte-compiled files are platform-independent.
    source
21. Q: What is the use of the inbuilt dir function?
    A: You can use the built-in dir function to list the identifiers that an object defines. When you supply a module name to the dir() function, it returns the list of the names defined in that module. When no argument is applied to it, it returns the list of names defined in the current module.
    source
22. Q: Explaing duck-typing wrt Python.
    A: Duck-typing can be simply explained as, "As long as you get the job done, we don't care who your parents are." 

     

    In other words, as long as an object can perform these actions:

    • quackLikeADuck()
    • walkLikeADuck()
    • swimLikeADuck()

    then that object is a Duck for Python. It doesn't matter which class the object is derived from (who its parents are). This greatly improves polymorphism and thus flexibility. Duck-typing avoids tests using type() or isinstance()

    Example: The canonical examples of duck typing in Python are file-like classes. You can use cStringIO to handle a string like a file, or GzipFile to handle a gzipped-object like a file. Similarly you can treats sockets like files too. However, sockets lack the 'tell()' method and so cannot be used everywhere that a file can be used. This shows the flexibility of duck typing: a file-like object needs to implement methods only that it is able to. Thus it can only be used in situations where it makes sense. Where the object is expected to support the 'tell()' method, and it doesn't, it can throw a "TellException" instead, which makes it easy to handle the unsupported-method-exception in the calling code and then move on. This is called as EAFP: "Easier to Ask Forgiveness than to ask for Permission" style programming.

network monitoring tools on linux

netactview: a network activity viewer for linux

I was trying to find a linux equivalent for "diamondcs port explorer"/tcpview/cports. It was surprisingly hard to get this information: took well over an hour, but I finally got exactly what I needed: netactview

netactview dynamically updates what ports are in use by what application, just like tcpview/cports/etc

It's available here:
http://netactview.sourceforge.net/download.html



iftop: display bandwidth usage on an interface

iftop needs libpcap and libcurses, and helps identify which connection is sucking out all your bandwidth. Quoting the home page, "Handy for answering the question "why is our ADSL link so slow?"

iftop can also show source and destination ports in each network connection (press ? for the help screen, just like you would in top).

iftop home page

Ubuntu!!!

A person with ubuntu is open and available to others, affirming of others, does not feel threatened that others are able and good, for he or she has a proper self-assurance that comes from knowing that he or she belongs in a greater whole and is diminished when others are humiliated or diminished, when others are tortured or oppressed.

-- Archbishop Desmond Tutu, 1999

phone screen questions

Phone screen technical questions

What is the difference between client-side and server-side scripting? Under what situation will you use which type?

Give me some examples of each type of scripting technology.

Describe the company to him, what kind of work is done here – brief intro to the project/product.

Instructions

1. Go through those questions with the candidate on the phone, and fill in the gathered answers in the space provided after each question
2. Pick one experience on their resume and ask the candidate a question or two to verify their participation and role in that experience.

General

1. What is the difference between a process and a thread?
   A process has its own address space; a thread is part of a process and uses the address space of its parent process.
   
   
2. What is the difference between a heap and a stack?
   A heap is memory used to store non-local data. A stack can be used to only store local data (ie, data that can be accessed only by the function that is executing, or any function that it calls).
   
   
3. What is an access violation?
   Illegal access to a memory location, or accessing a memory location that is not mapped.
   
   
4. How do you determine the code location of an access violation that occurs in the field?
   Configure the process to generate an image dump file and then load this in the debugger to view the call stack.

MultiThreaded Experience

1. What is the difference between a semaphore and a lock?
   A lock allows exactly one entity (thread, process) to access a protected resource; a semaphore allows a specific number (controlled number) of entities (processes, threads) to allow a resource.
   
   
2. What is a deadlock?
   A situation where there are two resources protected by two locks, A and B. One process (or thread) comes along, locks A, and wants to lock B. But another process (or thread) has locked B and is waiting to lock A. Neither one can proceed and this situation is called a deadlock.

C/C++

1. What are the two arguments to the function “main”?
   argc, and argv
   Count of arguments and an array (or vector) of string arguments.
   
   
2. What is a C++ class?
   It is a type of data structure that allows for the code and data associated with a logical object to be abstracted or packaged together.
   
   
3. What is a virtual function?
   A function of a class that can be overridden by derived classes.
   
   
4. What is the difference between a private member and a protected member of a C++ class?
   Private allows access by methods of the class (or by friends of the class).  Protected allows access by derived classes as well.
   
   
5. What is a Reference in C++?
   Like a pointer, it is the address of an object, but syntactically, it behaves like the object itself.
   
   
6. Why are templates important to C++?
   No root base class exists for creation of generic containers as in Java or other rooted OO languages, and templates allow enforcement of type safety.

COM/COM+

1. What are the three methods on the IUnknown interface?
   AddRef, Release, QueryInterface.
   
   
2. How do you create a new com object?
   CoCreateInstance
   
   
3. What are the different apartment threading models in COM?
   STA (single threaded), MTA (multi threaded), TNA (thread neutral) and Both/Any (allows STA, MTA or TNA to match creator apartment)
   
   
4. What language is used to define COM interfaces?
   IDL.

Java

1. What is a Java Class?
   It is a type of data structure that allows for the code and data associated with a logical object to be abstracted or packaged together.
   
   
2. What package do you need to import for simple TCP/IP communications?
   java.net.*
   
   
3. What is the Java VM?
   Java programs are compiled to bytecode that is then executed by the Java Virtual Machine.
   
   
4. How do you create a pointer in Java?
   You don’t!
   
   
5. What is the java facility that allows you to inspect classes at runtime called?
   reflection

Networking:

1. What is a DMZ?
   De-Militarized Zone, or the network zone between two firewalls.
   
   
2. What is NAT?
   Network Address Translation - or a device that maps one IP address to another.
   
   
3. Why do you need technology like NAT?
   To map internal IP addresses/Ports (which are typically in the non-routable range) to external IP addresses/Ports.
   
   
4. What is the purpose of calling bind when listening on a TCP socket?

To specify a local end point (IP address and port) to accept connections on

IIS/ASP:

1. How are ASP pages different from HTML?
   ASP pages contain server side scripting.
   
   
2. What is a CSS file used for?
   CSS = cascading style sheet, used to specify formatting separately from the HTML content.

3. How do you perform client side validation on a form element?
   Typically, associate a client side validation script with an event on the HTML element.   .NET supports some declarative client side validation.

SQL Server

1. What is a join?
   A SQL operation that produces a single (logical) table from two or more tables, by matching one column in one table with a column in the other table.
   
   
2. How are inner and outer joins different?
   An inner join is where the result contains rows that have a match in the column values in both tables.   An outer join allows data from one of the tables to be included even if the join column data is null.
   
   
3. What is normalization?
   The design process that eliminates repetitive data.
   
   
4. Assume you have a SQL table with 30 million rows and you want to fetch a few records.  How do you ensure the query returns quickly?
   Ensure that the where and order by criteria are supported with appropriate indexes.

XML / XSLT

1. What is a DOM
   Document Object Model is a parsed, in memory XML document.

2. What is XSLT
   Extensible Style Language Transformations.
   
   
3. What is XSLT useful for?
   For converting XML data to any other format.
   
   
4. What techniques are normally used to embed an arbitrary XML document inside another as a text entity?
   Normally either XML entity encoding (e.g. “&” -> “&&”) or enclosing the data in a CDATA section.
   
   
   

Bill Gates on What Makes a Good Software Manager

source: http://www.worklifecoach.com/bill_gates.pdf


From the New York Times: What Makes a Good Manager (10/8/97) By BILL GATES.

RECENTLY I wrote about 10 qualities of a good employee, which prompted quite a few people to ask about the attributes of a good manager.

There isn't a magic formula for good management, of course, but if you're a manager, perhaps these tips will help you be more effective:

1 Choose a field thoughtfully. Make it one you enjoy. It's hard to be productive without enthusiasm. This is true whether you're a manager or employee.

2 Hire carefully and be willing to fire. You need a strong team, because a mediocre team gives mediocre results, no matter how well managed it is. One mistake is holding on to somebody who doesn't measure up. It's easy to keep this person on the job because he's not terrible at what he does. But a good manager will replace him or move him to where he can succeed unambiguously.

3 Create a productive environment. This is a particular challenge because it requires different approaches depending on the context. Sometimes you maximise productivity by giving everybody his or her own office. Sometimes you achieve it by moving everybody into open space. Sometimes you use financial incentives to stimulate productivity. A combination of approaches is usually required. One element that almost always increases productivity is providing an information system that empowers employees. When I was building Microsoft, I set out to create an environment where software developers could thrive. I wanted a company where engineers liked to work. I wanted to create a culture that encouraged them to work together, share ideas and remain motivated. If I hadn't been a software engineer myself, there's no way I could have achieved my goal.

4 Define success. Make it clear to your employees what constitutes success and how they should measure their achievements. Goals must be realistic. Project schedules, for example, must be set by the people who do the work. People will accept a "bottoms-up" deadline they helped set, but they'll be cynical about a schedule imposed from the top that doesn't map to reality. Unachievable goals undermine an organisation. At my company, in addition to regular team meetings and one-on-one sessions between managers and employees, we use mass gatherings periodically and E-mail routinely to communicate what we expect from employees. If a reviewer or customer chooses another company's product , we analyse the situation. We say to our people, "The next time around we've got to win. What's needed?" The answers to these questions help us define success.

5 To be a good manager, you have to like people and be good at communicating. This is hard to fake. If you don't enjoy interacting with people, it'll be hard to manage them well. You must have a wide range of personal contacts within your organisation. You need relationships - not necessarily personal friendships - with a fair number of people, including your own employees. You must encourage these people to tell you what's going on and give you feedback about what people are thinking about the company and your role in it;

6 Develop your people to do their jobs better than you can. Transfer your skills to them. This is an exciting goal, but it can be threatening to a manager who worries that he's training his replacement. If you're concerned, ask your boss: "If I develop somebody who can do my job super well, does the company have some other challenge for me or not?" Many smart managers like to see their employees increase their responsibilities because it frees the managers to tackle new or undone tasks. There's no shortage of jobs for good managers. The world has an infinite amount of work to be done.

7 Build morale. Make it clear there's plenty of goodwill to go around and that it's not just you or some hotshot manager who's going to look good if things go well. Give people a sense of the importance of what they're working on - its importance to the company, its importance to customers.

8 Take on projects yourself. You need to do more than communicate. The last thing people want is a boss who just doles out stuff. From time to time, prove you can be hands-on by taking on one of the less attractive tasks and using it as an example of how your employees should meet challenges.

9 Don't make the same decision twice. Spend the time and thought to make a solid decision the first time so that you don't revisit the issue unnecessarily. If you're too willing to reopen issues, it interferes not only with your execution but also with your motivation to make a decision in the first place. People hate indecisive leadership; However, that doesn't mean you have to decide everything the moment it comes to your attention. Nor that you can't ever reconsider a decision.

10 Let people know whom to please. Maybe it's you, maybe it's your boss, and maybe it's somebody who works for you. You're in trouble and risking paralysis in your organisation when employees start saying to themselves: "Am I supposed to be making this person happy or this other person happy? They seem to have different priorities.

"I don't pretend that these are the only 10 approaches a manager should keep in mind. There are lots of others. Just a month ago I encouraged leaders to demand bad news before good news from their employees. But these 10 ideas may help you manage well, and I hope they do."

-- Bill Gates

linuxbasics: use dd to create a file of any size

 

dd  if=/dev/zero  of=mytestfile  bs=1048576  count=1