naming objects from string

[manstey]

Hi,

If I have a string, how can I give that string name to a python object,
such as a tuple.

e.g.

a = 'hello'
b=(1234)

and then a function
name(b) = a

which would mean:
hello=(1234)

is this possible?

 

[James Stroud]

Hi,

If I have a string, how can I give that string name to a python object,
such as a tuple.

e.g.

a = 'hello'
b=(1234)

and then a function
name(b) = a

which would mean:
hello=(1234)

is this possible?

Depends on your namespace, but for the local namespace, you can use this:

py> a = object()
py> a
<object object at 0x40077478>
py> locals()['bob'] = a
py> bob
<object object at 0x40077478>

A similar approach can be used for the global namespace.

James

--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/

 

[manstey]

Hi,

But this doesn't work if I do:

a=object()
x='bob'
locals()[x] = a

How can I do this?

Hi,

If I have a string, how can I give that string name to a python object,
such as a tuple.

e.g.

a = 'hello'
b=(1234)

and then a function
name(b) = a

which would mean:
hello=(1234)

is this possible?

Depends on your namespace, but for the local namespace, you can use this:

py> a = object()
py> a
<object object at 0x40077478>
py> locals()['bob'] = a
py> bob
<object object at 0x40077478>

A similar approach can be used for the global namespace.

James

--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095

http://www.jamesstroud.com/

 

[Wildemar Wildenburger]

If I have a string, how can I give that string name to a python object,
such as a tuple.

e.g.

a = 'hello'
b=(1234)

and then a function
name(b) = a

which would mean:
hello=(1234)

is this possible?

Direct answer:
Look up the setattr() functions (DO look it up!). Replace your
name(b) = a line with
setattr(__builtins__, a, b).
There you go.


Hopefully more helpful answer:
One alternative would be using a dictionary. Your example would then
translate to:

a = 'hello'
b = (1234,) # notice the comma!
# without it, it wouldn't be a tuple but a simple
# parenthesized integer
d = {} # your dictionary

d[a] = b # assign the value of b to a key given by a

d[a]

d['hello']

In most cases this will be a LOT less cumbersome compared to messing
with module attributes.

hope that helps a bit
wildemar

 

[Damjan]

Hi,

But this doesn't work if I do:

a=object()
x='bob'
locals()[x] = a

How can I do this?

try
sys.modules[__name__].__dict__[x] = a

But what's the point?

 

[Wildemar Wildenburger]

Hi,

But this doesn't work if I do:

a=object()
x='bob'
locals()[x] = a

How can I do this?

You can. I just copy/pasted your code and it works fine here. (You are
aware that there is whitespace before locals() that you have to remove
before you feed it to the snake?)

What error did you get?

Let me again stress that using locals and globals is a bit contrived,
whereas the dictionary approach from my other post is not.


Just out of curiosity: Why do you want to do this anyway?

wildemar

 

[Wildemar Wildenburger]

try
sys.modules[__name__].__dict__[x] = a

@manstay: You see! Ugly, unreadable trickery!
Hands off this stuff, bad mojo!

You've been told three very different approaches now, which is a pretty
good indicator that there is no obvious way to do it. Which means
another angle to your problem might make it a lot easier.
(btw: Try 'import this' at the python prompt for some wise words.)

Please describe your problem and let us suggest that new angle.

wildemar

 

[manstey]

Hi,

thanks for the suggestions. this is my problem:

I have a metadata file that another user defines, and I don't know
their structure in advance. They might have 300+ structures. the
metadata defines the name and the tuple-like structure when read by
python.

my program reads in the metadata file and then generates python tuples
corresponding to their structures.

so they might provide a list of names, like 'bob','john','pete', with 3
structures per name, such as 'apple','orange','red' and I need 9 tuples
in my code to store their data:

bob_apple=()
bob_orange=()
...
pete_red=()

I then populate the 9 tuples with data they provide in a separate file,
and the filled tuples are then validated against the metadata to make
sure they are isomorphic.

Is this clear?

thanks

 

[manstey]

Hi,

thanks for the suggestions. this is my problem:

I have a metadata file that another user defines, and I don't know
their structure in advance. They might have 300+ structures. the
metadata defines the name and the tuple-like structure when read by
python.

my program reads in the metadata file and then generates python tuples
corresponding to their structures.

so they might provide a list of names, like 'bob','john','pete', with 3
structures per name, such as 'apple','orange','red' and I need 9 tuples
in my code to store their data:

bob_apple=()
bob_orange=()
...
pete_red=()

I then populate the 9 tuples with data they provide in a separate file,
and the filled tuples are then validated against the metadata to make
sure they are isomorphic.

Is this clear?

thanks

 

[Wildemar Wildenburger]

Hi,

thanks for the suggestions. this is my problem:

I have a metadata file that another user defines, and I don't know
their structure in advance. They might have 300+ structures. the
metadata defines the name and the tuple-like structure when read by
python.

my program reads in the metadata file and then generates python tuples
corresponding to their structures.

so they might provide a list of names, like 'bob','john','pete', with 3
structures per name, such as 'apple','orange','red' and I need 9 tuples
in my code to store their data:

bob_apple=()
bob_orange=()
..
pete_red=()

I then populate the 9 tuples with data they provide in a separate file,
and the filled tuples are then validated against the metadata to make
sure they are isomorphic.

Is this clear?

Erm, not exactly but I think I get it.

Note that creating empty tuples will mean that they will always be
empty. They are immutable, basically meaning that you can not change
them after they are created. If you want to create empty data that you
want to fill later on, use lists. Or (which might be more convenient)
put in the data right away).

Generally, since you do not know the names ('bob', 'john', etc.) and the
structures in advance, the best way to store them is in a *variable*.
Here I would suggest dictionaries again. Let me write an example in
pseudo python:

people = {} # data dict
# lets suppose the data from your file is a list of tuples like:
# [('bob',('orange', 'apple', 'red')), ...]
# (I didnt quite get how your data is organized)
for name, structure in list_of_names_from_file:
people[name] = {} # make a new dict for the 'structures'
for item in structure:
people[name][item] = () # empty tuple
# instead of an empty tuple you could fill in your data
# right here, which would save you the extra keyboard mileage

Does that make sense in the context of your application?

wildemar

 

[Ben Finney]

If I have a string, how can I give that string name to a python
object, such as a tuple.

The thing I'd like to know before answering this is: how will you be
using that name to refer to the object later?

 

[Tim Roberts]

If I have a string, how can I give that string name to a python object,
such as a tuple.

e.g.

a = 'hello'
b=(1234)

That's not a tuple. That's an integer. (1234,) is a tuple.

and then a function
name(b) = a

which would mean:
hello=(1234)

is this possible?

Yes, but it's almost never the right way to solve your problem. Use an
explicit dictionary instead.

C:\Tmp>python
Python 2.4.1 (#65, Mar 30 2005, 09:13:57) [MSC v.1310 32 bit (Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.

>>> a='hello'
>>> locals()[a] = 1234
>>> hello 1234
>>>

 

[Gabriel Genellina]

If I have a string, how can I give that string name to a python object,
such as a tuple.

e.g.

a = 'hello'
b=(1234)

and then a function
name(b) = a

which would mean:
hello=(1234)

is this possible?

You may use another object as a namespace:

class X: pass
x = X()

a = 'hello'
b = (1,2,3,4)
setattr(x, a, b)

print x.hello # prints (1,2,3,4)
getattr(x, a) # returns the same

but perhaps if you explain better what you want, we can figure out
how to do that...



Gabriel Genellina
Softlab SRL





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[Fredrik Lundh]

so they might provide a list of names, like 'bob','john','pete', with 3
structures per name, such as 'apple','orange','red' and I need 9 tuples
in my code to store their data:

bob_apple=()
bob_orange=()
..
pete_red=()

I then populate the 9 tuples with data they provide in a separate file,
and the filled tuples are then validated against the metadata to make
sure they are isomorphic.

if you want a dictionary, use a dictionary.

</F>

 

[Jeremy Sanders]

so they might provide a list of names, like 'bob','john','pete', with 3
structures per name, such as 'apple','orange','red' and I need 9 tuples
in my code to store their data:

bob_apple=()
bob_orange=()
..
pete_red=()

I really think you should be using dictionaries here. You don't want to be
messing around creating random variables in the local or global namespace.

For instance

myvals = {}
myvals['bob'] = {}
myvals['pete'] = {}
....
myvals['bob']['apple'] = (1,2,3,4)
myvals['bob']['orange'] = (2,3,4)
myvals['pete']['red'] = (4,5,6,7)

and so on
{'pete': {'red': (4, 5, 6, 7)}, 'bob': {'orange': (2, 3, 4), 'apple': (1, 2,
3,4)}}

 

[Terry Reedy]

Depends on your namespace, but for the local namespace, you can use this:

py> a = object()
py> a
<object object at 0x40077478>
py> locals()['bob'] = a
py> bob
<object object at 0x40077478>

If you put this code within a function, it probably will not work.
locals() is usually a *copy* of the local namespace and writes do not write
back to the namespace itself.

tjr

 

[Roberto Bonvallet]

manstey wrote:
[...]

bob_apple=()
bob_orange=()
..
pete_red=()

I then populate the 9 tuples with data [...]

You cannot "populate" a tuple. If you want to insert the values
individually, you have to use a list. If you insert them all together,
like this: bob_apple = (1, 2, ..., 9), you don't need to initialize
bob_apple with an empty tuple.