for distribute deployment use, 
usage `allssh -f hostname_file "cmd"`
or    `allscp -f hostname_file src_file dst`

a simple cmdline calculater, add to path first, set `chmod +x calc`, 
usage `calc "1+2**5"`

get random lines from a huge stdin input, 
usage `cat huge_file.txt|python randline.py 100`
or    `randline 100 huge_file.txt`

stdin_reader: cluster stdin inputs by key, for mapreduce uses

key files set operators, support set union/difference operators ets.