append to non-existing list

[Yves Glodt]

Hello,

if I do this:

for row in sqlsth:
________pkcolum ns.append(row[0].strip())
________etc
without a prior:

pkcolumns = [];
I get this error on first iteration:
UnboundLocalErr or: local variable 'pkcolums' referenced before assignment

I guess that's normal as it's the way python works...?!?

My question is: Is there no way to append to a non existing list?

I am lazy for declaring it first, IMHO it bloats the code, and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...
regards,
Yves

[dcrespo]

Hi

I think there's no way to append to a non existing list.

Sorry about my question, but the English is my second language, and I
don't know what is the meaning of IHMO (or IMHO). I googled and found
that it means "In My Humbled Opinion", is that true? Thanks and accept
my appologies for not talking entirely about your problem.

Daniel

[bonono]

I am afraid you have to either go back to php or whatever programming
language that fits your style or change your style to fit python.

There is a lot I don't like about python but if you have to use it, you
have to cope with it.

Yves Glodt wrote:

My question is: Is there no way to append to a non existing list?

I am lazy for declaring it first, IMHO it bloats the code, and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...
regards,
Yves

[Juho Schultz]

Yves Glodt wrote:

Hello,

if I do this:

for row in sqlsth:
________pkcolum ns.append(row[0].strip())
________etc
without a prior:

pkcolumns = [];
I get this error on first iteration:
UnboundLocalErr or: local variable 'pkcolums' referenced before assignment

I guess that's normal as it's the way python works...?!?

My question is: Is there no way to append to a non existing list?

I am lazy for declaring it first, IMHO it bloats the code, and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...
regards,
Yves

You mean you want to type "pkcolumns" only once to keep your code short?
Would something like this be useful?

pkcolumns = [row.strip() for row in sqlsth]

[bonono]

Juho Schultz wrote:

Yves Glodt wrote:

Hello,

if I do this:

for row in sqlsth:
________pkcolum ns.append(row[0].strip())
________etc

You mean you want to type "pkcolumns" only once to keep your code short?
Would something like this be useful?

pkcolumns = [row.strip() for row in sqlsth]

I don't think this is the same as his original code though. There is an
"etc" there. Your version is cleaner and easier to understand but it
can mean another extra pass to go through the result and if sqlsth is
an iterable, it needs to be saved away before iterating it.

[Yves Glodt]

bo****@gmail.co m wrote:

I am afraid you have to either go back to php or whatever programming
language that fits your style or change your style to fit python.
sorry for offending... I just asked a question, and now I know one more
thing about python...

And btw I really am surprised by the amount of answers that my question
rose, in so little time!

thanks all!
There is a lot I don't like about python but if you have to use it, you
have to cope with it.

Yves Glodt wrote:

My question is: Is there no way to append to a non existing list?

I am lazy for declaring it first, IMHO it bloats the code, and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...
regards,
Yves

[Yves Glodt]

Juho Schultz wrote:

Yves Glodt wrote:

Hello,

if I do this:

for row in sqlsth:
________pkcolum ns.append(row[0].strip())
________etc
without a prior:

pkcolumns = [];
I get this error on first iteration:
UnboundLocalErr or: local variable 'pkcolums' referenced before assignment

I guess that's normal as it's the way python works...?!?

My question is: Is there no way to append to a non existing list?

I am lazy for declaring it first, IMHO it bloats the code, and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...
regards,
Yves

You mean you want to type "pkcolumns" only once to keep your code short?
Would something like this be useful?

pkcolumns = [row.strip() for row in sqlsth]

I will look into this, maybe it's what I need, thanks!

[bruno at modulix]

Yves Glodt wrote:

Hello,

if I do this:

for row in sqlsth:
________pkcolum ns.append(row[0].strip())
________etc
without a prior:

pkcolumns = [];
I get this error on first iteration:
UnboundLocalErr or: local variable 'pkcolums' referenced before assignment

I guess that's normal as it's the way python works...?!?
yes sir.
My question is: Is there no way to append to a non existing list?
No. Definitively. And that's a Good Thing(tm).

How would you use something that doesn't exist ???
I am lazy for declaring it first,
s/declaring/instantiating/

If you were to use your own class Toto, would you ever hope that the
following code would work :

for v in some_seq:
toto.dothis(v)

without instantiating Toto and binding it to the name 'toto' before ?
Well, in Python, a list is an instance of class list. There are
syntactic sugar to instanciate a list (or a tuple or a string or a dict
etc), but this:

my_list = []

is strictly equivalent to this:

my_list = list()

Now let's try something else:

class Machin(object):
def append(self, value): pass

class Bidule(object):
def append(self, value): pass

for i in range(10):
m.append(i)
How should Python interpret this ? Should it create a list, or a Machin,
or a Bidule, or an instance of whatever imported class having a
append() method ?
IMHO it bloats the code,
run your python interpreter and type:
import this

Then read carefully.

Now if being explicit still hurts your personal convictions, there's
this other language with a name starting with p... !-)
and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...

Not creating an Array before using it is Bad Style in PHP (and generate
a Warning BTW).

There are warts in Python (as in any other languages), and there are
things that sometimes bore me but are not really warts. But having to
explicitely instanciate objects can't be seen as a wart in any language
IMHO !-)

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

[Thomas Bellman]

Yves Glodt <y.*****@sitaso ftware.lu> writes:

I guess that's normal as it's the way python works...?!?
Yes, that's the way Python works.
My question is: Is there no way to append to a non existing list?
The next time you go shopping at your local super-market, do
*not* get a shopping-cart (or shopping-basket, or any similar
container). As you pick up the things you want to buy, try
to put them into the non-existing cart. Perhaps you will then
become enlightened.
I am lazy for declaring it first, IMHO it bloats the code, and (don't
know if it's good to say that here) where I come from (php) I was used
to not-needing it...

Basically you want Python to automatically create a list out of
nowhere and bind a variable to that list when you try to access
a variable that doesn't exist in a certain way. How do you
propose that Python should now that it is a *list* you want, and
not some other kind of object?
There actually is a way to do what you want:

for row in sqlsth:
try:
pkcolumns.appen d(row[0].strip())
except NameError:
pkcolumns = [ row[0].strip() ]

However, as you see it is much more work than to do it the right
way. It's also much more fragile; think for example about what
happens if your SQL statement (I assume that's what sqlsth is)
yields zero rows, and you then try to look at pkcolumns after
that loop.
--
Thomas Bellman, Lysator Computer Club, Linköping University, Sweden
"God is real, but Jesus is an integer." ! bellman @ lysator.liu.se
! Make Love -- Nicht Wahr!

[bonono]

Thomas Bellman wrote:

The next time you go shopping at your local super-market, do
*not* get a shopping-cart (or shopping-basket, or any similar
container). As you pick up the things you want to buy, try
to put them into the non-existing cart. Perhaps you will then
become enlightened.

But in PHP(and I believe Perl), it is more like :

"oops, I need a cart. <shout>Hello, I need a cart here, please" and
magically, someone wheel you a cart which you can put your stuff in.
The "@" is the magic calls for service. So as a customer, this sounds
like better service but that will create problems to the super market
as it need extra staff for this service and the environment is noiser,
that is another story.