matplotlib-devel Mailing List for matplotlib

Steve,

I am aware of the caveats associated with the "name" attribute, which  
is why the code I sent you attempts to do the right thing when it  
doesn't exist.  I hadn't considered the case of stdout, but you could  
probably detect situations like that by testing to see if the  
extension is the empty string:

> 	# figure out what the format is
> 	if extension is None or extension == '':
> 		...

However, this variety of special case handling could make things more  
confusing for beginning users.  I think ultimately you should do  
whatever you think strikes the best balance between convenience and  
clarity.

On Jul 21, 2006, at 7:27 PM, Steven Chaplin wrote:
>
> I think an explicit 'format' argument is better than reading a 'name'
> attribute which only works sometimes.

In general I tend to agree with you, but I'd like to see Just Work  
when writing to an open file.  I don't have a lot of stake in this  
either way, since I spend most of my time with matplotlib pushing the  
RGB data onto wxPython widgets.

Ken

On Fri, 2006-07-21 at 17:21 -0500, Ken McIvor wrote:
> On Jul 20, 2006, at 7:53 AM, Steven Chaplin wrote:
> >
> > However, print_figure() does not support writing to file objects in
> > different formats because it only takes a 'filename' argument and  
> > does not
> > have an argument to allow you to specify the format.
> 
> You can usually get the filename from the "name" attribute of a file- 
> like object.  Below is some untested pseudo-Python code that will use  
> the value of "format" if it's specified and will otherwise try to  
> pull the format from the file name.  You should be able to collapse  
> the nested if/else structure -- I've covered all four permutations  
> explicitly for clarity.
> 
> I'm too swamped to put a lot of time into this code/explanation, so  
> please let me know if this doesn't make any sense.
> 
> Ken
> 
> 
> def print_figure(self, fileOrString, format=None):
> 	extension = None
> 
> 	if is_file_like(fileOrString):
> 		filename = getattr(fileobj, 'name', None)
> 	else:
> 		filename = fileOrString
> 
> 	if filename is not None:
> 		# get the extension and make it all lower-case
> 		extension = os.path.splitext(filename, None)
> 
> 	# figure out what the format is
> 	if extension is None:
> 		# no name file, so use format
> 		if format is None:
> 			raise ValueError('you must specify a format')
> 		else:
> 			pass # use the value of "format"				else:
> 		# there's a name, but the format keyword overrides it
> 		if format is None:
> 			# use the file extension
> 			format = extension
> 		else:
> 			pass # use the value of "format"
> 
> 	format = format.lower()
> 	if format not in ('png', 'ps', 'svg'):
> 		raise ValueError('invalid file format %r' % (format,))
> 
> 	# At this point in the method, "format" is the requested file format.

The 'name' attribute is only useful sometimes:
 - it works for file objects (but only when the filename ends with a
format extension)
 - it does not work for sys.stdout, StringIO or cStringIO file-like
objects
I think an explicit 'format' argument is better than reading a 'name'
attribute which only works sometimes.

Steve

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