There's a "return" missing:
$ git diff
diff --git a/sympy/functions/elementary/trigonometric.py
b/sympy/functions/elementary/trigonometric.py
index 635e7f2..b7a0ad1 100644
--- a/sympy/functions/elementary/trigonometric.py
+++ b/sympy/functions/elementary/trigonometric.py
@@ -3070,4 +3070,4 @@ def fdiff(self, argindex):
def _eval_evalf(self, prec):
y, x = self.args
if x.is_extended_real and y.is_extended_real:
- super(atan2, self)._eval_evalf(prec)
+ return super(atan2, self)._eval_evalf(prec)
Also it checks if the args are real so it looks like you might need to
declare your variables a and y with real=True. If you do that then the
result is caculated as: 0.785398163397448
Can you open an issue on Github for this?
On Tue, 20 Aug 2019 at 15:34, Ville Bergholm <ville.bergh...@iki.fi> wrote:
>
> I've been trying to use sympy.Symbol to implement a system where the
> numerical value of a symbolic quantity is only fixed when it is evaluated
> using evalf().
> To accomplish this I've redefined _eval_evalf() to return the aforementioned
> value (a fixed 5.0 in the toy example below).
>
> This works fine with basic algebraic operations and most SymPy functions.
> However, for some reason atan2 seems to behave differently and _eval_evalf is
> never called.
> Is this a bug, or have I misunderstood the purpose of _eval_evalf?
>
>
> import sympy
> import sympy.functions as syf
>
> class A(sympy.Symbol):
> def _eval_evalf(self, prec):
> print('*')
> return sympy.Float(5.0)
>
> x = A('X')
> y = A('Y')
> print('polynomial:')
> print((2*x-4+y).evalf()) # works fine
> print('atan:')
> print(syf.atan(y / x).evalf()) # works fine
> print('beta:')
> print(syf.beta(y, x).evalf()) # works fine
> print('atan2:')
> print(syf.atan2(y, x).evalf()) # prints "atan2(Y, X)", does not call
> A._eval_evalf
>
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