[Tutor] Fwd: question 1

[Danny Yoo]

Forwarding response to tutor; didn't realize it was only sent to me.



---------- Forwarded message ----------
From: Danny Yoo <dyoo at hashcollision.org>
Date: Sun, Sep 21, 2014 at 3:10 PM
Subject: Re: [Tutor] question 1
To: Clayton Kirkwood <crk at godblessthe.us>


On Sun, Sep 21, 2014 at 2:42 PM, Clayton Kirkwood <crk at godblessthe.us> wrote:
>> Secondarily, why can you import a module without it importing all of
>> its daughters?
>
> The act of importing a module is "recursive": if you import a module, and that module itself has import statements, then Python will do the import of the child modules too.  And so forth.
>> And why do you have to use a ‘for in to import submodule’, why not
>> ’import module.sub’?
>
> If I'm not mistaken, you _can_ do this.  Can you point us to a source where it says you can't?
>
> (There are particular style guidelines from certain organizations that prohibit this kind of import, but that prohibition is by convention.
> That is, it's not because the language disallows it, but because it doesn't fit with the house coding style.)
>
>
> [Clayton Kirkwood]
> From the interpreter:
>
> import io
> import io.FileIO
> Traceback (most recent call last):
>   File "<string>", line 1, in <fragment>
> builtins.ImportError: No module named 'io.FileIO'; 'io' is not a package


Hi Clayton,

Ah.  But 'FileIO' is not a module.  It's a value in the 'io' module.
We can see this here:

#######################################################
dhcp-9:work dyoo$ python
Python 2.7.5 (default, Mar  9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import io
>>> io
<module 'io' from
'/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/io.pyc'>
>>> io.FileIO
<type '_io.FileIO'>
#######################################################

When we say:

    import xxx

then the "xxx" has to be a module.


The 'from/import' statement is deceptively named, unfortunately; it's
doing a little more than just module import.

    https://docs.python.org/2/tutorial/modules.html#more-on-modules

where when we say:

   from xxx import yyy

then xxx.yyy could be a module, or it might not.  The act of module
import is involved, so in a sense, the statement is doing an import.
But the 'yyy' doesn't have to be a module.

When we say:

   from io import FileIO

we are taking a value from the 'io' module, and giving it the name 'FileIO



So yeah, it's a little confusing.  For that reason, certain style
guidelines have a say when something is appropriate to write, apart
from what Python technically allows.  As a concrete example, see:

    https://google-styleguide.googlecode.com/svn/trunk/pyguide.html?showone=Imports#Imports

Here, we see a style decision that is _more_ restrictive than what the
Python language allows.



> Huh.  Can you point to a reference?  Note that third-party documentation (and official documentation!) might be buggy or weird.
> :P  If you can point us to an example, maybe one of us can investigate what's going on there.
> [Clayton Kirkwood]
>
>
> Example from ' http://www.tutorialspoint.com/python/python_files_io.htm'
>
> #!/usr/bin/python
>
> str = raw_input("Enter your input: ");
> print "Received input is : ", str


Just because something is on the web (or email) doesn't mean it's
correct or prefect.

:)

--

There are a few small problems with this example from tutorialspoint:

1.  The semicolon is superfluous.

Take it out: it will still work.


2.  The name 'str' is already a built-in,

    https://docs.python.org/2/library/functions.html#str

so the code here is shadowing the built-in.

In such a small test program, this is fine.  In a real program, I'd
ding this for readability issues.