如何在python中撤消“assert”？

Question

在早期的功能中，讓我們稱之為a ，我必須確保a函數不會產生太小的答案（比方說，答案必須大於10）。 但是后來，在第二個函數b （使用函數a作為其輸入之一）中，如果被修改的相同答案小於先前的assert語句，則可以。

有沒有辦法做到這一點？

當函數b產生一個太小的答案時，我試圖保存答案在變量中的小，但是當我運行doctest時我仍然遇到斷言錯誤。

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

斷言不應該用於實現某些代碼的邏輯。 為什么？ 因為你無法保證他們真的被提升了！

$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選項用於“優化”。 但它也刪除了所有斷言}

assert也應該被用於調試 ，檢查在一個良好的書面程序不應該發生的情況。

如果要以某種方式處理特殊輸入，則應使用異常 ：

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

或者您可以編寫一個自定義異常，例如：

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

並將if更改為：

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

然后，當您捕獲異常時，您仍然可以通過異常的grade屬性訪問使其失敗的grade 。

如果您不想在特定情況下引發異常，可以添加一個參數，例如low_grade_is_ok並將該函數修改為：

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

然后在您不想引發異常的函數中，可以使用low_grade_is_ok=True調用它，在這種情況下不會引發異常。