expr.py 文件源码

def as_coefficients_dict(self):
        """Return a dictionary mapping terms to their Rational coefficient.
        Since the dictionary is a defaultdict, inquiries about terms which
        were not present will return a coefficient of 0. If an expression is
        not an Add it is considered to have a single term.

        Examples
        ========

        >>> from sympy.abc import a, x
        >>> (3*x + a*x + 4).as_coefficients_dict()
        {1: 4, x: 3, a*x: 1}
        >>> _[a]
        0
        >>> (3*a*x).as_coefficients_dict()
        {a*x: 3}

        """
        c, m = self.as_coeff_Mul()
        if not c.is_Rational:
            c = S.One
            m = self
        d = defaultdict(int)
        d.update({m: c})
        return d