2022年4月24日：面向初学者的Python--Python错误处理（很难理解）

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原创 2022-04-28 18:53:33 1.5k 阅读 AI 写同款· GEO 优化 ›

python写代码过程中的坑230915 要判断节点 i 是否是列表 a 中的最后一个值，可以使用以下方法：i = 5else:在上述代码中，我们将列表 a 初始化为 [1, 2, 3, 4, 5]，并将节点 i 设置为 5。然后我们使用条件语句 if 来检查 i 是否等于列表 a 的最后一个值，通过使用 a[-1] 可以获取列表 a 的最后一个元素。阅读详情

使用回溯查找错误

Python中的异常是语言的核心功能。

回溯

回溯几乎始终包含以下信息：

涉及对每个函数的每次调用的所有文件路径
与每个文件路径关联的行号
产生异常时涉及的函数、方法或类的名称
引发的异常的名称

Python 3.10.2 (tags/v3.10.2:a58ebcc, Jan 17 2022, 14:12:15) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> open("/path/to/mars.jpg")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: '/path/to/mars.jpg'
>>>

处理异常

try和except块

如果文件或目录不存在，则会引发FileNotFoundError。如果想要处理此异常，可以使用try和except块。

Python 3.10.2 (tags/v3.10.2:a58ebcc, Jan 17 2022, 14:12:15) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> try:
...     open('config.txt')
... except FileNotFoundError:
...     print("Couldn't find the config.txt file!")
...
Couldn't find the config.txt file!
>>>

在 try 关键字之后，添加可能引发异常的代码。接下来，添加 except 关键字与可能的异常，后跟在该条件发生时需要运行的任何代码。由于 config.txt 在系统中不存在，因此 Python 将打印配置文件不存在。 try 和 except 块以及有用的消息会阻止回溯，并仍通知用户有关此问题的信息。

删除config.txt文件，创建一个文件config.txt，还是显示不了IsADirectoryError的错误信息。

无文件：

有文件：

IsADirectoryError，暂时没有机会遇到。

如果导航系统负载过大，并且文件系统变得太忙，则很有必要同时捕获 BlockingIOError 和 TimeOutError。

有文件：

无文件：

暂时没有机会遇到BlockingIOError和TimeoutError。

如果需要访问与异常相关的错误，则必须更新 except 行以包含 as 关键字。如果异常太过普通，则这种方法就非常方便并且错误消息会很有用：

Python 3.10.2 (tags/v3.10.2:a58ebcc, Jan 17 2022, 14:12:15) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> try:
...     open("mars.jpg")
... except FileNotFoundError as err:
...     print("got a problem trying to read the file:",err)
...
got a problem trying to read the file: [Errno 2] No such file or directory: 'mars.jpg'
>>>
>>> try:
...     open("mars.jpg")
... except OSError as err:
...     if err.errno==2:
...             print("Couldn't find the config.txt file!")
...     elif err.errno==13:
...             print("Found config.txt but couldn't read it")
...
Couldn't find the config.txt file!
>>>

处理错误时：

错误不指出真正的问题。

错误给出与实际问题不匹配的输出。

错误不指示可以执行哪些操作来解决问题。

引发异常

Python 3.10.2 (tags/v3.10.2:a58ebcc, Jan 17 2022, 14:12:15) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> def water_left(astronauts,water_left,days_left):
...     daily_usage=astronauts*11
...     total_usage=daily_usage*days_left
...     total_water_left=water_left-total_usage
...     return f"Total water left after {days_left} day is: {total_water_left} liters"
...
>>> water_left(5,100,2)
'Total water left after 2 day is: -10 liters'
>>> def water_left(astronauts,water_left,days_left):
...     daily_usage=astronauts*11
...     total_usage=daily_usage*days_left
...     total_water_left=water_left-total_usage
...     if total_water_left<0:
...             raise RuntimeError(f"There is not enough water for {astronauts} astronauts after {day_left} days!")
...     return f"Total water left after {day_left} days is: {total_water_left} liters"
...
>>> water_left(5,100,2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in water_left
NameError: name 'day_left' is not defined. Did you mean: 'days_left'?
>>> try:
...
  File "<stdin>", line 2

    ^
IndentationError: expected an indented block after 'try' statement on line 1
>>> def water_left(astronauts,water_left,days_left):
...     daily_usage=astronauts*11
...     total_usage=daily_usage*days_left
...     total_water_left=water_left-total_usage
...     if total_water_left<0:
...             raise RuntimeError(f"There is not enough water for {astronauts} astronauts after {day_left} days!")
...     return f"Total water left after {days_left} days is: {total_water_left} liters"
...
>>> water_left(5,100,2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in water_left
NameError: name 'day_left' is not defined. Did you mean: 'days_left'?
>>> def water_left(astronauts,water_left,days_left):
...     daily_usage=astronauts*11
...     total_usage=daily_usage*days_left
...     total_water_left=water_left-total_usage
...     if total_water_left<0:
...             raise RuntimeError(f"There is not enough water for {astronauts} astronauts after {days_left} days!")
...     return f"Total water left after {days_left} days is: {total_water_left} liters"
...
>>> water_left(5,100,2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in water_left
RuntimeError: There is not enough water for 5 astronauts after 2 days!
>>> def water_left(astronauts,water_left,days_left):
...     for argument in[astronauts,water_left,day_left]:
...             try:
...                     argument/10
...             except TypeError:
...                     raise TypeError(f"All arguments must be of type int, but received: '{argument}'")
... daily_usage=astronauts*11
  File "<stdin>", line 7
    daily_usage=astronauts*11
    ^^^^^^^^^^^
SyntaxError: invalid syntax
>>> def water_left(astronauts,water_left,days_left):
...     for argument in[astronauts,water_left,day_left]:
...             try:
...                     argument/10
...             except TypeError:
...                     raise TypeError(f"All arguments must be of type int, but received: '{argument}'")
...     daily_usage=astronauts*11
...     total_usage=daily_usage*days_left
...     total_water_left=water_left-total_usage
...     if total_water_left<0:
...             raise RuntimeError(f"There is not enough water for {astronauts} astronauts after {after_left} days!")
...     return f"Total water left after {days_left} days is: {total_water_left} liters"
...
>>> water_left("3","200",None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in water_left
NameError: name 'day_left' is not defined. Did you mean: 'days_left'?
>>> def water_left(astronauts,water_left,days_left):
...     for argument in[astronauts,water_left,days_left]:
...             try:
...                     argument/10
...             except TypeError:
...                     raise TypeError(f"All arguments must be of type int, but received: '{argument}'")
...     daily_usage=astronauts*11
...     total_usage=daily_usage*days_left
...     total_water_left=water_left-total_usage
...     if total_water_left<0:
...             raise RuntimeError(f"There is not enough water for {astronauts} astronauts after {after_left} days!")
...     return f"Total water left after {days_left} days is: {total_water_left} liters"
...
>>> water_left("3","200",None)
Traceback (most recent call last):
  File "<stdin>", line 4, in water_left
TypeError: unsupported operand type(s) for /: 'str' and 'int'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 6, in water_left
TypeError: All arguments must be of type int, but received: '3'
>>>