TypeError: __str__ returned non-string (type WebStepInfo)

class CaseStep(models.Model):
    id = models.AutoField(primary_key=True)
    casetep = models.ForeignKey(WebStepInfo, on_delete=models.CASCADE, verbose_name="测试步骤")
    casedata = models.chaCharField("测试数据", max_length=200, default=‘null‘)
    stepresult = models.BooleanField("测试结果", default=False)
    webcase = models.ForeignKey(WebCase, on_delete=models.CASCADE, verbose_name="所属用例")
    update_time = models.DateTimeField("最近更改时间", auto_now=True)
    create_time = models.DateTimeField("创建时间", auto_now_add=True)

    class Meta:
        db_table = "CaseInfo"

    def __str__(self):
        return self.casetep

    def __str__(self):
        return self.casetep.stepname