Bizzare lst length problem

[Ben]

Hello...hopeful ly my last question :-)

I ave a dictionary, where each value is a class instance. I access it
using:

for k, v in self.panels.pan el_list.items() :
print "Number:\t",v.n umber
print "Level:\t",v.le vel
print "Location:\t",v .location
print "MOPS:\t",v.mop s
print "List length:\t",len( v.mops)
print "Matrix:\t",v.m atrix,"\n\n"

The output from this would be (for a given key value):
Number: 181
Level: ovride+supvis
Location: mons=4 v8.0 3rd floor
MOPS: ['287', '288', '289', '290']
List Length: 28
Matrix: kng

This is really odd...my len(v.mops) ought to return 4 (4 elements in
the list). In fact it returns 28. looking at outputs from lots of
records, it seems that the length is almost always 7 time too great
(28/7=4)....but not always. This is really confusing...can anyon
suggest what is going on?

I've been trying to output the list elements as a string with equally
limmited success, but the thing seems so simple I can't see where the
prblem might lie....

Cheers,

Ben

[Fredrik Lundh]

Re: Bizzare lst length problem

Ben wrote:

The output from this would be (for a given key value):
Number: 181
Level: ovride+supvis
Location: mons=4 v8.0 3rd floor
MOPS: ['287', '288', '289', '290']
List Length: 28
Matrix: kng
>
This is really odd...my len(v.mops) ought to return 4 (4 elements in
the list).

adding a

print type(v.mops), repr(v.mops)

debug statement might provide you with the clues you need.

In fact it returns 28. looking at outputs from lots of
records, it seems that the length is almost always 7 time too great
(28/7=4)....but not always.

>>len("['287',")

7

>>len(" '288',")

7

>>len(" '289',")

7

>>len(" '290']")

7

</F>

[Ben]

Re: Bizzare lst length problem

Ah... my list is a string. That explains the len() results, but not why
it is a string in the dirst place.

I have a dictionary containing a number of instances of the following
class as values:

class panel:
mops =[]

def __init__(self,n umber,level,loc ation,mops,matr ix):
self.number=num ber
self.level=leve l
self.location=l ocation
self.mops=mops
self.matrix=mat rix


abve mops is a list, yet when I access it it is a string...



Fredrik Lundh wrote:

Ben wrote:
>

The output from this would be (for a given key value):
Number: 181
Level: ovride+supvis
Location: mons=4 v8.0 3rd floor
MOPS: ['287', '288', '289', '290']
List Length: 28
Matrix: kng

This is really odd...my len(v.mops) ought to return 4 (4 elements in
the list).

>
adding a
>
print type(v.mops), repr(v.mops)
>
debug statement might provide you with the clues you need.
>

In fact it returns 28. looking at outputs from lots of
records, it seems that the length is almost always 7 time too great
(28/7=4)....but not always.

>

>>len("['287',")

7

>>len(" '288',")

7

>>len(" '289',")

7

>>len(" '290']")

7
>
</F>

[Ben]

Re: Bizzare lst length problem

....and when I print out the string, it is still formatted as one would
expect a list to be:

<type 'str'"['01', '02', '03', '04']"



Ben wrote:

Ah... my list is a string. That explains the len() results, but not why
it is a string in the dirst place.
>
I have a dictionary containing a number of instances of the following
class as values:
>
class panel:
mops =[]
>
def __init__(self,n umber,level,loc ation,mops,matr ix):
self.number=num ber
self.level=leve l
self.location=l ocation
self.mops=mops
self.matrix=mat rix
>
>
abve mops is a list, yet when I access it it is a string...
>
>
>
Fredrik Lundh wrote:

Ben wrote:

The output from this would be (for a given key value):
Number: 181
Level: ovride+supvis
Location: mons=4 v8.0 3rd floor
MOPS: ['287', '288', '289', '290']
List Length: 28
Matrix: kng
>
This is really odd...my len(v.mops) ought to return 4 (4 elements in
the list).

adding a

print type(v.mops), repr(v.mops)

debug statement might provide you with the clues you need.

In fact it returns 28. looking at outputs from lots of
records, it seems that the length is almost always 7 time too great
(28/7=4)....but not always.

>>len("['287',")

7

>>len(" '288',")

7

>>len(" '289',")

7

>>len(" '290']")

7

</F>

[John Machin]

Re: Bizzare lst length problem


Ben wrote:

Ah... my list is a string. That explains the len() results, but not why
it is a string in the dirst place.
>
I have a dictionary containing a number of instances of the following
class as values:
>
class panel:
mops =[]
>
def __init__(self,n umber,level,loc ation,mops,matr ix):
self.number=num ber
self.level=leve l
self.location=l ocation
self.mops=mops
self.matrix=mat rix
>
>
abve mops is a list, yet when I access it it is a string...
>

Well, if you are going to spare us from reading all of your code,
you'll have to debug it yourself. The clue that Fredrik gave you is
*not* of the use-once-and-discard variety -- when you are having
problems with the pixies changing your lists into strings, you need to
sprinkle prints of type(pixie_prey ) and repr(pixie_prey ) at salient
points in your code; as first statement in that __init__ method would
be a good start.

[John Machin]

Re: Bizzare lst length problem


Ben wrote:

Ah... my list is a string. That explains the len() results, but not why
it is a string in the dirst place.
>
I have a dictionary containing a number of instances of the following
class as values:
>
class panel:
mops =[]
>
def __init__(self,n umber,level,loc ation,mops,matr ix):
self.number=num ber
self.level=leve l
self.location=l ocation
self.mops=mops
self.matrix=mat rix
>
>
abve mops is a list, yet when I access it it is a string...
>

Well, if you are going to spare us from reading all of your code,
you'll have to debug it yourself. The clue that Fredrik gave you is
*not* of the use-once-and-discard variety -- when you are having
problems with the pixies changing your lists into strings, you need to
sprinkle prints of type(pixie_prey ) and repr(pixie_prey ) at salient
points in your code; as first statement in that __init__ method would
be a good start.

[Ben]

Re: Bizzare lst length problem

Thanks for the advice - I'm already doing just that, so hopefully will
soon be sorted :-p


John Machin wrote:

Ben wrote:

Ah... my list is a string. That explains the len() results, but not why
it is a string in the dirst place.

I have a dictionary containing a number of instances of the following
class as values:

class panel:
mops =[]

def __init__(self,n umber,level,loc ation,mops,matr ix):
self.number=num ber
self.level=leve l
self.location=l ocation
self.mops=mops
self.matrix=mat rix


abve mops is a list, yet when I access it it is a string...

>
Well, if you are going to spare us from reading all of your code,
you'll have to debug it yourself. The clue that Fredrik gave you is
*not* of the use-once-and-discard variety -- when you are having
problems with the pixies changing your lists into strings, you need to
sprinkle prints of type(pixie_prey ) and repr(pixie_prey ) at salient
points in your code; as first statement in that __init__ method would
be a good start.

[John Machin]

Re: Bizzare lst length problem


Ben wrote:

...and when I print out the string, it is still formatted as one would
expect a list to be:
>
<type 'str'"['01', '02', '03', '04']"
>

We know that. Fredrik deduced it and told you well over an hour ago.

Show us the code that is creating instances of the panel class ...

panel1 =
panel(number=?, level=?,locatio n=?,mops=?????? ??????????,matr ix=?)
What are you passing as the 4th positional arg
^^^^^^^^^^^^^^^ ^^^^^^^^ ???

[Ben]

Re: Bizzare lst length problem

Using Fredericks advice I managed to track down the problem - it was
really very stupid. I had accidentally cast the list to a string
earlier in another part of the code. Its a bit of an anticlimax really
- not mysterious at all (just mysteriously remiss on my part)

Apologies for not simple posting the entire code earlier on - but
thanks for everyone for puttin up with me, and in particular to
Frederick for his very useful hint :-)

Cheers,

Ben


John Machin wrote:

Ben wrote:

...and when I print out the string, it is still formatted as one would
expect a list to be:

<type 'str'"['01', '02', '03', '04']"

>
We know that. Fredrik deduced it and told you well over an hour ago.
>
Show us the code that is creating instances of the panel class ...
>
panel1 =
panel(number=?, level=?,locatio n=?,mops=?????? ??????????,matr ix=?)
What are you passing as the 4th positional arg
^^^^^^^^^^^^^^^ ^^^^^^^^ ???

[Theerasak Photha]

Re: Bizzare lst length problem

On 8 Oct 2006 06:12:48 -0700, John Machin <sjmachin@lexic on.netwrote:

>
Show us the code that is creating instances of the panel class ...
>
panel1 =
panel(number=?, level=?,locatio n=?,mops=?????? ??????????,matr ix=?)
What are you passing as the 4th positional arg
^^^^^^^^^^^^^^^ ^^^^^^^^ ???

This is wholly unnecessary.

-- Theerasak

[John Machin]

Re: Bizzare lst length problem


Theerasak Photha wrote:

On 8 Oct 2006 06:12:48 -0700, John Machin <sjmachin@lexic on.netwrote:
>

Show us the code that is creating instances of the panel class ...

panel1 =
panel(number=?, level=?,locatio n=?,mops=?????? ??????????,matr ix=?)
What are you passing as the 4th positional arg
^^^^^^^^^^^^^^^ ^^^^^^^^ ???

>
This is wholly unnecessary.
>
-- Theerasak

What is wholly unnecessary?

[Ben]

Re: Bizzare lst length problem

Ah - I found out why I had cast it to a string. I had not, at that
point, worked out ho to pass the list by value rather than reference,
and so was casting to a string as a stopgap measure that I then forgot
about. Now the problem is fixed after this group told me how to pass a
list by value (by slicing the entire list)


John Machin wrote:

Theerasak Photha wrote:

On 8 Oct 2006 06:12:48 -0700, John Machin <sjmachin@lexic on.netwrote:

>
Show us the code that is creating instances of the panel class ...
>
panel1 =
panel(number=?, level=?,locatio n=?,mops=?????? ??????????,matr ix=?)
What are you passing as the 4th positional arg
^^^^^^^^^^^^^^^ ^^^^^^^^ ???

This is wholly unnecessary.

-- Theerasak

>
>
What is wholly unnecessary?

[Fredrik Lundh]

Re: Bizzare lst length problem

Ben wrote:

Ah - I found out why I had cast it to a string. I had not, at that
point, worked out ho to pass the list by value rather than reference,
and so was casting to a string as a stopgap measure that I then forgot
about. Now the problem is fixed after this group told me how to pass a
list by value (by slicing the entire list)

if you write code that needs to treat a list as a distinct mutable
value, make sure *your* code makes a copy. relying on the caller to
remember to do that in all cases is way too error prone.

in other words, instead of doing

def function(seq):
# modify the sequence

...

# must pass in a copy, or things will break in mysterious ways
function(list(m ylist))

do

def function(seq):
seq = list(seq) # make a distinct copy
# modify the sequence

...

function(seq)

</F>

[John Machin]

Re: Bizzare lst length problem


Ben wrote:

Ah - I found out why I had cast it to a string. I had not, at that
point, worked out ho to pass the list by value rather than reference,
and so was casting to a string as a stopgap measure that I then forgot
about. Now the problem is fixed after this group told me how to pass a
list by value (by slicing the entire list)
>

All argument passing is by reference. What you are calling "pass a list
by value" is actually two steps:

(1) make a copy of a list
(2) pass a reference to the copy

At the C implementation level, it's a (PyObject *) -- the address of
the object.

HTH,
John

[Bruno Desthuilliers]

Re: Bizzare lst length problem

Ben wrote:

Ah... my list is a string. That explains the len() results, but not why
it is a string in the dirst place.
>
I have a dictionary containing a number of instances of the following
class as values:
>
class panel:
mops =[]

This one is a class attribute - it's shared between all instances of panel.

def __init__(self,n umber,level,loc ation,mops,matr ix):
self.number=num ber
self.level=leve l
self.location=l ocation
self.mops=mops

And here, you create an instance attribute with the same name, that will
shadow the class attribute.

self.matrix=mat rix
>
>
abve mops is a list, yet when I access it it is a string...

the class attribute 'mops' is a list. The instance attribute 'mops' is
whatever you passed when instanciating panel.


--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"