Python try/except not working

≯℡__Kan透↙ 提交于 2020-06-27 08:49:08

问题


Trying to get the try/except statement working but having problems. This code will take a txt file and copy the file that is in location row 0 to location of row 1. It works however if i change one of the paths to invalid one it generates an error ftplib.error_perm however the except command is not picking up and everything stops. What am i doing wrong? Python 2.4

import csv
import operator
import sys
import os
import shutil
import logging
import ftplib
import tldftp

def docopy(filename):
        ftp = tldftp.dev()
        inf = csv.reader(open(filename,'r'))
        sortedlist = sorted(inf, key=operator.itemgetter(2), reverse=True)
        for row in sortedlist:
                src = row[0]
                dst = row[1]
                tldftp.textXfer(ftp, "RETR " + src, dst)


def hmm(haha):
    result = docopy(haha);
    try:
        it = iter(result)
    except ftplib.error_perm:
        print "Error Getting File" 


if __name__ == "__main__":
        c = sys.argv[1]
        if (c == ''):
                raise Exception, "missing first parameter - row"
        hmm(c)

回答1:


The except clause will only catch exceptions that are raised inside of their corresponding try block. Try putting the docopy function call inside of the try block as well:

def hmm(haha):
    try:
        result = docopy(haha)
        it = iter(result)
    except ftplib.error_perm:
        print "Error Getting File" 



回答2:


The point in the code which raises the error must be inside the try block. In this case, it's likely that the error is raised inside the docopy function, but that isn't enclosed in a try block.

Note that docopy returns None. As such, you will raise an exception when you try to make an iter out of None -- but it won't be a ftplib.error_perm exception, it'll be a TypeError




回答3:


If you are not sure of what exception will occur, the use the code below, because if especifies for example: except StandardError: and is not that error the exception will not be process.

try:
    # some code
except Exception: # Or only except:
   print "Error" # Python 3: print("Error")



回答4:


I know the OP is ancient, but for folks desperate for answers on this question. I had a similar issue, depending on your IDE, if you have a breakpoint on any of the lines with specific exceptions etc, this can conflict and stop try/except executing.




回答5:


I noticed global exception may not works, e.g. , Ctrl+C when epub.py module perform urllib3 connection trigger KeyboardInterrupt but not able to catch in main thread, the workaround is put my clean up code inside finally, e.g.:

try:
    main()
except Exception as e:
    clean_up_stuff()  #this one never called if keyboard interrupt in module urllib3 thread
finally: #but this work
    clean_up_stuff() 



回答6:


This example is generic for Python3.3+, when decorating a generator function, a decorated generator returns successfully, thus not entering the decorators except, the magic happens with yield from f thus wrapping the yieldable within the decorator:

from types import GeneratorType    

def generic_exception_catcher(some_kwarg: int = 3):
    def catch_errors(func):
        def func_wrapper(*args, **kwargs):
            try:
                f = func(*args, **kwargs)
                if type(f) == GeneratorType:
                    yield from f
                else:
                    return f
            except Exception as e:
                raise e
        return func_wrapper
    return catch_errors

Usage:

@generic_exception_catcher(some_kwarg=4)
def test_gen():
    for x in range(0, 10):
        raise Exception('uhoh')
        yield x

for y in test_gen():
    print('should catch in the decorator')



回答7:


well, I got the same issue in Visual Studio Code , as:

import numpy as np

def func():

    try:

        a = np.log(-9)
        print(a)

    except:
        print ('exception !') # this will never triggered

func()


来源:https://stackoverflow.com/questions/14460189/python-try-except-not-working

易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!