Printing variable names

mylist = [a, b, c]

I want to print out the names of the variables in mylist (not the
values of a, b, and c). How do I go about doing this. Thanks.

Mike

Mike

Mike wrote:

>mylist = [a, b, c]
>
>I want to print out the names of the variables in mylist (not the
>values of a, b, and c). How do I go about doing this. Thanks.
>
>Mike
>
>
There's no simple answer to this. Consider the fact that you can have
more than one name bound to any given mutable instance. What if:

a = range(10)
b = a

mylist = [a]

what name do you want printed for the first item in mylist--'a' or 'b'?

One idea is to use a dictionary instead. Then:

for key, value in mydict.iteritems():
print '%(key)s = %(value)s' % locals()

I'm curious what problem you're trying to solve.

Cheers,

// m

Mark McEahern

On Sun, 18 Jan 2004 11:22:08 -0800, Mike wrote:

> mylist = [a, b, c]
>
> I want to print out the names of the variables in mylist (not the
> values of a, b, and c). How do I go about doing this. Thanks.

The following example shows that this does not really make sense:

a = 1; b = 2; c = 3;
mylist = [a, b, c]
a = 4; b = 5; c = 6;
print mylist
print a, b, c

Result:
[1, 2, 3]
4 5 6

and *not*:
[4, 5, 6]
4 5 6

You might want to google for 'Python object reference' etc.
Moreover, having a look (e.g. in the tutorial) at how Python
passes arguments to functions (mutable and immutable objects)
might help to get a better understanding of what is going on
behind the scenes.

HTH / Nuff

Nuff Said

Mark McEahern <> wrote in message news:<mailman.479.1074455535.12720.python->...
> Mike wrote:
>
> >mylist = [a, b, c]
> >
> >I want to print out the names of the variables in mylist (not the
> >values of a, b, and c). How do I go about doing this. Thanks.
>
> There's no simple answer to this. Consider the fact that you can have
> more than one name bound to any given mutable instance.

Why did you specify "mutable"? The same applies to immutable
instances.

> I'm curious what problem you're trying to solve.

So am I. The question shows up here all the time, but I've never seen
a reason for it.

Dan Bishop

Mark McEahern wrote:
> Mike wrote:
>> mylist = [a, b, c]
>>
>> I want to print out the names of the variables in mylist (not the
>> values of a, b, and c). How do I go about doing this. Thanks.
>> Mike
> ... One idea is to use a dictionary instead. Then:
> for key, value in mydict.iteritems():
> print '%(key)s = %(value)s' % locals()
> I'm curious what problem you're trying to solve.

Mark's questions are very much on target. If the purpose is debugging,
you might be satisfied with something like:

def vnames(value, *dicts):
"""From a value and some dictionaries and give names for the
value"""
result = []
for d in dicts:
result.extend([key for key, val in d.iteritems()
if val is value])
result.append(repr(value))
return result

Which you might use like:

a,b,c = 1,2,3
d,e,f = 5,4,3

for v in range(10):
print v, vnames(v, locals(), globals())

Note: You probably need only locals or globals if you are at the top
level of an interpreter such as Idle or the python shell.
You might prefer '==' to 'is', but remember that 0.0 == 0 == 0L.

-Scott David Daniels

Scott David Daniels

Thanks for the info. That does clear up a few things for me.

This is what I'm trying to accomplish:

Basically I have a list of pointers to functions (or whaterver it's called in
Python). Something like this:

commands = [func1, func2, ...funcN]

This is in a script that I use to test an embedded system through the comport.
I call the script with the command number (func1 etc...), which calls the
corresponding function, which sends a command to the embedded system.

I'd like to be able to call the script with --help and have it spit out
the list of commands (the names func1, func2 etc...).


Mike




Mark McEahern <> wrote in message news:<mailman.479.1074455535.12720.python->...
> Mike wrote:
>
> >mylist = [a, b, c]
> >
> >I want to print out the names of the variables in mylist (not the
> >values of a, b, and c). How do I go about doing this. Thanks.
> >
> >Mike
> >
> >
> There's no simple answer to this. Consider the fact that you can have
> more than one name bound to any given mutable instance. What if:
>
> a = range(10)
> b = a
>
> mylist = [a]
>
> what name do you want printed for the first item in mylist--'a' or 'b'?
>
> One idea is to use a dictionary instead. Then:
>
> for key, value in mydict.iteritems():
> print '%(key)s = %(value)s' % locals()
>
> I'm curious what problem you're trying to solve.
>
> Cheers,
>
> // m

Mike

[Me]
> There's no simple answer to this. Consider the fact that you can have
> more than one name bound to any given mutable instance.

[Dan Bishop]
> Why did you specify "mutable"? The same applies to immutable
> instances.

I didn't think through the immutable issue, that's all. So, in short,
no good reason. <wink>

Cheers,

// m

Mark McEahern

Mike wrote:

> This is what I'm trying to accomplish:
>
> Basically I have a list of pointers to functions (or whaterver it's called
> in
> Python). Something like this:
>
> commands = [func1, func2, ...funcN]
>
> This is in a script that I use to test an embedded system through the
> comport. I call the script with the command number (func1 etc...), which
> calls the corresponding function, which sends a command to the embedded
> system.
>
> I'd like to be able to call the script with --help and have it spit out
> the list of commands (the names func1, func2 etc...).

You're lucky, functions "know" their name:

>>> def func1(): pass
....
>>> def func2(): pass
....
>>> for f in [func1, func2]:
.... print f.__name__
....
func1
func2

Peter

Peter Otten

That makes life easy. Problem solved! Thanks all for the help.

Mike



>
> You're lucky, functions "know" their name:
>
> >>> def func1(): pass
> ...
> >>> def func2(): pass
> ...
> >>> for f in [func1, func2]:
> ... print f.__name__
> ...
> func1
> func2
>
> Peter

Mike