Try/except 在 Python - 在 range/eof 之外

Question

我是 Python 的初学者。我刚刚在Python中遇到了try/except。当我使用 except 时，如果没有 Eof 问题或超出范围，我很难处理这些事情。

我想遍历元组列表以检查有多少学生通过了考试，有多少学生未通过考试。不幸的是，并非所有学生都有 pass/will 子句。

如何在不出现运行时错误的情况下解决这个问题？

try:
    students = [('Timmy', 95, 'Will pass'), ('Martha', 70), ('Betty', 82, 'Will pass'),
                    ('Stewart', 50, 'Will not pass'), ('Ashley', 68), ('Natalie', 99, 'Will pass'), ('Archie', 71),
                    ('Carl', 45, 'Will not pass')]
    passing = {'Will pass': 0, 'Will not pass': 0}

    for tup in students:
        if tup[2] == "Will pass":
                passing['Will pass'] += 1
        elif tup[2] == "Will not pass":
            passing["Will not pass"] += 1
try:
    students = [('Timmy', 95, 'Will pass'), ('Martha', 70), ('Betty', 82, 'Will pass'),
                    ('Stewart', 50, 'Will not pass'), ('Ashley', 68), ('Natalie', 99, 'Will pass'), ('Archie', 71),
                    ('Carl', 45, 'Will not pass')]
    passing = {'Will pass': 0, 'Will not pass': 0}

    for tup in students:
        if tup[2] == "Will pass":
                passing['Will pass'] += 1
        elif tup[2] == "Will not pass":
            passing["Will not pass"] += 1

except IndexError:
    for tup in students:
        print(tup[2])




    # ...

Answer 1

首先，read the docs - lots of examples in there, see also IndexError.

访问无效索引时如何不崩溃。

students = [('Timmy', 95, 'Will pass'), ('Martha', 70), ('Betty', 82, 'Will pass'),
            ('Stewart', 50, 'Will not pass'), ('Ashley', 68), ('Natalie', 99, 'Will pass'),
            ('Archie', 71), ('Carl', 45, 'Will not pass')]
passing = {'Will pass': 0, 'Will not pass': 0}

for tup in students:
    try:
        if tup[2] == "Will pass":
            passing['Will pass'] += 1
        elif tup[2] == "Will not pass":
            passing["Will not pass"] += 1
    except IndexError:
        # handle error here
        pass

另一个没有 try/except 的解决方案 - 只需检查元组的 len()：

students = [('Timmy', 95, 'Will pass'), ('Martha', 70), ('Betty', 82, 'Will pass'),
            ('Stewart', 50, 'Will not pass'), ('Ashley', 68), ('Natalie', 99, 'Will pass'),
            ('Archie', 71), ('Carl', 45, 'Will not pass')]
counter = [0, 0, 0]

for student in students:
    if len(student) > 2 and student[2] == "Will pass":
        counter[0] += 1
    elif len(student) > 2 and student[2] == "Will not pass":
        counter[1] += 1
    else:
        counter[2] += 1

print("Passing:", counter[0], "Not passing:", counter[1], "Missing attribute:", counter[2])

这是另一个使用 filter、map 和 reduce 的解决方案，只是为了好玩：

from functools import reduce

students = [('Timmy', 95, 'Will pass'), ('Martha', 70), ('Betty', 82, 'Will pass'),
            ('Stewart', 50, 'Will not pass'), ('Ashley', 68), ('Natalie', 99, 'Will pass'),
            ('Archie', 71), ('Carl', 45, 'Will not pass')]

p, n = reduce(
    lambda x, y: (x[0] + y[0], x[1] + y[1]),
    map(
        lambda x: (1,0) if x[2] == 'Will pass' else (0,1),
        filter(
            lambda x: len(x) > 2,
            students
        )
    ),
    (0,0)
)

print("Passing:", p, "Not passing:", n)

Answer 2

我看你想练习try/except。在那种情况下你应该记住：

每个 try 块必须有一个 except 块，否则会抛出错误
您只需要将代码块放在可能发生错误的 try 块中。

因此您可以对代码进行以下修改：

students = [('Timmy', 95, 'Will pass'), ('Martha', 70), ('Betty', 82, 'Will pass'),
                ('Stewart', 50, 'Will not pass'), ('Ashley', 68), ('Natalie', 99, 'Will pass'), ('Archie', 71),
                ('Carl', 45, 'Will not pass')]
passing = {'Will pass': 0, 'Will not pass': 0}

for tup in students:
    try:
        passing[tup[2]] += 1
    except:
        print('No status for student: ', tup[0])
print(passing)

这会产生以下输出：

No status for student:  Martha
No status for student:  Ashley
No status for student:  Archie
{'Will pass': 3, 'Will not pass': 2}

Try/except 在 Python - 在 range/eof 之外

Try/except in Python - out of range/eof

python

try-except