Ideaz From Ur Brainz

/ tmp ( ) $ cat out_err_redirect_test . sh echo message to stdout echo message to stderr > & 2 / tmp ( ) $ bash out_err_redirect_test . sh message to stdout message to stderr # Message to stdout is redirected to dev null / tmp ( ) $ bash out_err_redirect_test . sh > / dev / null message to stderr # Message to stderr is redirected to dev null / tmp ( ) $ bash out_err_redirect_test . sh 2 > / dev / null message to stdout # Message to stderr and stdout is redirected to dev null / tmp ( ) $ bash out_err_redirect_test . sh > / dev / null 2 > / dev / null # Messaged to stdout is redirected to dev null , and stderr to configured stdout ( implies dev null ) / tmp ( ) $ bash out_err_redirect_test . sh > / dev / null 2 > & 1 # Message to stderr is redirected to stdout ( screen ) and stdout to dev null / tmp ( ) $ bash out_err_redirect_test . sh 2 > & 1 > / dev / null message to stderr

Below the tuple (1, 2, 3) is getting expanded as 3 arguments and the format representation is expecting to have 3 %s or %r to be printed, > > > print " %r " % ( 1 , 2 , 3 ) Traceback ( most recent call last ) : File " <stdin> " , line 1 , in < module > TypeError: not all arguments converted during string formatting > > > print " %s " % ( 1 , 2 , 3 ) Traceback ( most recent call last ) : File " <stdin> " , line 1 , in < module > TypeError: not all arguments converted during string formatting > > > print " %s " % str ( ( 1 , 2 , 3 ) ) ( 1 , 2 , 3 )

Perl looping of an array with index as well as the item stored in variables, /tmp$ cat loop_with_index.pl  my @arr=(1,2,3,4); while (my ($i, $x) = each(@arr)) {     print "$i: $x\n"; } /tmp$ perl loop_with_index.pl  0: 1 1: 2 2: 3 3: 4

To get the keys of a constant hashref you first need to learn that a constant is actually a function and hence use () to get the keys from it INPUT: $ cat perlConstant.pl use Data::Dumper; use constant FOOHASH => { "foo" => "bar", }; print FOOHASH->{"foo"}."\n"; foreach $key (keys %{FOOHASH()}) { FOOHASH->{$key} = "bar1"; } print FOOHASH->{"foo"}."\n"; foreach $key (keys %{FOOHASH}) { FOOHASH->{$key} = "bar2"; } print FOOHASH->{"foo"}."\n"; OUTPUT: $ perl perlConstant.pl bar bar1 bar1

There would be cases where large dictionaries are being embedded in the code (multiple pages in length) and users might append something to end of the dictionary, just assuming that its not already in the dictionary.  This could be easily avoided by following dict() instead of {} notation for dictionaries. > > > a = { . . . 'a' : 1 , . . . 'b' : 2 , . . . 'c' : 3 , . . . 'd' : 'nextpage' , . . . 'a' : 0 . . . } > > > print a { 'a' : 0 , 'c' : 3 , 'b' : 2 , 'd' : 'nextpage' } > > > a = dict ( . . . a = 1 , . . . b = 2 , . . . c = 3 , . . . d = 'nextpage' , . . . a = 0 . . . ) File " <stdin> " , line 6 SyntaxError : keyword argument repeated

When the regex being compiled in python which has multiple wild cards like plus or asterisks sequentially repeated, you will need to escape or else run into "multiple repeat error". This can happen with any of re module methods like search and sub etc, where the regex is compiled. > > > import re > > > re . compile ( " r++ " ) Traceback ( most recent call last ) : File " <stdin> " , line 1 , in < module > File " /usr/lib/python2.7/re.py " , line 190 , in compile return _compile ( pattern , flags ) File " /usr/lib/python2.7/re.py " , line 242 , in _compile raise error , v # invalid expression sre_constants . error : multiple repeat > > > re . compile ( " r** " ) Traceback ( most recent call last ) : File " <stdin> " , line 1 , in < module > File " /usr/lib/python2.7/re.py " , line 190 , in compile return _

Avoid using "/" at the end of the directory paths as they would generate empty filename when used with functions like os.path.split() > > > import os > > > os . path . split ( '/tmp/foo' ) ( '/tmp' , 'foo' ) > > > os . path . split ( '/tmp/foo/' ) ( '/tmp/foo' , '' ) Reference: https://docs.python.org/2/library/os.path.html

Class/Global variables are like CoW, only when the instances assign them values they have their own memory location allocated. For example in this case a.bar is assigned a value and hence it has different memory location allocated, but the same is not the case with b.bar >> > class Foo ( object ) : bar = None >> > repr ( Foo . bar ) 'None' >> > a = Foo ( ) >> > a . bar = 1 >> > repr ( Foo . bar ) 'None' >> > a . bar 1 >> > b = Foo ( ) >> > b . bar >> > repr ( b . bar ) 'None' >> > a . bar 1 >> > id ( Foo . bar ) 135796184 >> > id ( a . bar ) 151257264 >> > id ( b . bar ) 135796184

To enable nfs caching on ubuntu, sudo apt-get install cachefilesd sudo sed -i 's/nfs rw/nfs fsc,rw/' /etc/fstab service restart cachefilesd To use tmpfs instead of disk cache use this after making sure the runner has atleast 12G of memory, mount | grep fscache || mount -t tmpfs -o size=8192m tmpfs /fscache ls /fscache/disk0 || dd if=/dev/zero of=/fscache/disk0 bs=1M count=8191 sleep 15 ls /fscache/disk0 && echo 'y' | mkfs.ext4 /fscache/disk0 mount /fscache/disk0 /var/cache/fscache -t ext4 service cachefilesd restart

Proxy cannot be created for basic datatypes like list, dict, str and int. Proxy can be create for class instances only. Also proxy cannot be created for proxy of another instance. >>> import weakref >>> a = 'str' >>> b = weakref.proxy(a) Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: cannot create weak reference to 'str' object >>> a = 1 >>> b = weakref.proxy(a) Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: cannot create weak reference to 'int' object >>> a = [] >>> b = weakref.proxy(a) Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: cannot create weak reference to 'list' object >>> a = {} >>> b = weakref.proxy(a) Traceback (most recent call last):   File "<stdin>",

>>> def foo(x): ...    raise Exception('%s is invalid input' % x) ... >>> try: ...     foo(1) ... except Exception, e: ...     raise e                          # RE-RAISING EXCEPTIONS ... Traceback (most recent call last):   File "<stdin>", line 4, in <module>    # LOSES foo Exception: 1 is invalid input >>> try: ...     foo(1) ... except Exception: ...     raise                             # RAISING EXCEPTIONS ... Traceback (most recent call last):   File "<stdin>", line 2, in <module>   File "<stdin>", line 2, in foo          # STORES foo too Exception: 1 is invalid input >>>