Python干净的方式来包装单独的语句在try除了块 [英] Python clean way to wrap individual statements in a try except block

问题描述

我目前正在做一些Python的自动化Excel与com。它完全功能，并做我想要的，但我发现了一些令人惊讶的。有时，我使用的一些Excel命令将失败，有一个例外，没有明显的原因。其他时候，他们会工作。

I'm currently doing some Python automation of Excel with com. It's fully functional, and does what I want, but I've discovered something surprising. Sometimes, some of the Excel commands I use will fail with an exception for no apparent reason. Other times, they will work.

在我正在做的VB等效代码中，这个问题显然被认为是正常的，并且贴上了 On Error Resume Next 语句。

In the VB equivalent code for what I'm doing, this problem is apparently considered normal, and is plastered over with a On Error Resume Next statement. Python does not have said statement, of course.

我不能在中包装整个集合，除了循环，因为它可能失败一半，并没有完全正确。那么，什么是一个python的方式来包装几个独立的语句到try除了块？具体来说，比以下更干净的东西：

I can't wrap up the whole set in a try except loop, because it could "fail" halfway through and not complete properly. So, what would be a pythonic way to wrap several independent statements into a try except block? Specifically, something cleaner than:

try:
   statement
except:
   pass
try:
   statement
except:
   pass

相关代码是 excel.Selection.Borders 位。

def addGridlines(self, infile, outfile):
    """convert csv to excel, and add gridlines"""
    # set constants for excel
    xlDiagonalDown = 5
    xlDiagonalUp = 6
    xlNone = -4142
    xlContinuous = 1
    xlThin = 2
    xlAutomatic = -4105
    xlEdgeLeft = 7
    xlEdgeTop = 8
    xlEdgeBottom = 9
    xlEdgeRight = 10
    xlInsideVertical = 11
    xlInsideHorizontal = 12
            # open file
    excel = win32com.client.Dispatch('Excel.Application')
    workbook = excel.Workbooks.Open(infile)
    worksheet = workbook.Worksheets(1)

    # select all cells
    worksheet.Range("A1").CurrentRegion.Select()
    # add gridlines, sometimes some of these fail, so we have to wrap each in a try catch block
    excel.Selection.Borders(xlDiagonalDown).LineStyle = xlNone
    excel.Selection.Borders(xlDiagonalUp).LineStyle = xlNone
    excel.Selection.Borders(xlDiagonalUp).LineStyle = xlNone
    excel.Selection.Borders(xlEdgeLeft).LineStyle = xlContinuous
    excel.Selection.Borders(xlEdgeLeft).Weight = xlThin
    excel.Selection.Borders(xlEdgeLeft).ColorIndex = xlAutomatic
    excel.Selection.Borders(xlEdgeTop).LineStyle = xlContinuous
    excel.Selection.Borders(xlEdgeTop).Weight = xlThin
    excel.Selection.Borders(xlEdgeTop).ColorIndex = xlAutomatic
    excel.Selection.Borders(xlEdgeBottom).LineStyle = xlContinuous
    excel.Selection.Borders(xlEdgeBottom).Weight = xlThin
    excel.Selection.Borders(xlEdgeBottom).ColorIndex = xlAutomatic
    excel.Selection.Borders(xlEdgeRight).LineStyle = xlContinuous
    excel.Selection.Borders(xlEdgeRight).Weight = xlThin
    excel.Selection.Borders(xlEdgeRight).ColorIndex = xlAutomatic
    excel.Selection.Borders(xlInsideVertical).LineStyle = xlContinuous
    excel.Selection.Borders(xlInsideVertical).Weight = xlThin
    excel.Selection.Borders(xlInsideVertical).ColorIndex = xlAutomatic
    excel.Selection.Borders(xlInsideHorizontal).LineStyle = xlContinuous
    excel.Selection.Borders(xlInsideHorizontal).Weight = xlThin
    excel.Selection.Borders(xlInsideHorizontal).ColorIndex = xlAutomatic
    # refit data into columns
    excel.Cells.Select()
    excel.Cells.EntireColumn.AutoFit()
    # save new file in excel format
    workbook.SaveAs(outfile, FileFormat=1)
    workbook.Close(False)
    excel.Quit()
    del excel

更新：

需要对错误位进行一点解释。在我的测试机器上的两个相同的运行，具有相同的代码，在同一文件上，产生相同的结果。一个运行会为每个 xlInsideVertical 行抛出异常。其他每个 xlInsideHorizo​​ntal 引发异常。

Perhaps a bit of explanation on the error bit is required. Two identical runs on my test machine, with identical code, on the same file, produce the same result. One run throws exceptions for every xlInsideVertical line. The other throws exceptions for every xlInsideHorizontal. Finally, a third run completes with no exceptions at all.

至于我可以告诉 Excel 认为这是正常的行为，因为我克隆由excel的宏生成器构建的VB代码，而不是由一个人生成的VB代码。这可能是一个错误的假设，当然。

As far as I can tell Excel considers this normal behavior, because I'm cloning the VB code built by excel's macro generator, not VB code produced by a person. This might be an erroneous assumption, of course.

它将函数与每一行包装在一个尝试，除了块我只是想要更短，更明显，因为20行包裹

It will function with each line wrapped in a try except block I just wanted something shorter and more obvious, because 20 lines wrapped in their own try catch loops is just asking for trouble later.

Update2 ：

这是用于测试的已擦除的CSV文件： gist文件

This is a scrubbed CSV file for testing: gist file

结论：

Vsekhar提供的答案是完美的。它抽象化了异常抑制，所以后来，如果我有时间，我可以实际处理异常发生时。它还允许记录异常，使它们不会消失，不会停止其他异常，并且小到足以在六个月后轻松管理。

The answer provided by Vsekhar is perfect. It abstracts away the exception suppression, so that later, if and when I have time, I can actually deal with the exceptions as they occur. It also allows for logging the exceptions so they don't disappear, not stopping other exceptions, and is small enough to be easily manageable six months from now.

推荐答案

考虑抽象化抑制。

class Suppressor:
    def __init__(self, exception_type):
        self._exception_type = exception_type

    def __call__(self, expression):
        try:
            exec expression
        except self._exception_type as e:
            print 'Suppressor: suppressed exception %s with content \'%s\'' % (type(self._exception_type), e)
            # or log.msg('...')

然后，注意当前代码的追溯中究竟引发了什么异常，并创建一个Suppressor异常：

Then, note in the traceback of your current code exactly what exception is raised, and create a Suppressor for just that exception:

s = Suppressor(excel.WhateverError) # TODO: put your exception type here
s('excel.Selection.Borders(xlDiagonalDown).LineStyle = xlNone')

执行（所以你的追溯仍然会有帮助），你只是压制你明确打算的异常。其他异常会照常传播。

This way you get line-by-line execution (so your tracebacks will still be helpful), and you are suppressing only the exceptions you explicitly intended. Other exceptions propagate as usual.

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