CODEWITHSUNDEEP
python
Ecanales
Ecanales

Reputation: 81

Is there a way to feed a python script a command if it crashes at any point?

I am familiar with try, except. However I'm looking for a more general method that just runs a simple command before the script stops running after any error is raised.

For example if I'm using xlsxwriter:

import xlsxwriter
wb = xlssxwriter.Workbook
ws = wb.add_worksheet()
for i in range (len(list)):
    ws.write(i,0,"Hello World!")

#If this script fails, run ws.close()

Upvotes: 2

Views: 96

Answers (3)

akoeltringer
akoeltringer

Reputation: 1721

This is what context managers are for (the with statement). The Workbook class actually provides what is necessary.

It is as simple as

with xlsxwriter.Workbook('hello_world.xlsx') as workbook:
    worksheet = workbook.add_worksheet()
    [...]

See Workbook documentation

In case you want to do other things as well, the try ... except ... else ... finally statement(s) are what you need. See documentation

Upvotes: 3

ShadowRanger
ShadowRanger

Reputation: 155536

For the specific case of calling a close method (where the object doesn't support the context management protocol natively, so you can't use it bare in a with statement), you can improve a bit on try/finally by using contextlib.closing to wrap it such that it's with statement compatible, replacing your code:

ws = wb.add_worksheet()
for i in range (len(list)):
    ws.write(i,0,"Hello World!")

with (adding import contextlib to the top of your file):

with contextlib.closing(wb.add_worksheet()) as ws:
    for i in range(len(list)):
        ws.write(i,0,"Hello World!")

That calls close unconditionally when the block is exited, whether by exception, return, or just naturally leaving the block without error or returning (which is usually what you want). If for some reason you only want to call it when you have an exception, you can do:

ws = wb.add_worksheet()
try:
    for i in range (len(list)):
        ws.write(i,0,"Hello World!")
except:  # Okay to use bare except because we re-raise after cleanup
    ws.close()
    raise  # Re-raise whatever exception led us here now that cleanup is done

That will only close when an exception occurs, and will reraise the exception (because continuing silently in this scenario is probably wrong).

Upvotes: 2

Joonatan Samuel
Joonatan Samuel

Reputation: 651

Well. In general this is solved by:

try:
     code that produces error
finally:
     cleanup()

Upvotes: 0

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