operatorordering.py 文件源码

def _normal_order_terms(expr, recursive_limit=10, _recursive_depth=0):
    """
    Helper function for normal_order: look through each term in an addition
    expression and call _normal_order_factor to perform the normal ordering
    on the factors.
    """

    new_terms = []
    for term in expr.args:
        if isinstance(term, Mul):
            new_term = _normal_order_factor(term,
                                            recursive_limit=recursive_limit,
                                            _recursive_depth=_recursive_depth)
            new_terms.append(new_term)
        else:
            new_terms.append(term)

    return Add(*new_terms)