Introspection at the module level?

[Roy Smith]

I've got a module that defines a bunch of constants:

OP_FOO = 1
OP_BAR = 2
OP_BAZ = 37

and so on. The values are all unique. I want to build, at module
import time, a reverse map of these constants, i.e. I want to end up
with:

{1: "OP_FOO", 2: "OP_BAR", 37: "OP_BAZ"}

I can find the appropriate symbols:

for name in dir():
if name.startswith ("OP_"):
print name

But I don't see how to get the values. Getattr() is sort of what I
want, but it works on objects, not modules. Not to mention that I don't
see how to get a handle to the module from inside the module, i.e.
there's no "self".

What am I missing?

 

[Sean Ross]

I've got a module that defines a bunch of constants:

OP_FOO = 1
OP_BAR = 2
OP_BAZ = 37

and so on. The values are all unique. I want to build, at module
import time, a reverse map of these constants, i.e. I want to end up
with:

{1: "OP_FOO", 2: "OP_BAR", 37: "OP_BAZ"}

I'm not sure how to do this "at module import time", but if you just
want to build a reverse dictionary of globals variables that start with
"OP_", you can try this:

rd = dict([(v,k) for k,v in globals().copy().iteritems() if
k.startswith("OP_")])

Not to mention that I don't
see how to get a handle to the module from inside the module, i.e.
there's no "self".

http://groups.google.ca/[email protected]&rnum=6

 

[Peter Hansen]

I've got a module that defines a bunch of constants:

OP_FOO = 1
OP_BAR = 2
OP_BAZ = 37

and so on. The values are all unique. I want to build, at module
import time, a reverse map of these constants, i.e. I want to end up
with:

{1: "OP_FOO", 2: "OP_BAR", 37: "OP_BAZ"}

I can find the appropriate symbols:

for name in dir():
if name.startswith ("OP_"):
print name

But I don't see how to get the values. Getattr() is sort of what I
want, but it works on objects, not modules. Not to mention that I don't
see how to get a handle to the module from inside the module, i.e.
there's no "self".

What am I missing?

globals()

That returns a dict which has those constants in it, so you can ask for
..keys() or .values(), etc.

Think of dir() as just globals().keys() in this case...

-Peter

 

[Terry Reedy]

But I don't see how to get the values. Getattr() is sort of what I
want, but it works on objects, not modules.

Yes it does

m = __import__(__name__)
setattr(m, 'a', 3)
dir(m) ['__builtins__', '__doc__', '__name__', 'a', 'm']
getattr(m, 'a')

3

I don't see how to get a handle to the module from inside the module, i.e.
there's no "self".

You have to define it yourself. See above.

What am I missing?

d={} # then, inside your loop:
d[getattr(m,name)] = name #should do what you said you want

Terry J. Reedy

 

[Sean Ross]

Not to mention that I don't
see how to get a handle to the module from inside the module, i.e.
there's no "self".

There are a couple of ways to get hold of the module from inside. My
previous post contained a link to one method. Here's a couple of other
quick ways:

import __main__ as main

or
{'a': 'A', '__builtins__': <module '__builtin__' (built-in)>, ... }

 

[Skip Montanaro]

Roy> I've got a module that defines a bunch of constants:
Roy> OP_FOO = 1
Roy> OP_BAR = 2
Roy> OP_BAZ = 37

Roy> and so on. The values are all unique. I want to build, at module
Roy> import time, a reverse map of these constants, i.e. I want to end
Roy> up with:

Roy> {1: "OP_FOO", 2: "OP_BAR", 37: "OP_BAZ"}

Have a look at

http://manatee.mojam.com/~skip/python/ConstantMap.py

Skip

 

[Roy Smith]

Have a look at

http://manatee.mojam.com/~skip/python/ConstantMap.py

This pointed me to the simpliest solution. I ended up with:

map = {}
for name, value in globals().items():
if name.startswith ("OP_"):
map[value] = name

which seems to work just fine. Thanks to everybody who responded with
suggestions.

The danger here is that I'm depending on the fact that there are no
globals defined elsewhere in the system which start with "OP_", but that
seems like a pretty minimal risk. In fact, it looks like all the
externally defined globals are of the form __xxx__.