机器学习建模报错 TypeError:plot_learning_curve() got an unexpected keyword argument 'ax'

以下是我的代码，该导入的库没有任何问题，代码检查了多遍依然正确

def plot_learning_curve(estimator,title, X, y,
                        x=None, #选择子图
                        ylim=None, #设置纵坐标的取值范围
                        cv=None, #交叉验证
                        n_jobs=None #设定索要使用的线程
                        ):
    
    train_sizes,train_scores,test_scores = learning_curve(estimator,
                                                           X, y,
                                                           shuffle=True
                                                           ,cv=cv
                                                           ,random_state=420
                                                            ,n_jobs=n_jobs)
   
    ax.set_title(title)#设置标题
    if ax == None:
        ax = plt.gca()
    else:
        ax = plt.figure()
    
    if ylim is not None:
        ax.set_ylim(*ylim)
    ax.set_xlabel("Training examples")
    ax.set_ylabel("Score")
    ax.grid() #绘制网格，不是必须
    ax.plot(train_sizes,np.mean(train_scores, axis=1),'o-',color="r",label="Training score")
    ax.plot(train_sizes,np.mean(test_scores, axis=1),'o-',color="g",label="Test score")
    ax.legend(loc="best")
    return ax
cv = KFold(n_splits=5, shuffle = True, random_state=42)#交叉验证模式
plot_learning_curve(XGBR(n_estimators=100,random_state=420),"XGB",Xtrain,Ytrain,
                    ax=None,cv=cv)
plt.show()

报错如下：
TypeError Traceback (most recent call last)
in
----> 1 plot_learning_curve(XGBR(n_estimators=100,random_state=420),"XGB",Xtrain,Ytrain,
2 ax=None,cv=cv)
3 plt.show()

TypeError:

```python

``` plot_learning_curve() got an unexpected keyword argument 'ax'

ax 没有定义？ fig, ax = plt.subplots()
这个创建的吧