Move from Excel to Python with Pandas Transcripts
Chapter: Appendix: Python language concepts
Lecture: Concept: Imports and importing modules

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0:01 Packages and modules must be imported in Python before they can be used.
0:06 It doesn't matter if it's in external package of the package index,
0:09 in module from the standard library or even a module or package
0:12 you yourself have created, you have to import it.
0:16 So code as it's written right here likely will not work,
0:20 you will get some kind of NameError, "os doesn't exist, path doesn't exist".
0:23 That's because the os module and the path method contained within it have not been imported.
0:29 So we have to write one of two statements above,
0:33 don't write them both, one or the other.
0:35 So, the top one lets us import the module and retains the namespace,
0:39 so that we can write style one below, so here we would say os.path.exist
0:44 so you know that the path method is coming out of the os module.
0:47 Alternatively, if you don't want to continue repeat os.this, os.that,
0:52 and you just want to say "path", you can do that by saying this other style,
0:56 from os import path.
0:58 And then you don't have to use the namespace,
1:00 you might do this for method used very commonly
1:02 whereas you might use style one for methods that are less frequently used.
1:07 Now, there is the third style here, where we could write "from os import *",
1:10 that means just like the line above, where we are importing path,
1:14 but in fact, import everything in the os module.
1:17 You are strongly advised to stay away from this format
1:19 unless you really know what you are doing, this style will import and replace
1:24 anything in your current namespace that happens to come out of the os.
1:28 So for example, if you had some function that was called register,
1:33 and maybe there is a register method inside os module,
1:37 this import might erase your implementation, depending where it comes from.
1:41 So, modules must be imported before you use them,
1:44 I would say prefer to use the namespace style, it's more explicit
1:48 on where path actually comes from,
1:50 you are certain that this is the path from the os module,
1:52 not a different method that you wrote somewhere else
1:54 and it just happens to have the same name.
1:56 Style two also works well, style three- not so much.