Re: What's the tidy/elegant way to protect this against null/empty parameters?
- Original Message - I want to fix an error in some code I have installed, however I don't really want to just bodge it. The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. So, what's the neatest way to protect the get_text() method from empty data? -- Chris Green -- http://mail.python.org/mailman/listinfo/python-list Hi Chris, Usually, you want to keep your variable types consistent. For instance, if node.tags is supposed to be a string, then make it so that it is always a string. However NoneType may be one inconsistent type that is acceptable for any variable. It depends on the situation, and your personal preferences. To go back to your example, None may have a different meaning that an empty string. Here's a way to redefine locally a None object into an empty string: , .join(node.tags or '') if node itself can be None, here's a way to protect against None attribute access: , .join(node and node.tags) you can combine the 2 methods: , .join((node and node.tags) or '') This method uses the fact that: A and B returns B if bool(A) and bool(B) are True, returns the first non True between A and B. A or B returns B if bool(A) is False, returns A if bool(A) is True. JM -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
On Monday, October 15, 2012 1:33:02 PM UTC+2, (unknown) wrote: I want to fix an error in some code I have installed, however I don't really want to just bodge it. The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. So, what's the neatest way to protect the get_text() method from empty data? -- Chris Green Hi, Instead of protecting against empty data, you could just catch the exception, issue a warning and return a default error node which is valid. So something like (not tested): def get_text(self, idx): # override ! node = self.items[idx] error_a = A valid, but erroneous representation of a try: a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] except TypeError: print 'Oops, something went wrong' a = error_a # You should always have a valid a here (or another exception has occured) return a -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
Marco Nawijn naw...@gmail.com wrote: On Monday, October 15, 2012 1:33:02 PM UTC+2, (unknown) wrote: I want to fix an error in some code I have installed, however I don't really want to just bodge it. The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. So, what's the neatest way to protect the get_text() method from empty data? -- Chris Green Hi, Instead of protecting against empty data, you could just catch the exception, issue a warning and return a default error node which is valid. So something like (not tested): def get_text(self, idx): # override ! node = self.items[idx] error_a = A valid, but erroneous representation of a try: a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] except TypeError: print 'Oops, something went wrong' a = error_a # You should always have a valid a here (or another exception has occured) return a That sounds like a reasonable approach, thank you (and all the other ideas). -- Chris Green -- http://mail.python.org/mailman/listinfo/python-list
What's the tidy/elegant way to protect this against null/empty parameters?
I want to fix an error in some code I have installed, however I don't really want to just bodge it. The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. So, what's the neatest way to protect the get_text() method from empty data? -- Chris Green -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
tinn...@isbd.co.uk writes: I want to fix an error in some code I have installed, however I don't really want to just bodge it. ... Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. That means you do really want to just bodge it, doesn't it? (I'm reading bodge as something like kludge but maybe it means something different.) So, what's the neatest way to protect the get_text() method from empty data? I'd say the use of None as a picture is already a code smell: figure out where it is coming from, and fix it. Or, if you want to just bodge it (by checking for None and returning the empty string or something)), then try it and see if it helps. I'm assuming this is something noncritical that you're running on your own computer for convenience. I wouldn't ship code to a customer without a more careful fix. -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
On Mon, Oct 15, 2012 at 4:23 AM, tinn...@isbd.co.uk wrote: I want to fix an error in some code I have installed, however I don't really want to just bodge it. bodge. Well, I learned a new word this morning! The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, To be precise: when node.tags contains one or more `None`s (Python's equivalent of what other languages call null or nil). That's what the traceback is saying. you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) Ah, so this is apparently regarding https://code.google.com/p/jbrout/ . Would have been nice not to have had to search and then only locate it indirectly. Something to consider next time you write in... Make sure you report your bug upstream! File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. So, what's the neatest way to protect the get_text() method from empty data? Filter out the `None`s with a generator expression: , .join(tag for tag in node.tags if tag is not None), Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
In article 1b8tk9-un9@chris.zbmc.eu, tinn...@isbd.co.uk wrote: The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found Now its *probably* something higher up the tree causing the problem (it's only one particular image in 20 thousand or so that breaks things) but I really want to just get things working. So, what's the neatest way to protect the get_text() method from empty data? Well, you don't describe what get_text() is supposed to return First, you build a list of what I'm guessing are all strings, then you index into it and return one of the values. So, I'm guessing get_text() is supposed to return a string. At a low level, you can certainly fix that by testing to see if self.items[idx] returns what you're expecting (an instance of Node?) and returning an empty string if it's not: def get_text(self, idx): # override ! node = self.items[idx] if not node: return a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a Whether that makes sense in your program, I have no idea. What does it mean for node to be empty? Is this a normal occurrence? If so, then your code needs to deal with properly (the suggest above being just one possible way). Or, is it impossible for node to be empty? In that case, that fact that it *is* empty is a bug, and the above suggestion will just hide the bug for one more level and make it that much harder to figure out what's really going on. What you might really want to do is sprinkle your code with assert node statements. This will force your program to crash and burn the first time node is empty, which might help you figure out why it is. -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
I want to fix an error in some code I have installed, ... Apart from all the reasons why it's bad (see the Python Zen #10). One way to do it is: return [i or '' for i in a] -- http://mail.python.org/mailman/listinfo/python-list
Re: What's the tidy/elegant way to protect this against null/empty parameters?
On 10/15/2012 7:23 AM, tinn...@isbd.co.uk wrote: I want to fix an error in some code I have installed, however I don't really want to just bodge it. The function producing the error is:- def get_text(self, idx): # override ! node = self.items[idx] a= [ , .join(node.tags), node.comment, node.folderName, cd2rd(node.date), node.name, '[' + self.rating_stars[node.rating] + ']' ] [self.select] return a The error occurs when node[] (or at least its members) turn out to be empty, This is not the problem. you get a Traceback that ends with:- File /usr/lib/jbrout/jbrout/listview.py, line 608, in draw_cell layout.set_text(self.get_text(thumbnail_num)) File /usr/lib/jbrout/jbrout.py, line 325, in get_text , .join(node.tags), TypeError: sequence item 0: expected string, NoneType found The specific problem is that node.tags is supposed to be a sequence of strings and somehow one instead has None as the first, and probably last item. This was likely intended to indicate an empty list, but the way to do that is to have a empty list, which would have worked just fine. In other words, the likely problem is that node.tags is *not* an empty sequence when it should be. ','.join([None]) Traceback (most recent call last): File pyshell#9, line 1, in module ','.join([None]) TypeError: sequence item 0: expected str instance, NoneType found ','.join([]) '' -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
