Page - 118 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Volume Second Edition

118 5 SomeMorePythonEssentials WheretoPlacea ModuleFile? For a module import to be successful, a first requirement is that Python can find themodulefile.Asimplewaytomakethishappen, is toplacethemodule filein thesamefolderastheprogram(that tries to import themodule).a There areotheralternatives,but thenyoushouldknowhowPythonlooksformodule files. When Python proceeds to import a module, it looks for the module file within the folders contained in the sys.path list. To see the folders in sys.path,wemaydo: In [1]: import sys In [2]: sys.path Out[2]: [’’, ’/.../.../site-packages/spyder/utils/site’, ... ... < longer printout... author’s comment > ... ’/.../.../site-packages/IPython/extensions’, ’/.../.../.ipython’] Placingyourmodule inoneof the folders listed, assures thatPythonwill find it. If, for some reason, you want to place your module in a folder that is not listed insys.path, you may insert that folder name insys.path. With our sys.pathhere,wecould insert thefoldernamemy_folder, forexample,by continuingour sessionas In [3]: sys.path.insert(0, ’my_folder’) # 0 - location in sys.path In [2]: sys.path Out[2]: [’my_folder’, ’’, ’/.../.../site-packages/spyder/utils/site’, ... ... ... ’/.../.../site-packages/IPython/extensions’, ’/.../.../.ipython’] The first argument toinsertgives the location in thesys.path list where you want the folder name to be inserted (0 gives first place, 1 gives second, andso on). You may also use the PYTHONPATH variable (https://docs.python.org/3/ using/cmdline.html#envvar-PYTHONPATH),but theaboveshouldsufficefor abeginner. Ifyouwanttorunyourmodulefilealsoasaprogram,thelocationofthefile might require that you first update the PATH environmentvariable (see, e.g., http://hplgit.github.io/primer.html/doc/pub/input/._input-readable009.html). a In thisbook, we keep to this simple way.***