![]() ![]() Examples include required files, and simple locking. This is described in more detail here and here.Īs a general guideline, with statements excel for cases where exceptions are not expected, and the default "enter/open/acquire" behaviour is adequate. ![]() There was a suggestion to add exception handling to this effect on the mailing list: with open(.) as file:įinally it's worth noting that you can directly enter and exit context managers like so: file = open(.)._enter_() try:Īs unfortunately verbose as this is, the with statement doesn't allow you to catch exceptions thrown during its evaluation. It's best practice to catch exceptions as close to the point they're thrown to avoid catching unrelated exceptions of the same type. ![]() In the example you give, it's not better. os.walk) it is very very easy to run out of file handles if code relying on refcount semantics is run on a VM with different behaviour. Jython, IronPython and PyPy all have non-refcount semantics, and there's nothing preventing CPython from going the other way (though it's highly unlikely for the immediate future). For example, it's also used with decimal to establish a decimal context for a particular block of code.įinally (responding to your comment to the previous answer) you should never rely on refcount semantics for handling resources in Python. The second is (as stated in another answer) that you can't forget to call f.close().īTW, the term is "context management", not "resource management" - the with statement manages contexts, some of which may be resources, but others not. Your second example similarly is wrong, and should be structured like: try:ĭo_other_stuff_when_it_we_have_file_IO_problems() (note - no need for an except clause if you've got nothing to do there). PHP has had support for the exception handling for ages however, comparing it to Java, this support was pretty weak. The correct structure (equivalent to the with) is: f = open(my_file) The way you've structured it, if an exception is thrown while trying to open the file then you will never bind an open file to the name f, leading to either a NameError in the finally clause (if f has never been bound within scope) or something entirely unexpected (if it has). For a start, it helps prevent the problem you've introduced in your try. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |