如何在python中撤消“assert”？

Question

在早期的功能中，让我们称之为a ，我必须确保a函数不会产生太小的答案（比方说，答案必须大于10）。 但是后来，在第二个函数b （使用函数a作为其输入之一）中，如果被修改的相同答案小于先前的assert语句，则可以。

有没有办法做到这一点？

当函数b产生一个太小的答案时，我试图保存答案在变量中的小，但是当我运行doctest时我仍然遇到断言错误。

def grade_on_project(student_project_score, max_score, overall_score):
    project_grade = student_project_score / max_project_score
    assert project_grade > 0.6 # (student fails the class if any of their scores on a project are too low)
    overall_score +=student_project_score
    return overall_score

def who_fails_first(operation, person1, person2)
    if (operation(person1, max_score, person1) <= 150 and (operation(person2, max_score, overall_score) > 150:
        print(student 1 failed)
    if (operation(person2, max_score, overall_score) <= 150 and (operation(person1, max_score, overall_score) > 150:
        print(student 2 failed)

 who_fails_first(grade_on_project, 5, 9)

Answer 1

断言不应该用于实现某些代码的逻辑。 为什么？ 因为你无法保证他们真的被提升了！

$python -c 'assert False'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AssertionError
$python -O -c 'assert False'   # doesn't raise an error!
$

^{-O选项用于“优化”。 但它也删除了所有断言}

assert也应该被用于调试 ，检查在一个良好的书面程序不应该发生的情况。

如果要以某种方式处理特殊输入，则应使用异常 ：

def grade_on_project(student_project_score, max_score, overall_score):
    project_grade = student_project_score / max_project_score

    if project_grade > 0.6:
        raise ValueError('Student fails if at least one project grade is too low.')

    overall_score +=student_project_score
    return overall_score

或者您可以编写一个自定义异常，例如：

class StudentFailed(ValueError):
    def __init__(self, message, grade):
        super(StudentFailed, self).__init__(message)
        self.grade = grade

并将if更改为：

if project_grade > 0.6:
    raise StudentFailed('One project has grade too low.', project_grade)

然后，当您捕获异常时，您仍然可以通过异常的grade属性访问使其失败的grade 。

如果您不想在特定情况下引发异常，可以添加一个参数，例如low_grade_is_ok并将该函数修改为：

def grade_on_project(student_project_score, max_score,
                     overall_score, low_grade_is_ok=False):
    project_grade = student_project_score / max_project_score

    if not low_grade_is_ok and project_grade > 0.6:
        raise ValueError('Student fails if at least one project grade is too low.')

    overall_score +=student_project_score
    return overall_score

然后在您不想引发异常的函数中，可以使用low_grade_is_ok=True调用它，在这种情况下不会引发异常。