TypeError求助：float()参数应为字符串/实数而非Value对象

执行draw_dot(d)时触发如下错误：

TypeError: float() argument must be a string or a real number, not 'Value'

错误根源 #

代码里有三处关键问题导致了这个错误：

• __mul__方法参数顺序错误：创建乘法结果的Value对象时，把运算符'*'误传给了_children参数，导致节点的_prev属性变成字符串而非子节点集合，后续遍历逻辑完全混乱。
• trace函数子节点错误包装：v._prev本身就是Value对象的集合，不需要用map(Value, v._prev)重新包装，这会把原Value对象当作新Value的data值，最终导致n.data变成Value类型而非数值。
• draw_dot函数缩进错误：return dot写在了边遍历循环的内部，导致函数提前返回，图形未构建完成。

修复后的完整代码 #

class Value:
    def __init__(self, data, _children=(), _op='', label=''):
        self.data = data
        self._prev = set(_children)
        self._op = _op
        self.label = label
    # REPR allows for nicer looking expression in python
    def __repr__(self):
        return f"Value(data={self.data})"
    def __add__(self, other):
        out = Value(self.data + other.data, (self, other), '+')
        return out
    def __mul__(self, other):
        # 修复：正确传递_children和_op参数
        out = Value(self.data * other.data, (self, other), '*')
        return out

a = Value(2.0, label='a')
b = Value(-3.0, label='b')
c = Value(10.0, label='c')
e = a * b; e.label='e'
# a * b + c
d = e + c; d.label='d'
f = Value(-2.0, label='f')
L = d * f

!pip install graphviz
import graphviz
from graphviz import Digraph

def trace(root):
    # builds a set of all nodes and edges in a graph
    nodes, edges = set(), set()
    def build(v):
        if v not in nodes:
            nodes.add(v)
        # 修复：直接遍历v._prev里的子节点，不需要重新包装成Value
        for child in v._prev:
            edges.add((child, v))
            build(child)
    build(root)
    return nodes, edges

def draw_dot(root):
    dot = Digraph(format='svg', graph_attr={'rankdir': 'LR'})
    nodes, edges = trace(root)
    for n in nodes:
        uid = str(id(n))
        # for any value in the graph create a record (rectanglualr node for it)
        dot.node(name=uid, label="{data %.4f}" % float(n.data), shape='record')
        if n._op:
            # If this value is a result of some operation, create a node for it
            dot.node(name=uid + n._op, label=n._op)
            # and connect this node to it
            dot.edge(uid + n._op, uid)

    for n1, n2 in edges:
        # connect n1 to the op node of n2
        dot.edge(str(id(n1)), str(id(n2)) + n2._op)
    
    # 修复：把return移到循环外面，确保图形构建完成后再返回
    return dot

draw_dot(d)

内容的提问来源于stack exchange，提问作者Leviathan