rapid introduction to procedural programming ('hello''world!'then it means that python is on the system and is being invoked instead of python one solution to this is to change the py file association from python to python the other (less convenientbut safersolution is to put the python interpreter in the path (assuming it is installed in the default location)and execute it explicitly each time (this also gets around the windows file association bug mentioned earlier for examplec:\py eg\>path= :\python ;%pathc:\py eg\>python hello py it might be more convenient to create py bat file with the single line path= :\python ;%pathand to save this file in the :\windows directory thenwhenever you start console for running python programsbegin by executing py bat or alternatively you can have py bat executed automatically to do thischange the console' properties (find the console in the start menuthen right-click it to pop up its properties dialog)and in the shortcut tab' target stringappend the text / / :\windows\py bat(note the space beforebetweenand after the "/uand "/koptionsand be sure to add this at the end after "cmd exe"on unixwe must first make the file executableand then we can run itchmod + hello py /hello py we need to run the chmod command only once of courseafter that we can simply enter /hello py and the program will run on unixwhen program is invoked in the consolethe file' first two bytes are read if these bytes are the ascii characters #!the shell assumes that the file is to be executed by an interpreter and that the file' first line specifies which interpreter to use this line is called the shebang (shell executelineand if present must be the first line in the file the shebang line is commonly written in one of two formseither#!/usr/bin/python or#!/usr/bin/env python if written using the first formthe specified interpreter is used this form may be necessary for python programs that are to be run by web serverthe interaction between the user and the console is handled by "shellprogram the distinction between the console and the shell does not concern us hereso we use the terms interchangeably