If arg(x) is 0 and x is a number, then it is a real number.  Maxima calls 
this carg()  for complex arg.

Carg will also work for some things that are not of numeric type, but 
symbolic in some way.
 Like sqrt(x^2+y^2)   is real  if domain=real

Good luck

On Monday, September 19, 2016 at 7:37:18 AM UTC-7, Jeroen Demeyer wrote:
> Hello, 
> is there a simple way to check in Sage that something is a real number 
> in some form? That is, I am looking for a predicate which returns True 
> on all the following things: 
> int(2) 
> ZZ(2) 
> float(2.3) 
> QQ(23/10) 
> RR(2.3) 
> RDF(2.3) 
> SR(2.3) 
> 2*pi 
> but not on things like 
> "2.3" 
> CC(2.3, 0) 
> SR.symbol("x") 

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