Hi,
On 29/08/12 12:51, Chris Smith wrote:
> On Wed, Aug 29, 2012 at 2:27 PM, Juha Jeronen <[email protected]> wrote:
>> Hi all,
>>
>> This time a question: is there a preferred way of getting a complete
>> list of symbols reserved by SymPy, i.e. atoms which have a default
>> meaning (E, pi, EulerGamma, oo, etc.)?
> These are the singletoms (below, ignore methods with `__`). But they
> can all be overwritten. The only reserved symbols that don't become
> symbols upon sympification are Q-COSINE (the C will actually parse
> like a symbol so in that sense it's not reserved; the "-" could help
> you remember that).
Thanks for the quick reply.
Ok.
>>>> dir(S)
> ['Catalan', 'ComplexInfinity', 'EmptySet', 'EulerGamma', 'Exp1',
> 'GoldenRatio', 'Half', 'IdentityFunction', 'ImaginaryUnit',
> 'Infinity', 'Integers', 'NaN', 'Naturals', 'NegativeInfinity',
> 'NegativeOne', 'NumberSymbol', 'One', 'Pi', 'Reals', 'UniversalSet',
> 'Zero', '__call__', '__class__', '__delattr__', '__doc__',
> '__format__', '__getattribute__', '__hash__', '__init__',
> '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__',
> '__setattr__', '__sizeof__', '__slots__', '__str__',
> '__subclasshook__']
Thanks!
So, dir(S) is the preferred way of getting a complete list :)
It also works in both old and new versions, so that's good. I think the
only remaining question is if this is likely to stay working for the
foreseeable future?
(The point being, at least my mind would be more at ease if there was a
dedicated API method.)
Proceeding from this point, it seems that in order to get the
corresponding strings that sympify() converts into these objects, the
additional map(...) step is needed. What I mean is:
import re
import sympy as sy
L = dir(sy.S)
objnames = filter( lambda name: re.match("__", name) is None, L )
strs = map( lambda name: str(eval("sy.S.%s" % name)), objnames )
print objnames
print strs
For example, running this on 0.6.7 (sorry for the old version; running
on Debian Stable at the moment) we get
objnames = ['Catalan', 'ComplexInfinity', 'EulerGamma', 'Exp1',
'GoldenRatio', 'ImaginaryUnit', 'Infinity', 'NaN', 'NegativeInfinity',
'NegativeOne', 'One', 'Pi', 'Zero']
strs = ['Catalan', 'zoo', 'EulerGamma', 'E', 'GoldenRatio', 'I', 'oo',
'nan', '-oo', '-1', '1', 'pi', '0']
with "strs" being what I was after. (In real-world use, I would further
filter out anything that matches is_Number, in order to drop the obvious
0, -1, 1.)
This further conversion is important because:
import sympy as sy
pi = sy.sympify("pi")
print type(pi) # => sympy.core.numbers.Pi
# but:
pi = sy.sympify("Pi")
print type(pi) # => sympy.core.symbol.Symbol (<--- !!!)
...so the "reserved symbol" (in the sense I intended) should be
lowercase "pi".
>> And finally, a related question: is there a way to get a human-readable
>> description for a reserved name (e.g. "zoo" -> "complex infinity")? I
>> didn't find anything in the API for this.
> Not sure how to go further than
>
>>>> type(oo)
> <class 'sympy.core.numbers.Infinity'>
Aaaahh, the type! Nice.
Thanks!
The final code that I ended up using (modulo variable naming and
comments) is:
---8<---8<---8<---
rawnames = filter( lambda name: re.match("__", name) is None, dir(sy.S) )
objs = map( lambda name: eval("sy.S.%s" % name), rawnames )
objs = filter( lambda obj: not obj.is_Number, objs )
strs = map( lambda obj: str(obj), objs )
descs = {}
for obj,name in zip(objs,strs):
descs[name] = str(type(obj))
# now:
# - strs[] contains all reserved atoms, except literal numbers
# - descs{} contains a human-readable description of each item.
---8<---8<---8<---
I would like to suggest adding an API method for this (e.g. with the
is_Number check made optional), unless my use case is too specific for
general use :)
-J
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