error handling when opening files

wxjmfauth at gmail.com wxjmfauth at gmail.com
Tue Jul 8 11:38:42 CEST 2014


Alex is right (at least not wrong) and I'm also working
in a similar way.

- If there is a problem in opening, the file is never
opened and only an IOError can happen.
- If do_stuff succeeds: the file is open and will be closed
because of the with statement.
- If do_stuff does not succeed (errors), the file will be
closed (with statement) and only later the error is raised.
Tricky, but it works like this.

In short: simple and elegant solution.

>>> def z():
...     try:
...         with open('eta.cfg', 'r') as f:
...             a = 1 / 0
...     except IOError:
...         print('error in opening file')
...     except ZeroDivisionError:
...         print('ZeroDivisionError', f.closed)
...         
>>> z()
ZeroDivisionError True
>>> def z2():
...     try:
...         with open('xxx.cfg', 'r') as f:
...             a = 1 / 0
...     except IOError:
...         print('error in opening file')
...     except ZeroDivisionError:
...         print('ZeroDivisionError', f.closed)
...         
>>> z2()
error in opening file
>>> def z3():
...     try:
...         with open('xxx.cfg', 'r') as f:
...             a = 1 / 0
...     except IOError:
...         print('error in opening file')
...         print(f.closed)
...     except ZeroDivisionError:
...         print('ZeroDivisionError', f.closed)
...         
>>> z3()
error in opening file
Traceback (most recent call last):
  File "<eta last command>", line 1, in <module>
  File "<eta last command>", line 7, in z3
UnboundLocalError: local variable 'f' referenced before assignment

----

One could consider a case where do_stuff is opening a file...

----

Quote: "Interestingly, did you know that even *closing* "
a file can fail? 

Answer: Does "with" fail? I never explicitely closed the file.




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