Linq to Python

[hrishy]

Hi

Will LINQ be ported to Python ?

regards
Hrishy

[Diez B. Roggisch]

Re: Linq to Python

hrishy wrote:

Hi
>
Will LINQ be ported to Python ?

Take a look at SQLAlchemy or SQLObject for python-based
ORM/SQL-abstractions.

Apart from that, python is already heavily based on concepts like iterators,
filtering. Take a look at itertools.

Diez

[Jason Scheirer]

Re: Linq to Python

On Sep 23, 7:48 am, hrishy <hris...@yahoo. co.ukwrote:

Hi
>
Will LINQ be ported to Python ?
>
regards
Hrishy

I think this question is more appropriate to ask on an IronPython
development list -- LINQ is pretty solidly intertwined with .Net, and
so you'll likely want to look at the .Net implementation of Python.

[namekuseijin]

Re: Linq to Python

On Sep 23, 2:07 pm, Jason Scheirer <jason.schei... @gmail.comwrote :

On Sep 23, 7:48 am, hrishy <hris...@yahoo. co.ukwrote:
>

Hi

>

Will LINQ be ported to Python ?

>

regards
Hrishy

>
I think this question is more appropriate to ask on an IronPython
development list -- LINQ is pretty solidly intertwined with .Net, and
so you'll likely want to look at the .Net implementation of Python.

But surely the idea behind it will eventually spread. It's really
just comprehensions generalized over XML and relational datasets, a
noble goal. Besides, it's main purpose for .NET was to bring
functional programming to it. Python already has that, somewhat...

[Thomas G. Willis]

Re: Linq to Python

But surely the idea behind it will eventually spread.  It's really
just comprehensions generalized over XML and relational datasets, a
noble goal.  Besides, it's main purpose for .NET was to bring
functional programming to it.  Python already has that, somewhat...

it's really any object out of the box, i think the sql linq stuff is
more of a query compiler, IMO sqlalchemy does that.


query = select(user_col s,

and_(table_rela tionship.c.acce pt_user_id==use r.id,

table_relations hip.c.start_dat e==None

),

from_obj=join(

table_relations hip,table_user,

onclause=table_ user.c.id==tabl e_relationship. c.init_user_id

).outerjoin(tab le_profile)

)

session.execute (query).fetchal l()






XML? meh hopefully I would never need it. :)


C# is my day job, and when I got my hands on LINQ back in January my
initial thought was "Finally I have list comprehensions! !!! day job is
fun again"

For the most part, I think C# is catching up.

[sturlamolden]

Re: Linq to Python

On Sep 23, 4:48 pm, hrishy <hris...@yahoo. co.ukwrote:

Will LINQ be ported to Python ?

No, because Python already has list comprehensions and we don't need
the XML buzzword.

[bearophileHUGS@lycos.com]

Re: Linq to Python

sturlamolden:

>No, because Python already has list comprehensions and we don't need the XML buzzword.<

LINQ is more than buzzwords. Python misses several of those features.
So maybe for once the Python crowd may recognize such C# feature as
much better than things present in Python.
Said that, I presume Python will go on as usual, and LINQ-like
capabilities will not be integrated in Python. In the meantime where I
live lot of people will keep using C# instead of Python and CLisp,
natural selection at work indeed.

Bye,
bearophile

[Tim Golden]

Re: Linq to Python

bearophileHUGS@ lycos.com wrote:

sturlamolden:

>No, because Python already has list comprehensions and we don't need the XML buzzword.<

>
LINQ is more than buzzwords. Python misses several of those features.
So maybe for once the Python crowd may recognize such C# feature as
much better than things present in Python.
Said that, I presume Python will go on as usual, and LINQ-like
capabilities will not be integrated in Python. In the meantime where I
live lot of people will keep using C# instead of Python and CLisp,
natural selection at work indeed.

Perhaps a quick summary of what LINQ offers which might
"be integrated into Python" would help those of us who
are ignorant? (This is a serious comment; I'd like to know).

TJG

[Chris Mellon]

Re: Linq to Python

On Wed, Sep 24, 2008 at 2:11 PM, <bearophileHUGS @lycos.comwrote :

sturlamolden:

>>No, because Python already has list comprehensions and we don't need the XML buzzword.<

>
LINQ is more than buzzwords. Python misses several of those features.
So maybe for once the Python crowd may recognize such C# feature as
much better than things present in Python.
Said that, I presume Python will go on as usual, and LINQ-like
capabilities will not be integrated in Python. In the meantime where I
live lot of people will keep using C# instead of Python and CLisp,
natural selection at work indeed.
>

Why do you swing so widely between being an interesting poster with
interesting, useful things to say and mindless trolling? There's a lot
of reasons to use C# instead of Python or Lisp (or any other language
for that matter), but I can't imagine that someone would make that
decision based solely on LINQ. I'd go so far as to say that if they
do, I question their professional competence.

LINQ is an interesting implementation of an old idea. The place where
it differs from list comps is that it has appropriate hooks for the
specific linq implementation to override the way results are gathered,
and such hooks in Python would be an interesting idea. I've taken a
shot and figuring out where and how they should be implemented, but I
haven't come up with anything I like. Maybe you should try it?

LINQs "native" object API (not the syntax sugar available in C#) is
not very different from Python ORMs.

[r0g]

Re: Linq to Python

bearophileHUGS@ lycos.com wrote:

sturlamolden:

>No, because Python already has list comprehensions and we don't need the XML buzzword.<

>
LINQ is more than buzzwords. Python misses several of those features.
So maybe for once the Python crowd may recognize such C# feature as
much better than things present in Python.
Said that, I presume Python will go on as usual, and LINQ-like
capabilities will not be integrated in Python. In the meantime where I
live lot of people will keep using C# instead of Python and CLisp,
natural selection at work indeed.
>
Bye,
bearophile

LOL, I just read that and thought - Ok this sounds serious I'd better go
find out what this LINQ business is all about so I googled.. and ended
up on MSDN where there's impressive sounding talk about how we need a
way to query databases and XML files with a unified syntax like we do
for for standard datatypes like files and arrays. Well yes,that makes
sense I think and proceed to look at their example code, curious as to
what this new paradigm looks like:

using System;
using System.Linq;
using System.Collecti ons.Generic;

class app {
static void Main() {
string[] names = { "Burke", "Connor", "Frank",
"Everett", "Albert", "George",
"Harris", "David" };

IEnumerable<str ingquery = from s in names
where s.Length == 5
orderby s
select s.ToUpper();

foreach (string item in query)
Console.WriteLi ne(item);
}
}

ROTFLMAO! Wow, what progress they're making! Quick guys let's jump on
before we get left behind - we dont want to miss out on this exciting
and mysterious 'foreach' construct or this strange and exotic sounding
'IEnumerable query' thing. To think that python might someday reach such
lofty heights where we'll be able to simply write...

names = ["Burke", "Connor", "Frank", "Everett",
"Albert", "George", "Harris", "David"]

result = [each.upper() for each in names if len(each) == 5]

result.sort()

for each in result: print each


Yes clearly 'the Python crowd' must admit LINQ is 'much better', I'm
sold, in fact off to download my "Free, but limited editions of Visual
Studio 2005 for a single programming language supported by .NET" right away!

OK so maybe I'm being naive here but it looks to me like this new
paradigm's big idea is to use a python + SQL type syntax to access data
in random objects. Big whoop. It's not that difficult to write a
generators that wraps XML files and databases is it?

What am I missing here?


Roger Heathcote.

[sturlamolden]

Re: Linq to Python

On Sep 24, 9:11 pm, bearophileH...@ lycos.com wrote:

In the meantime where I
live lot of people will keep using C# instead of Python and CLisp,
natural selection at work indeed.

Please explain to me what Linq can do that Python does not. Put you
emphasis on why this can't be done with a library, and thus will
require addition of new syntax to the language.

[Duncan Booth]

Re: Linq to Python

r0g <aioe.org@techn icalbloke.comwr ote:

OK so maybe I'm being naive here but it looks to me like this new
paradigm's big idea is to use a python + SQL type syntax to access data
in random objects. Big whoop. It's not that difficult to write a
generators that wraps XML files and databases is it?
>
What am I missing here?

Simple LINQ expressions like the one you gave map easily to Python list
comprehensions. What Microsoft have done though is provide a consistent
implementation which allows you to write complex SQL like expressions which
will work identically on databases or most other sequence types.

Here's another LINQ example:

List<Customercu stomers = GetCustomerList ();

var customerOrderGr oups =
from c in customers
select
new {c.CompanyName,
YearGroups =
from o in c.Orders
group o by o.OrderDate.Yea r into yg
select
new {Year = yg.Key,
MonthGroups =
from o in yg
group o by o.OrderDate.Mon th into mg
select new { Month = mg.Key, Orders = mg }
}
};

ObjectDumper.Wr ite(customerOrd erGroups, 3);

I'm not overly keen on SQL syntax: I think this sort of complex expression
is hard to read. LINQ has a pretty straightforward conversion to method
calls, and for me this consistent set of methods is the important thing
rather than the SQL syntax. e.g. 'group by' maps directly to a call to a
method GroupBy(), so another of Microsoft's LINQ examples is:

public void Linq45() {
string[] anagrams = {"from ", " salt", " earn ", " last ",
" near ", " form "};

var orderGroups = anagrams.GroupB y(
w =w.Trim(),
a =a.ToUpper(),
new AnagramEquality Comparer()
);

ObjectDumper.Wr ite(orderGroups , 1);
}

public class AnagramEquality Comparer : IEqualityCompar er<string>
{
public bool Equals(string x, string y) {
return getCanonicalStr ing(x) == getCanonicalStr ing(y);
}

public int GetHashCode(str ing obj) {
return getCanonicalStr ing(obj).GetHas hCode();
}

private string getCanonicalStr ing(string word) {
char[] wordChars = word.ToCharArra y();
Array.Sort<char >(wordChars);
return new string(wordChar s);
}
}

Python still wins hands down on this example both in verbosity and
readability:

>>anagrams = ["from ", " salt", " earn ", " last ",

" near ", " form "]

>>from itertools import groupby
>>def AnagramKey(w):

return sorted(w.strip( ).upper())

>>for k,words in groupby(sorted( anagrams, key=AnagramKey) ,

key=AnagramKey) :
for w in words:
print w.strip().upper ()
print "..."


EARN
NEAR
....
SALT
LAST
....
FROM
FORM
....

I haven't yet had occasion to use LINQ in anger yet, so I have no idea
whether its an idea to love or to hate. I do think it is good that C# has
effectively sprouted list comprehensions (not to mention anonymous types
and type inferencing) and I expect there may be some aspects worth looking
at for Python but I think they are more likely to lead to itertools
functions than extensions to syntax.

[sturlamolden]

Re: Linq to Python

On Sep 24, 10:59 pm, Duncan Booth <duncan.bo...@i nvalid.invalid>
wrote:

Simple LINQ expressions like the one you gave map easily to Python list
comprehensions. What Microsoft have done though is provide a consistent
implementation which allows you to write complex SQL like expressions which
will work identically on databases or most other sequence types.
han extensions to syntax.

List comprehensions work with any iterable sequence. You can nest them
to make more complex statements. You can also use a generator to
iterate through a database or an XML document. Here is approximately
where linq stops being a marvelous addition to Python.

And I can honestly do without the SQL syntax.

[Thomas G. Willis]

Re: Linq to Python

On Sep 24, 4:59 pm, Duncan Booth <duncan.bo...@i nvalid.invalidw rote:
....

I haven't yet had occasion to use LINQ in anger yet, so I have no idea
whether its an idea to love or to hate. I do think it is good that C# has
effectively sprouted list comprehensions (not to mention anonymous types
and type inferencing) and I expect there may be some aspects worth looking
at for Python but I think they are more likely to lead to itertools
functions than extensions to syntax.

My thoughts exactly when I first looked at it. "Hey C# NOW has list
comprehensions! !! SWEET!!!"

As I understand it LINQ is libraries(Syste m.Data.Linq.dll ,
System.XML.Linq .dll) + syntactic sugar, i wouldn't call that a change
to the language. The addition of lambdas and functions as first class
objects however, that was indeed a language change, and it was a
change for the better that makes LINQ possible, (also makes writing
delegates less cumbersome). To someone other than a C# person, these
features are not new or revolutionary, it's just C# catching up. Kudos
to them for getting there before java.

After some more thought on what might conceivably be missing from
python that LINQ has, that someone might want is the equivalent of
System.XML.Linq .dll, and I can't see any reason why someone couldn't
write it with the exception that there doesn't seem to be a definitive
XML lib for python, meaning generally regarded as the best. That in my
mind would be a prerequisite. But if someone wrote both the XML lib
with the LINQ-ish syntax, maybe it would become the definitive XML
lib.

Again, I personally don't see myself using XML and thus needing that
unless my hand was forced by some business requirement that dictated I
use XML, I would not use it if I had a choice. The SQL LiNQ-ish
though, I think every python ORM has that covered to a degree, and I
use that quite a bit.

[r0g]

Re: Linq to Python

Duncan Booth wrote:

r0g <aioe.org@techn icalbloke.comwr ote:
>

>OK so maybe I'm being naive here but it looks to me like this new
>paradigm's big idea is to use a python + SQL type syntax to access data
>in random objects. Big whoop. It's not that difficult to write a
>generators that wraps XML files and databases is it?
>>
>What am I missing here?

>
Simple LINQ expressions like the one you gave map easily to Python list
comprehensions. What Microsoft have done though is provide a consistent
implementation which allows you to write complex SQL like expressions which
will work identically on databases or most other sequence types.

Hmm, that's a nice idea in theory but I don't think it's the python
killer Mr/Ms bearophile thinks it is. I can't think of any use cases
where this would save me a great deal of time (certainly not enough to
offset the relative slowness of working in C#) but supposing they do
exist this stuff definitely belongs in a module. Seems to me C# is
playing catchup in most ways and this nugget of 'innovation' is just the
exception that proves the rule.

Roger.