sympy/sympy — pull request #851 by asmeurer (2011-12-16 23:59:19+00:00)
Title: Give a better warning in Basic.__call__

Now, instead of getting

```pytb
>>> (x + y)(x - y)
Traceback (most recent call last):
File "", line 1, in
TypeError: 'Add' object is not callable
```

You will see

```pytb
>>> (x + y)(x - y)
Traceback (most recent call last):
File "", line 1, in
File "/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/core/basic.py", line 394, in __call__
raise TypeError("'%s' object is not callable. Perhaps you forgot a '*'?" % self.__class__.__name__)
TypeError: 'Add' object is not callable. Perhaps you forgot a '*'?
```