New subject: addition of "nameof" operator

1 Feb 2020


      ...
So this is not likely to ever work in IronPython or Jython.
There are no stability guarantees about the byte-code generated by
CPython, so you may be chasing a moving target here.
You ought to test your code before posting, because I've tried it in
3.5, 3.7 and 3.8 and I get the same error each time:
TypeError: Expected maxsize to be an integer or None


which is a simple error in the call to the lru_cache decorator. After
fixing that, I tried it again in 3.7 and I get this:
>>> x = 1
>>> nameof.nameof(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/srv-steve/python/nameof.py", line 7, in nameof
    return _nameof(frame.f_code, frame.f_lasti)
  File "/home/srv-steve/python/nameof.py", line 17, in _nameof
    assert current_instruction.opname == "CALL_FUNCTION"
AssertionError


--
Steven
I wasn't expecting the Spanish Inquisition! This is not meant for serious
use, just to help people interested in trying out the proposed
functionality. But if you want to be serious, here you go:
https://github.com/alexmojaki/nameof
This is properly tested with CPython 3.4+ and PyPy3. It's basically the
same as the original version, I just tweaked the assertion to allow
'method' calls like nameof.nameof that you did which I wasn't expecting.
The bytecode hasn't changed so drastically across Python versions that this
is unstable.
Python 3.8 allows @lru_cache without arguments, I don't know why that
didn't work for you.
On Sat, Feb 1, 2020 at 4:32 AM python-ideas-request@python.org wrote:
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Proposal for an additional type system (guenter-hofer@aon.at)
Re: Proposal for an additional type system (Chris Angelico)
Re: addition of "nameof" operator (Greg Ewing)
Re: addition of "nameof" operator (Alex Hall)
Re: addition of "nameof" operator (Steven D'Aprano)
Re: addition of "nameof" operator (Christopher Barker)

---------- Forwarded message ----------
From: guenter-hofer@aon.at
To: python-ideas@python.org
Cc:
Bcc:
Date: Fri, 31 Jan 2020 23:45:47 +0100 (CET)
Subject: [Python-ideas] Proposal for an additional type system
The types in most programming languages are only technical types. If a
variable has a type, you may know that it is of type integer or double, but
you don't know if it's a length or an area.
The types required are semantic types.
stypes:
length
area
time
speed
scalar
allowed expressions:
length = length
length + length : length
time = time
time + time : time
scalar * length : length
scalar * time : time
sqrt(area) : length
speed = speed
length / time : speed
foo : time
bar : length
baz : length
bar = 23
baz = 42.3
foo = 17.4
speed'variable = (bar + baz) / foo
baz = length'5
bar = length'foo
Python's dynamic type checking remains.
These type names are all user defined. A type name with a tick before an
expression means that this expression has the semantic type of the type
name. The function names in the allowed expressions statement don't need to
be names of existing functions.
---------- Forwarded message ----------
From: Chris Angelico rosuav@gmail.com
To: python-ideas python-ideas@python.org
Cc:
Bcc:
Date: Sat, 1 Feb 2020 10:22:13 +1100
Subject: [Python-ideas] Re: Proposal for an additional type system
On Sat, Feb 1, 2020 at 10:06 AM guenter-hofer@aon.at wrote:
...
The types in most programming languages are only technical types. If a
variable has a type, you may know that it is of type integer or double, but
you don't know if it's a length or an area.
...
The types required are semantic types.
stypes:
length
area
time
speed
scalar
allowed expressions:
length = length
length + length : length
time = time
time + time : time
scalar * length : length
scalar * time : time
sqrt(area) : length
speed = speed
length / time : speed
This doesn't need a dedicated type system. Those are actual types,
representing units - though you've omitted the actual units. Create a
system of classes with actual units, for instance:
class Meter(int):
    ...
class Second(int):
    ...
Define the operations that are valid on each of these, and what they
return. Define the valid comparisons (for instance, 3 meters is not
less than 4 seconds, and that doesn't make sense).
Python's normal type system is quite powerful, and can handle this
smoothly.
(Once you've had a shot at building this yourself, poke around on PyPI
and see what already exists.)
ChrisA
---------- Forwarded message ----------
From: Greg Ewing greg.ewing@canterbury.ac.nz
To: python-ideas@python.org
Cc:
Bcc:
Date: Sat, 01 Feb 2020 12:33:28 +1300
Subject: [Python-ideas] Re: addition of "nameof" operator
On 1/02/20 6:15 am, Richard Damon wrote:
...
One issue I am seeing is that x = nameof(foo.bar) is crossing the
line between compile time and run time behaviors. The resultant
string, “bar” needs to be generated at compile time, but the
operation still needs to do a check at run-time to determine if that
IS the right result,
I don't think I would bother with the runtime check. This is
mostly going to be used in a context where you're writing out
the same thing again to get its value, e.g.
print("The value of", nameof(foo.bar), "is", foo.bar)


This can be translated to
print("The value of", "bar", "is", foo.bar)


and you'll still get an AttributeError if foo doesn't have
a bar attribute.
--
Greg
---------- Forwarded message ----------
From: Alex Hall alex.mojaki@gmail.com
To: python-ideas@python.org
Cc:
Bcc:
Date: Sat, 1 Feb 2020 01:52:38 +0200
Subject: [Python-ideas] Re: addition of "nameof" operator
Here's a simple runtime implementation that doesn't require any
dependencies or source code access:
import dis
import inspect
from functools import lru_cache
def nameof(_):
    frame = inspect.currentframe().f_back
    return _nameof(frame.f_code, frame.f_lasti)
@lru_cache
def _nameof(code, offset):
    instructions = list(dis.get_instructions(code))
    (current_instruction_index, current_instruction), = (
        (index, instruction)
        for index, instruction in enumerate(instructions)
        if instruction.offset == offset
    )
    assert current_instruction.opname == "CALL_FUNCTION"
    name_instruction = instructions[current_instruction_index - 1]
    assert name_instruction.opname.startswith("LOAD_")
    return name_instruction.argrepr
def test():
    print(nameof(dis))
    print(nameof(dis.get_instructions))
    x = 1
    print(nameof(x))
if __name__ == '__main__':
    test()
---------- Forwarded message ----------
From: "Steven D'Aprano" steve@pearwood.info
To: python-ideas@python.org
Cc:
Bcc:
Date: Sat, 1 Feb 2020 11:52:21 +1100
Subject: [Python-ideas] Re: addition of "nameof" operator
On Sat, Feb 01, 2020 at 01:52:38AM +0200, Alex Hall wrote:
...
Here's a simple runtime implementation that doesn't require any
dependencies or source code access:
import dis
So this is not likely to ever work in IronPython or Jython.
There are no stability guarantees about the byte-code generated by
CPython, so you may be chasing a moving target here.
You ought to test your code before posting, because I've tried it in
3.5, 3.7 and 3.8 and I get the same error each time:
TypeError: Expected maxsize to be an integer or None


which is a simple error in the call to the lru_cache decorator. After
fixing that, I tried it again in 3.7 and I get this:
>>> x = 1
>>> nameof.nameof(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/srv-steve/python/nameof.py", line 7, in nameof
    return _nameof(frame.f_code, frame.f_lasti)
  File "/home/srv-steve/python/nameof.py", line 17, in _nameof
    assert current_instruction.opname == "CALL_FUNCTION"
AssertionError


--
Steven
---------- Forwarded message ----------
From: Christopher Barker pythonchb@gmail.com
To: "Steven D'Aprano" steve@pearwood.info
Cc: python-ideas@python.org
Bcc:
Date: Fri, 31 Jan 2020 18:28:09 -0800
Subject: [Python-ideas] Re: addition of "nameof" operator
I am really confused by this whole thread:
(I know this has all been said in this thread, but I’m summarizing to get
us on the same page for the following comments)
Python has names, and it has values (objects, whatever) when we write
Python, we bind names to values with the = operator. (And other namespace
trickery). Some types of objects do have a __name__ attribute: classes,
functions created with def.
But that name is only sometimes the same as the name(s) it might be bound
to in any given namespace. So what the heck is nameof() supposed to mean? A
few examples:
...
...
...
x = 5
nameof(x)
OK, I suppose that’s “x” — but what is the point of that? You have to know
the name already.
What about:
y = 5
x = 5
(Or x = y)
What is nameof(x) And nameof(y)?
What about nameof(5)?
Now:
def fun():
    pass
I suppose nameof(fun) is “fun”, but again, is that useful?
And now:
Fred = fun
What’s nameof(Fred)
If it’s “Fred” then again, useless.
If it’s “fun” then what about x and y before?
And:
def fun():
    y = something
    return y
lst.append(fun())
nameof(lst[-1])
????
In short, if it means “what is the name of this name” that seems
completely useless?
If it means: what name is this object bound to in this namespace? Than I
can see how one might think that would be useful, but the answer could be:
No name at all
More than one name
A name different than the object’s __name__
And then there is the question of the local vs global namespace, the list
goes on.
This thread has been going on a while:
What am I missing?
-CHB
...
--
Christopher Barker, PhD
Python Language Consulting

Teaching
Scientific Software Development
Desktop GUI and Web Development
wxPython, numpy, scipy, Cython


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Re: addition of "nameof" operator

Alex Hall

Guido van Rossum

Greg Ewing

Guido van Rossum

Johan Vergeer

Guido van Rossum

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