Status: Accepted
Owner: asmeurer
Labels: Type-Defect Priority-Medium WrongResult EasyToFix
New issue 2300 by asmeurer: x.diff(4) doesn't fail
http://code.google.com/p/sympy/issues/detail?id=2300
In [261]: x.diff(4)
Out[261]: x
In [262]: x.diff(2*x
.....: )
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/Users/aaronmeurer/Documents/Python/sympy/sympy/<ipython console> in
<module>()
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/core/expr.py in
diff(self, *symbols, **assumptions)
1474 new_symbols = map(sympify, symbols) # e.g. x, 2, y, z
1475 assumptions.setdefault("evaluate", True)
-> 1476 return Derivative(self, *new_symbols, **assumptions)
1477
1478 def fdiff(self, *indices):
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/core/function.py in
__new__(cls, expr, *symbols, **assumptions)
555
556 if i == iwas: # didn't get an update because of bad
input
--> 557 raise ValueError('Derivative expects Symbol [,
Integer] args but got %s, %s' % (s, count))
558
559 symbol_count.append((s, count))
ValueError: Derivative expects Symbol [, Integer] args but got 2*x, 1
As the error message in the second one suggests, the first argument to diff
should be a Symbol, so x.diff(4) should raise the same ValueError.
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