user input and error handling """return true if = within the tolerance ""return abs( btolerance success float_eq(a_computedaand float_eq( _computeda and float_eq(p_computedpand float_eq(n_computednassert success could add message here if desired if __name__ ='__main__'test_all_functions(since we have followed the naming convention of test functionsthe function will be called if we runfor instancepytest interest pybut since we call it from inside the test blockthe test can also be run simply by python interest py in the latter casethe test will produce no output unless there are errors howeverif we import the module to use in another programthe test function is not runbecause the variable __name__ will be the name of the module ( interestand the test __name__ ='__main__will be evaluated as false how python finds our new module python has number of designated places where it looks for modules the first place it looks is in the same folder as the main programthereforeif we put our module files therethey will always be found howeverthis is not very convenient if we write more general modules that we plan to use from several other programs such modules can be put in designated directorysay /users/sundnes/lib/python/mymods or any other directory name that you choose then we need to tell python to look for modules in this directoryotherwiseit will not find the module on unix-like systems (linuxmacetc )the standard way to tell python where to look is by editing the environment variable called pythonpath environment variables are variables that hold important information used by the operating systemand pythonpath is used to specify the folders where python should look for modules if you type echo $pythonpath in the terminal windowyou will most likely obtain no outputsince you have not added any folder names to this variable we can put our new folder name in this variable by running the command terminal export pythonpath=/users/sundnes/lib/python/mymods howeverif the pythonpath already contained any foldersthese will now be lostthereforeto be on the safe sideit is better to use terminal export pythonpath=$pythonpath:/users/sundnes/lib/python/mymods this last command will simply add our new folder to the end of what is already in our pythonpath variable to avoid having to run this command