#!/usr/bin/env python

def func1(x=[]):
    x.append(1)
    return 'x = %15s, id(x) = %s' % (x, id(x))

def func2(x=None):
    if x is None:
        x = []
    x.append(1)
    return 'x = %15s, id(x) = %s' % (x, id(x))

for f in (func1, func2):
    print '%s %s' % (f.__name__, f())
    print f.__name__, f()
    print f.__name__, f()
    print f.__name__, f([2])
    print f.__name__, f()
    print

$ ./gotcha.py 
func1 x =             [1], id(x) = 3084437356
func1 x =          [1, 1], id(x) = 3084437356
func1 x =       [1, 1, 1], id(x) = 3084437356
func1 x =          [2, 1], id(x) = 3084466828
func1 x =    [1, 1, 1, 1], id(x) = 3084437356

func2 x =             [1], id(x) = 3084466828
func2 x =             [1], id(x) = 3084466828
func2 x =             [1], id(x) = 3084466828
func2 x =          [2, 1], id(x) = 3084466828
func2 x =             [1], id(x) = 3084466828

The scenario is this: a value would be supplied by the user, and I had to pull out some hard-wired information based on this value. So, suppose you were writting a script that referenced file types arranged by extenstions and was selected by the user at run time. This would be easily solvable in the following:

#!/usr/bin/env bash

# List of variables maybe in some other file
JPG_FILE_PATH="/opt/path/one"
DOC_FILE_PATH="/opt/path/two"
MP3_FILE_PATH="/opt/path/three"
XLS_FILE_PATH="/opt/path/four"

get_file_path() {
    local ID=${1-''}
    # Sets FILE_PATH to the desired value. If not exist then null.
    FILE_PATH=$(eval "echo \${$(echo ${ID}_FILE_PATH)"-''})
}

get_file_path "MP3" 
echo $FILE_PATH

$ ./test_pre.sh
/opt/path/three

The above snippet -- admittedly a bit humorous -- is very useful in several situations. I happened to use it in creating a shell library of functions and paths that are used by others in the easy creation of scripts around Oracle RDBMS.

<div class="widget-linkroll widget">
    <h3 class="widget-header">Interesting Links</h3>
    <div class="widget-content">
    <MTLinks>
    <MTLinksHeader>
    <ul>
        </MTLinksHeader>
            <li><a href="<$MTLinkURL$>"><$MTLinkName$>: <$MTLinkDescription$></a></li>
        <MTLinksFooter>
    </ul>
    </MTLinksFooter>
    </MTLinks>
    </div>
    
</div>

<div class="widget-linkroll widget">
<h3 class="widget-header">Interesting Links</h3>
  <div class="widget-content">
    <mt:Tags type="asset" sort_by="name">
      <ul class="widget-list">
      <li><h4><mt:TagName></h4></li>
      </ul>
      <MTSetVarBlock name="linktag"><mt:TagName /></MTSetVarBlock>
      <ul class="widget-list">
        <mt:Assets type="link" tag="$linktag">
          <li><a href="<mt:AssetURL>"><mt:AssetLabel escape="html">: <mt:AssetDescription></a></li>
        </mt:Assets>
      </ul>
    </mt:Tags>
  </div>
</div>

After choosing one of the two options -- or rolling your own -- click save and return back to the widgets page. Before publishing your blog so you can see your links, the final step is to place the widget in your selected widget set. Under "Widget Sets", select your layout and drag your newly created widget from "Available Widget" to "Installed Widgets". Once you have pressed "Save Changes" and the system finishes the update, you can now publish your blog.


Happy linking!

grub> root (hd0,0)
root (hd0,0)

or

grub> find /boot/grub/stage1
find /boot/grub/stage1
 (hd0,0)
grub> setup (hd0)

However, we received:

grub> find /boot/grub/stage1
Error 15: File not found

Well, that's not good! I considered trying

# dd if=/boot/grub/stage1 of=/dev/sda count=1

but didn't have the courage to do it and looking back on it now it wouldn't have worked anyway. So instead I ignorantly copied the MBR from the other disk as it was supposed to be a clone and applied it to the new disk using dd of course.

The outcome WAS NOT PRETTY! Grub could not find any partition. In short, the file allocation tables were all wrong. Not to worry, we just loaded up Winternals ERD and ran a lengthy scan on the disk. I figured the $2345245 software would surely bail us out of this mess. Wrong!

The solution was this gem of an open source beauty. I loaded this on a USB stick, booted off the Heron livecd, and ran the binary it ships with. Within minutes it found the correct partitions and we were able to restore the MBR with the correct file allocation tables.

However, we were just back to square one and needed to install Grub to the MBR. We figured out that what done us over in the first place was the fact the Ubuntu partition was not the active partition. Easily fixable:

# fdisk /dev/sda 
... 
Command (m for help): a 
Partition number(1-5): 2 
... 

At this point we were able to boot back into the livecd and run grub correctly. Lesson learned -- just because you've done something numerous times that should be straightforward -- backup!