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

[dsavitsk]

"Jurie Horneman" <jhorneman at pobox.com> wrote in message
news:9ac02e81.0209290839.4f4d6475 at posting.google.com...
> 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.


So, I would like to agree that, while in MS world this would be called a
feature of some sort, that it is either a design flaw in Python, or a major
oversight in the documentation.  I have had most of the same frustration as
the poster, and usually stumbled onto something that worked (which too many
times sees to have involved \Lib\) Perhaps someone should write a "Complete
Guide to Importing Modules" -- maybe it's in the new Nutshell Book -- which
I would do if I understood it?

(Too add another complaint to the above, as well, Python used in active
server pages does not see .pth files forcing sys.append() as the first line
of each.)

-d