I have downloaded this script named, pyAES.py and put it in a folder name codes, inside a Desktop directory of my Linux,According to this example,http://brandon.sternefamily.net/2007/06/aes-tutorial-python-implementation/When I type, ./pyAES.py -e testfile.txt -o testfile_encrypted.txtthe file pyAES.py should be executed.but I am getting this error,pi@raspberrypi ~/Desktop/Codes $ pyAES.py-bash: pyAES.py: command not foundthe output of ls -l command is,pi@raspberrypi ~/Desktop/Codes $ ls -ltotal 16-rw-r--r-- 1 pi pi 14536 Oct  8 10:44 pyAES.pyHere is the output after chmod +xpi@raspberrypi ~/Desktop/Codes $ chmod +x pyAES.py                              pi@raspberrypi ~/Desktop/Codes $pi@raspberrypi ~/Desktop/Codes $ pyAES.py-bash: pyAES.py: command not foundpi@raspberrypi ~/Desktop/Codes $and the command, chmod +x pyAES.py && ./pyAES.py gives the following error,-bash: ./pyAES.py: /usr/bin/python2: bad interpreter: No such file or directoryI have also tried moving the file in /usr/bin directory and then executing it,pi@raspberrypi /usr/bin $ pyAES.py-bash: /usr/bin/pyAES.py: /usr/bin/python2: bad interpreter: No such file or directorypi@raspberrypi /usr/bin $I can see the file is present in /usr/bin directory but it is still giving an error that  No such file or directory.I want to know why the Linux terminal is not executing the python script ?
Running python script from Linux Terminal
python;path;executable;shebang
It seems you have a badly-written shebang line. From the error you're getting:-bash: /usr/bin/pyAES.py: /usr/bin/python2: bad interpreter: No such file or directoryI'd say you should set the first line of /usr/bin/pyAES.py to#!/correct/path/to/pythonwhere the /correct/path/to/python can be found from the output of:type -P pythonIt's /usr/bin/python (not /usr/bin/python2) on my system.