TypeError: can't convert expression to float

[Dario Beraldi]

Hello,

First: Thanks for developing sympy!

I'm getting the error below, using sympy 0.7.5 on python 2.7.8, MacOS 10.6. Could anyone explain what I'm doing wrong?

Many thanks!
Dario

import sympy as s

x= s.Symbol('x')
y= 2*s.sin(x) - 2*s.sin(2*x)
s.solve(y)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 901, in solve
    solution = _solve(f[0], *symbols, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1289, in _solve
    return _solve(newf, symbol, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1289, in _solve
    return _solve(newf, symbol, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1397, in _solve
    result = _tsolve(f_num, symbol, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 2279, in _tsolve
    return _solve(f, sym, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1147, in _solve
    soln = _solve(m, symbol, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1397, in _solve
    result = _tsolve(f_num, symbol, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 2320, in _tsolve
    return _solve(rewrite - rhs, sym, **flags)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1418, in _solve
    for den in dens)]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 1418, in <genexpr>
    for den in dens)]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/solvers/solvers.py", line 285, in checksol
    return abs(val.n(18).n(12, chop=True)) < 1e-9
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/evalf.py", line 1284, in evalf
    result = evalf(self, prec + 4, options)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/evalf.py", line 1184, in evalf
    r = rf(x, prec, options)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/evalf.py", line 457, in evalf_add
    terms = [evalf(arg, prec + 10, options) for arg in v.args]
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/evalf.py", line 1184, in evalf
    r = rf(x, prec, options)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/evalf.py", line 615, in evalf_pow
    re, im, re_acc, im_acc = evalf(base, prec + 5, options)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/evalf.py", line 1190, in evalf
    re, im = x._eval_evalf(prec).as_real_imag()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/polys/rootoftools.py", line 425, in _eval_evalf
    root = findroot(func, x0)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/mpmath/calculus/optimization.py", line 931, in findroot
    fx = f(x0[0])
  File "<string>", line 1, in <lambda>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/sympy/core/expr.py", line 207, in __float__
    raise TypeError("can't convert expression to float")
TypeError: can't convert expression to float

[Aaron Meurer]

This looks like a bug. Can you open an issue for it?

Aaron Meurer

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[Dario Beraldi]

Hi Aaron,
 
I opened on issue on github (https://github.com/sympy/sympy/issues/8155)

Dario