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from sympy/core/function.py

def diff(f, *symbols, **kwargs):    """    Differentiate f with respect to symbols.    This is just a wrapper to unify .diff() and the Derivative class; its    interface is similar to that of integrate().  You can use the same    shortcuts for multiple variables as with Derivative.  For example,    diff(f(x), x, x, x) and diff(f(x), x, 3) both return the third derivative    of f(x).    You can pass evaluate=False to get an unevaluated Derivative class.  Note    that if there are 0 symbols (such as diff(f(x), x, 0), then the result will    be the function (the zeroth derivative), even if evaluate=False.将f用符号区分。     这只是统一.diff（）和Derivative类的包装器； 它的接口类似于Integrated（）的接口。 您可以对多个变量使用与“衍生”相同的快捷方式。 例如，diff（f（x），x，x，x）和diff（f（x），x，3）都返回f（x）的三阶导数。     您可以传递validate = False来获得未评估的派生类。 请注意，如果有0个符号（例如diff（f（x），x，0）），那么即使评估= False，结果也将是该函数（零导数）。         Examples    ========    >>> from sympy import sin, cos, Function, diff    >>> from sympy.abc import x, y    >>> f = Function('f')    >>> diff(sin(x), x)    cos(x)    >>> diff(f(x), x, x, x)    Derivative(f(x), (x, 3))    >>> diff(f(x), x, 3)    Derivative(f(x), (x, 3))    >>> diff(sin(x)*cos(y), x, 2, y, 2)    sin(x)*cos(y)    >>> type(diff(sin(x), x))    cos    >>> type(diff(sin(x), x, evaluate=False))    
   
        >>> type(diff(sin(x), x, 0))    sin    >>> type(diff(sin(x), x, 0, evaluate=False))    sin    >>> diff(sin(x))    cos(x)    >>> diff(sin(x*y))    Traceback (most recent call last):    ...    ValueError: specify differentiation variables to differentiate sin(x*y)    Note that ``diff(sin(x))`` syntax is meant only for convenience    in interactive sessions and should be avoided in library code.    References    ==========    http://reference.wolfram.com/legacy/v5_2/Built-inFunctions/AlgebraicComputation/Calculus/D.html    See Also    ========    Derivative    idiff: computes the derivative implicitly    """    if hasattr(f, 'diff'):        return f.diff(*symbols, **kwargs)    kwargs.setdefault('evaluate', True)    return Derivative(f, *symbols, **kwargs)