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module confusion

Sorry if this is a completely newbie question ...

I was trying to get information about the logging.handler s module, so
I imported logging, and tried dir(logging.han dlers), but got:

AttributeError: 'module' object has no attribute 'handlers'

The only experience I have in modules is os and os.path ... if I do
the same thing, simply import os and then type dir(os.path), it
displays the contents as expected.

So my question is ... why are they different? I mean, in terms of
designing these modules, how would you go about getting a sub-module
in your name space? And on the other side, how would you go about
getting it out?

Thanks!

Oct 2 '07
40 3522
En Wed, 03 Oct 2007 07:12:17 -0300, Lawrence D'Oliveiro
<ld*@geek-central.gen.new _zealandescribi �:
In message <ma************ *************** ***********@pyt hon.org>, Robert
Kern wrote:
>Lawrence D'Oliveiro wrote:
>>In message <ma************ *************** ***********@pyt hon.org>,
Robert
Kern wrote:

Not all of the modules in a package are imported by importing the
top-level package.

You can't import packages, only modules.

os.path is a particularly weird case because it is just an alias to
the
platform-specific path-handling module; os is not a package.

os is a module, os.path is a variable within that module. That's all
there is to it.

Yes, but os.path is also module. That's why I said it was a weird case.

You can't have modules within modules. os.path isn't an exception--see
below.
>In [1]: import os

In [2]: type(os.path)
Out[2]: <type 'module'>

On my Gentoo system:
>>import os
>>os.path
<module 'posixpath' from '/usr/lib64/python2.5/posixpath.pyc'>

It's just a variable that happens to point to the posixpath module.
A "module" is a certain type of Python objects, like ints, functions,
exceptions and all else.
The easiest way to create a module is to load it from file, but some
modules are already built into the interpreter, and you can even create a
module from scratch.

pyimport os
pytype(os)
<type 'module'>
pytype(os.path)
<type 'module'>
pyos
<module 'os' from 'c:\apps\python 25\lib\os.pyc'>
pyimport sys
pytype(sys)
<type 'module'>
pysys
<module 'sys' (built-in)>
pyModuleType = type(os)
pynewmodule = ModuleType('new module')
pynewmodule.a = 3
pynewmodule
<module 'newmodule' (built-in)>
pytype(newmodul e) is type(os.path)
True

"os" is a name that refers to the os module object. "os.path" means "the
path attribute in the object referenced by the name os", that happens to
be another module too.
os is not a package; os.path is set when the os module is imported,
depending on the platform. It may be ntpath, posixpath, macpath, or
whatever. On Windows:

pyimport ntpath
pyos.path is ntpath
True
pyimport macpath
pyimport posixpath
pymacpath.sep
':'
pyntpath.sep
'\\'

Apart from that, there is no magic involved, just plain attribute access
like everywhere else.

--
Gabriel Genellina

Oct 3 '07 #11
Lawrence D'Oliveiro wrote:
In message <ma************ *************** ***********@pyt hon.org>, Robert
Kern wrote:
>Lawrence D'Oliveiro wrote:
>>In message <ma************ *************** ***********@pyt hon.org>, Robert
Kern wrote:

Not all of the modules in a package are imported by importing the
top-level package.
You can't import packages, only modules.

os.path is a particularly weird case because it is just an alias to the
platform-specific path-handling module; os is not a package.
os is a module, os.path is a variable within that module. That's all
there is to it.
Yes, but os.path is also module. That's why I said it was a weird case.

You can't have modules within modules. os.path isn't an exception--see
below.
>In [1]: import os

In [2]: type(os.path)
Out[2]: <type 'module'>

On my Gentoo system:
>>import os
>>os.path
<module 'posixpath' from '/usr/lib64/python2.5/posixpath.pyc'>

It's just a variable that happens to point to the posixpath module.
I believe that is precisely what I was saying.

--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco

Oct 3 '07 #12
+1 Subject line of the week (SLOTW)

rjcarr wrote:
So my question is ... why are they [os.path and logging.handler s] different?
[A] wrote:
Because you misspelled it. First, do a dir() on logging:
[b] wrote:
No, he didn't... OP: logging is a package and logging.handler s is one module
in the package... os.path is a particularly weird case...
[C] wrote:
You can't import packages, only modules.
[D] wrote:
Oh come on, this is unnecessary nitpicking.
[E] wrote:
You *can* import a package, and a package is just a *little* different from a
module
[b] wrote:
Yes, but os.path is also module. That's why I said it was a weird case.
[C] wrote:
You can't have modules within modules. os.path isn't an exception...It' s just
a variable that happens to point to the posixpath module.
[F] wrote:
There's no "pointing" going on. It's another name bound to the same object,
of equal status to the 'posixpath' name.
[G] wrote:
a module is just an object, that can of course be an attribute of another
module object
[H] wrote:
os is not a package; os.path is set when the os module is imported
[C] wrote:
You're right. I was misremembering the behaviour of PyCrypto
[J] wrote:
In Matlab you can use function dec2bin, hex2dec, dec2hex bin2dec functions to
convert decimal to binary and heximal etc.
[b] wrote:
I believe that is precisely what I was saying.

with apologies to all concerned :-)

Michael

Oct 3 '07 #13
In message <87************ @benfinney.id.a u>, Ben Finney wrote:
Lawrence D'Oliveiro <ld*@geek-central.gen.new _zealandwrites:
>On my Gentoo system:
> >>import os
>>os.path
<module 'posixpath' from '/usr/lib64/python2.5/posixpath.pyc'>

It's just a variable that happens to point to the posixpath module.

There's no "pointing" going on. It's another name bound to the same
object, of equal status to the 'posixpath' name.

Python doesn't have pointers, and even "variable" is a misleading term
in Python. Best to stick to "name" and "bound to".
In Python, all names _are_ variables. They are not "bound" to objects. The
value of os.path is a pointer. It's implemented as a pointer, it has all
the semantics of a pointer.

Honestly, why do people react to the word "pointer" as though computers have
to wear underwear to conceal something shameful going on in their nether
regions?
Oct 3 '07 #14
On Thu, 2007-10-04 at 11:11 +1300, Lawrence D'Oliveiro wrote:
In Python, all names _are_ variables. They are not "bound" to objects. The
value of os.path is a pointer.
No. "os.path" refers to the object that's known as the "path" attribute
of the object known as "os". That object, in turn, is a module.
It's implemented as a pointer,
While it is true that namespaces are implemented in CPython as
collections of pointers to PyObject structures, that's an irrelevant
implementation detail. I doubt that they are implemented as pointers in
Jython, PyPy, or IronPython.
it has all the semantics of a pointer.
No, it doesn't. A pointer means the physical address of a memory
location, which implies that you can overwrite that memory location. Can
you do that in Python?
Honestly, why do people react to the word "pointer" as though computers have
to wear underwear to conceal something shameful going on in their nether
regions?
I won't speak for "people", but maybe it's because Python acts precisely
as this underwear that does conceal the low-level regions of memory
management and bit-twiddling that Python programmers like to avoid in
favor of solving higher-level problems.

If it helps you to think of Python names as "kind of like pointers,"
you're free to do so, but it's only a weak analogy that can lead
beginners to drawing incorrect conclusions.

--
Carsten Haese
http://informixdb.sourceforge.net
Oct 4 '07 #15
Lawrence D'Oliveiro wrote:
In message <87************ @benfinney.id.a u>, Ben Finney wrote:
>Lawrence D'Oliveiro <ld*@geek-central.gen.new _zealandwrites:
>>On my Gentoo system:

>>import os
>>os.path
<module 'posixpath' from '/usr/lib64/python2.5/posixpath.pyc'>

It's just a variable that happens to point to the posixpath module.
There's no "pointing" going on. It's another name bound to the same
object, of equal status to the 'posixpath' name.

Python doesn't have pointers, and even "variable" is a misleading term
in Python. Best to stick to "name" and "bound to".

In Python, all names _are_ variables. They are not "bound" to objects. The
value of os.path is a pointer. It's implemented as a pointer, it has all
the semantics of a pointer.

Honestly, why do people react to the word "pointer" as though computers have
to wear underwear to conceal something shameful going on in their nether
regions?
Because they have been told by their church that all God-fearing names
do what names have always done in programming languages, which is to
describe areas of memory of a particular size, type and locality.

You and I know that the semantics of Python names are precisely those of
(to use an Algol 68 term, unless I am mistaken) automatically
dereferenced pointers to objects of arbitrary type. I actually think
that's one of the neatest things about Python, and I believe it's no
accident that both Tim Peters and I were Icon enthusiasts.

But the rest of the world clings to its illusions.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden

Sorry, the dog ate my .sigline

Oct 4 '07 #16
Lawrence D'Oliveiro wrote:
In message <87************ @benfinney.id.a u>, Ben Finney wrote:
>Lawrence D'Oliveiro <ld*@geek-central.gen.new _zealandwrites:
>>On my Gentoo system:

>>import os
>>os.path
<module 'posixpath' from '/usr/lib64/python2.5/posixpath.pyc'>

It's just a variable that happens to point to the posixpath module.
There's no "pointing" going on. It's another name bound to the same
object, of equal status to the 'posixpath' name.

Python doesn't have pointers, and even "variable" is a misleading term
in Python. Best to stick to "name" and "bound to".

In Python, all names _are_ variables. They are not "bound" to objects. The
value of os.path is a pointer. It's implemented as a pointer, it has all
the semantics of a pointer.

Honestly, why do people react to the word "pointer" as though computers have
to wear underwear to conceal something shameful going on in their nether
regions?
Because they have been told by their church that all God-fearing names
do what names have always done in programming languages, which is to
describe areas of memory of a particular size, type and locality.

You and I know that the semantics of Python names are precisely those of
(to use an Algol 68 term, unless I am mistaken) automatically
dereferenced pointers to objects of arbitrary type. I actually think
that's one of the neatest things about Python, and I believe it's no
accident that both Tim Peters and I were Icon enthusiasts.

But the rest of the world clings to its illusions.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden

Sorry, the dog ate my .sigline

Oct 4 '07 #17
Steve Holden <st***@holdenwe b.comwrites:
You and I know that the semantics of Python names are precisely
those of (to use an Algol 68 term, unless I am mistaken)
automatically dereferenced pointers to objects of arbitrary type.
Yes. That's exactly why it's wrong to refer to them as pointers. They
don't behave like the pointers in other languages, which are *not*
"automatica lly-dereferenced", nor "to objects of arbitrary type".

It's misleading to talk about a Python name as a "pointer" without
those qualifiers, because they're *not* implicit in programmers'
understanding of that term.

If you want to continually refer to them as
"automatica lly-dereferenced pointers to objects of arbitrary type", by
all means go ahead. That at least *does* fit the semantics. But the
simple term "pointer" does *not* describe them in the absence of those
necessary and non-default qualifiers, and is misleading.

--
\ "I wish there was a knob on the TV to turn up the intelligence. |
`\ There's a knob called 'brightness' but it doesn't work." -- |
_o__) Eugene P. Gallagher |
Ben Finney
Oct 4 '07 #18
Ben Finney wrote:
Steve Holden <st***@holdenwe b.comwrites:
>You and I know that the semantics of Python names are precisely
those of (to use an Algol 68 term, unless I am mistaken)
automaticall y dereferenced pointers to objects of arbitrary type.

Yes. That's exactly why it's wrong to refer to them as pointers. They
don't behave like the pointers in other languages, which are *not*
"automatica lly-dereferenced", nor "to objects of arbitrary type".

It's misleading to talk about a Python name as a "pointer" without
those qualifiers, because they're *not* implicit in programmers'
understanding of that term.

If you want to continually refer to them as
"automatica lly-dereferenced pointers to objects of arbitrary type", by
all means go ahead. That at least *does* fit the semantics. But the
simple term "pointer" does *not* describe them in the absence of those
necessary and non-default qualifiers, and is misleading.
In practice I am quite happy talking about "variables" as long as nobody
is picking nits, but I am afraid that in this thread the nits are not
only being picked, they are being boiled alive and eaten.

Consequently I feel obliged to reply in my own defense that if you
weren't intelligent enough to recognize that description as essentially
correct this conversation need have gone no further. I don't encourage
people to talk in terms of pointers most of the time, but I find that
such pedagogic devices are useful in discussing the essential
differences between mutable and immutable values.

Neither do I normally attempt to mislead (as an examination of my record
on this group should confirm), which is precisely why the qualifiers
*were* attached. So kindly do not tell me it's "wrong" to refer them as
pointers. Such phraseology can tend to be emotionally charged (for
instance when proponents have religious feelings about their beliefs).

Fortunately programming languages and operating systems have never been
religious issues for me. It's more like "This problem has a cross head,
so I'll need a Philips screwdriver". I don't worship my spirit level, so
I'm damned if I will worship LISP or Python. They can both be *jolly*
useful, though

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden

Sorry, the dog ate my .sigline so I couldn't cat it

Oct 4 '07 #19
In message <ma************ *************** ***********@pyt hon.org>, Carsten
Haese wrote:
On Thu, 2007-10-04 at 11:11 +1300, Lawrence D'Oliveiro wrote:
>In Python, all names _are_ variables. They are not "bound" to objects.
The value of os.path is a pointer.

No. "os.path" refers to the object that's known as the "path" attribute
of the object known as "os". That object, in turn, is a module.
No, it's a variable. It just happens to contain a pointer to a module.
> It's implemented as a pointer,

While it is true that namespaces are implemented in CPython as
collections of pointers to PyObject structures, that's an irrelevant
implementation detail. I doubt that they are implemented as pointers in
Jython, PyPy, or IronPython.
I'll bet they are.
> it has all the semantics of a pointer.

No, it doesn't. A pointer means the physical address of a memory
location, which implies that you can overwrite that memory location. Can
you do that in Python?
Yes. Look up the definition of "mutable objects".

Oct 4 '07 #20

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