Python's import: why doesn't it work?

[djw]

Jurie Horneman wrote:
> Once again my attempt to profit from Python's vaunted productivity
> increase has come to a screeching halt because some innocent thing
> that one would reasonably expect to work in one line, intuitively, and
> without even having to think about, turns into a nightmare already
> lasting more than an hour, requiring numerous experiments, searching
> through the documentation - both manually and using my editor's
> find-in-files - finally leaving me no other option but to write a post
> to comp.lang.python, knowing that my programming flow for today is
> well and truly gone. I hate doing this, because I know I cannot keep
> my frustration out of my writing, and also that someone will reply and
> gently or not so gently point out something which actually IS written
> down in some obscure corner of the documentation, despite my attemps
> to RTFM.
> 
> So, what is it this time? No, it's not Unicode, another aspect that
> frequently trips me up, causing my face to meet the rough asphalt of
> the infobahn. It's importing modules. Again.
> 
> (This is an obscure reference to an attempt on my part to implement
> MBCS conversion functions as Python codecs. This failed miserably and
> despite the helpful advice I received here, I never did try again. Too
> bad, because those conversion functions are pretty good. And since I'm
> doing some parenthesized ranting here: does anyone outside of the
> Python world use 'codec' to refer to anything except audio / video
> codecs? I actually had to post here just to find out that what I was
> looking for were *called* codecs. Sheesh.)
> 
> Anyway.
> 
> I have this script, let's call it 'blah.py'. It sits in a directory
> far, far away from where my Python is installed. It wants to include a
> module called 'intro' from a subdirectory called 'templates'.
> 
> This is evidently impossible.
> 
> Among my vain, futile attempts were:
> 
> *** Solution 1 ***
> The World is a Beautiful Place
> 
> 
>>>>import templates.intro
>>>
> 
> Ha! ha! ha! OK, even I knew this was a bit optimistic.
> 
> *** Solution 2 ***
> .PTH file
> 
> Put a templates.pth containing the single line 'templates' in the same
> place as 'blah.py', then
> 
> 
>>>>import templates.intro
>>>
> or
> 
>>>>import intro
>>>
> 
> No dice: 'ImportError: No module named...' etc.
> 
> *** Solution 3 ***
> IMPorting by hand
> 
> 
>>>>import imp
>>>>f = open('templates\intro.py')
>>>
> 
>>>>imp.find_module('intro.py')
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No module named intro.py
> 
> 
>>>>imp.find_module('intro')
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No module named intro
> 
> 
>>>>imp.find_module('intro', '\\templates\\')
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No frozen submodule named .\templates\.intro
> 
> (No WHAT?)
> 
> 
>>>>imp.find_module('intro', '\\templates\\')
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No frozen submodule named \templates\.intro
> 
> 
>>>>imp.find_module('intro', ['\\templates\\'])
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No module named intro
> 
> 
>>>>imp.find_module('intro.py', ['\\templates\\'])
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No module named intro.py
> 
> 
>>>>imp.find_module('intro', ['.\\templates\\'])
>>>
> (<open file '.\templates\intro.py', mode 'r' at 0x01511110>,
> '.\\templates\\intro.py', ('.py', 'r', 1))
> 
> Whoa! I finally managed to call imp.find_module without raising an
> exception! OK, now to call imp.load_module, because the documentation
> says:
> 
> "Load a module that was previously found by find_module()"
> 
> Alright, so there seems to be some connection between find_module and
> load_module... The latter probably takes the return value of the
> former as a parameter, right? Right? Wrong.
> 
> Here are my attemps to call imp.load_module:
> 
> x = imp.find_module('intro', ['.\\templates\\'])
> 
> 
>>>>y = imp.load_module('intro', f, 'intro.py', x)
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> TypeError: load_module() argument 4, item 0 must be string, not file
> 
> 
>>>>y = imp.load_module('intro', x)
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> TypeError: load_module() takes exactly 4 arguments (2 given)
> 
> Okay, wait, my assumption was obviously naive, better read the doc...
> aha. Almost the same parameters as find_module... wonder why I even
> needed to call find_module in the first place. OK:
> 
> 
>>>>y = imp.load_module('intro', f, 'intro.py', imp.get_suffixes())
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> TypeError: load_module() argument 4 must be sequence of length 3, not
> 5
> 
> What? But... but... *splutter* the doc says:
> 
> "The description argument is a tuple, as would be returned by
> get_suffixes(), describing what kind of module must be loaded."
> 
> So why doesn't this work? OK, I have no idea why I'm bothering with
> these kinds of arcana, but for the heck of it I'll try:
> 
> 
>>>>y = imp.load_module('intro', f, 'intro.py', ('.py', 'r', 1))
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
>   File "intro.py", line 29, in ?
> ImportError: No module named Base
> 
> Yay! What?! Now my IMPORTED module can't find the modules IT is trying
> to import? (It doesn't matter if I put Base next to Blah.py or in
> templates - Intro can't find it.)
> 
> Arrrgghhh!!!! OK, enough time spent on this dead end. (Oh, and by the
> way not all the functions of the imp module are documented.)
> 
> *** Solution 4 ***
> Packages
> 
> OK, more searching, browsing and scouring my hard drive for the word
> 'import'. Of course! I forgot that in the Python docs, important
> information is cunningly hidden in the Tutorial section! (Really, am I
> being unreasonable for assuming that once one has reached a certain
> level of knowledge, one shuns the Tutorial and goes straight for the
> main documentation, because that's where one can find everything there
> is to know? That's only how it works in every language or piece of
> software in general I've ever encountered.)
> 
> So there are these things called 'packages'. Wow! Handy, that! All one
> needs to do is put an empty file called '__init__.py' in a directory,
> and hey! That directory becomes a package and Bob's your uncle.
> 
> So I put an empty file called '__init__.py' in 'templates' and try the
> following:
> 
> 
>>>>import templates.intro
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No module named templates.intro
> 
> 
>>>>from templates import intro
>>>
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> ImportError: No module named templates
> 
> This is *exactly* how it's written in the Tutorial, and
> it-does-not-work.
> 
> *** Solution 5 ***
> Abject Defeat, Ask on Internet, Be Ridiculed by Peers for Not Managing
> Basic Operation
> 
> Amusing little anecdote: I've performed all of the above steps twice -
> once while growing increasingly frustrated, and a second time while
> writing this post. Twice, while typing in the code above, I at some
> point entered:
> 
> import intro
> 
> ... and it would work. For real. The symbols were there. Not a peep
> out of the interpreter.
> 
> Because I don't trust PythonWin (don't get me started on PythonWin, I
> haven't found a better IDE yet, I may actually succumb and PAY for one
> soon *shock horror*) I quit and restarted and lo and behold! the
> interpreter complained that there was no such module, as it had been
> doing all along, the horrible beast.
> 
> In other words, at random, unreproducable moments, Python perversely
> imported my module, whereas normally it refused to.
> 
> To cut a long story... hm... Please please help me! Stop me before I
> whine again. And please don't be offended by my ranting, I just can't
> hide this much frustration. I'm using Python 2.2 by the way.
> 
> Thanks in advance,
> 
> Jurie.

Hmmmm... I think you need to look into the documentation under 
"packages"... this tripped me up too until I figured out this (somewhat) 
unintuitive mechanism to get modules in subdirs to load.

Here's what I did (on a Win2K box) to show you the steps:

1. Create a c:\blah subdir ("far" from Python directory, but doesn't 
really matter)
2. Create a blah.py in c:\blah that contains 1 line:
import templates.intro
3. Create a c:\blah\templates directory
4. Create a blank (empty) file in c:\blah\templates called __init__.py
5. Create a intro.py in c:\blah\templates that contains the line:
print "intro!" # this will print when we successfully import intro.py
6. Run blah.py:

C:\blah>python blah.py
intro!

C:\blah>

BTW, step #4 is the critical piece.

Hope this helps,

Don