在Python的for循环中捕获错误

Question

我有一个在avro数据读取器对象上的for循环。

for i in reader:
    print i

然后在for循环语句中我遇到了Unicode解码错误，所以我想忽略那个特定的记录。于是我做了如下操作：

try:
    for i in reader:
        print i
except:
    pass

但它不会继续执行下去。我该如何解决这个问题？

编辑：添加错误追踪。

    Traceback (most recent call last):
  File "modify.py", line 22, in <module>
    for record in reader:
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/datafile.py", line 362, in next
    datum = self.datum_reader.read(self.datum_decoder) 
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 445, in read
    return self.read_data(self.writers_schema, self.readers_schema, decoder)
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 490, in read_data
    return self.read_record(writers_schema, readers_schema, decoder)
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 690, in read_record
    field_val = self.read_data(field.type, readers_field.type, decoder)
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 468, in read_data
    return decoder.read_utf8()
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 233, in read_utf8
    return unicode(self.read_bytes(), "utf-8")
UnicodeDecodeError: 'utf8' codec can't decode byte 0xb4 in position 14: invalid start byte

可能是因为文件已经损坏了导致的吗？

编辑2：根据答案中的建议，我修改了代码并得到了这个错误。

    Traceback (most recent call last):
  File "modify.py", line 28, in <module>
    print next(iterobject)["filepath"]
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/datafile.py", line 362, in next
    datum = self.datum_reader.read(self.datum_decoder) 
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 445, in read
    return self.read_data(self.writers_schema, self.readers_schema, decoder)
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 490, in read_data
    return self.read_record(writers_schema, readers_schema, decoder)
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 690, in read_record
    field_val = self.read_data(field.type, readers_field.type, decoder)
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 468, in read_data
    return decoder.read_utf8()
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 233, in read_utf8
    return unicode(self.read_bytes(), "utf-8")
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 226, in read_bytes
    return self.read(self.read_long())
  File "/usr/lib/python2.6/site-packages/avro-1.7.7-py2.6.egg/avro/io.py", line 184, in read_long
    b = ord(self.read(1))
TypeError: ord() expected a character, but string of length 0 found

- iLoveCamelCase

---

你能否同时包含异常的回溯信息？并且请修复你代码片段的缩进。 - Tanveer Alam

请问您能否发布一下您在读取器中的数值？ - user4711157

Answer 1

你需要在循环内部使用try/except：

    for i in reader:
       try: 
           print i
       except UnicodeEncodeError:
           pass

顺便说一下，指定要捕获的特定错误类型是一个很好的实践方法（就像我在except UnicodeEncodeError:中所做的那样），否则你可能会使你的代码非常难以调试！

- maxymoo

---

@iLoveCamelCase 如果是这样，那么avro读取器中存在一个bug，除非你想要修改它（修复这个bug），否则在你的脚本中几乎无能为力。 - user707650

我在想如果Avro文件损坏了。 - iLoveCamelCase

Answer 2

如果你的错误出现在for i in中，那么尝试这样做，它会在迭代器中跳过出现UnicodeDecodeError的元素。

iterobject = iter(reader)
while iterobject:
    try:
        print(next(iterobject))
    except StopIteration:
        break
    except UnicodeDecodeError:
        pass

- itzMEonTV

Answer 3

你可以期待特定错误的出现，避免未知错误被忽略。

Python 3.x:

try:
    for i in reader:
        print i
except UnicodeDecodeError as ue:
    print(str(ue))

Python 2.x：

try:
    for i in reader:
        print i
except UnicodeDecodeError, ue:
    print(str(ue))

通过打印错误信息，可以知道发生了什么。当你只使用 except 时，你会接受任何异常（包括晦涩的 RuntimeError），而你永远不会知道发生了什么。有时候这可能是有用的，但它是危险的，通常是一种不好的做法。

- Ericson Willians