sympy/sympy — pull request #2356 by skirpichev (2013-08-05 21:51:14+00:00)
Title: Don't evaluate derivatives for O expressions

Quote from [issue 1756](http://code.google.com/p/sympy/issues/detail?id=1756#c1):
> Strictly speaking, even a O(1) function could have a derivative that is as large as you like, so long as the function itself is bounded by a constant. Consider for example sin(x**2).

Lets keep derivatives unevaluated:
```
In [1]: O(1, x).diff(x)
Out[1]:
d
──(O(1))
dx
```