[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-23 Thread tb 

tb added the comment:

This is my use case:
I am creating a custom DictReader class for reading and accessing the columns 
white space and case insensitive. 
For this I created a dict subclass (DictInsensitive) with a custom __getitem__ 
method. DictReaderInsensitive.__next__ overrides the original 
DictReader.__next__ by returning a DictInsensitive. I also override the 
DictReader.fieldnames property to lower/strip all fieldnames.
See http://stackoverflow.com/a/12970460/1251007 for an example. 
This is all functional with the current csv.DictReader. All entries in 
DictReaderInsensitive.fieldnames are in lower case and without white space and 
by iterating over the lines I get dictionaries where I can access the keys 
white space/case insensitive.

Now, the problem is: If I want the check wether a specific fieldname is present 
in the input file, I have strip()/lower() by hand:
csv_in = DictReaderInsensitive(open(input_file, 'rU'))
if Fieldname to check.strip().lower() in csv_in.fieldnames

To do this automatically, I created a ListInsensitive as a subclass of list:
class ListInsensitive(list):
def __contains__(self, item):
return list.__contains__(self, item.strip().lower())

Now I want csv.DictReader to use that new class. I thought of overwriting the 
setter method, but here lies the current problem. I can overwrite the setter 
method, but csv.DictReader does not use the setter method internally.

My setter method looks like this:
@fieldnames.setter
def fieldnames(self, value):
if value == None:
self._fieldnames = None
else:
self._fieldnames = ListInsensitive()
for name in value:
self._fieldnames.append(name.strip().lower())

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[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-23 Thread Serhiy Storchaka 

Serhiy Storchaka added the comment:

You can overwrite fieldnames getter.

@property
def fieldnames(self):
if self._fieldnames is None:
try:
self._fieldnames = next(self.reader)
except StopIteration:
pass
self.line_num = self.reader.line_num
if not isinstance(self._fieldnames, ListInsensitive):
self._fieldnames = ListInsensitive(name.strip().lower() for name in 
self._fieldnames)
return self._fieldnames

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nosy: +serhiy.storchaka

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[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-23 Thread tb 

tb added the comment:

Okay, that makes my use case obsolete. Overwriting the getter method like this 
seems obvious ... Somehow this hasn't come to my mind.

Sorry for bothering. From my point of view, we can close this issue. Or is 
there another use case?

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[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-23 Thread R. David Murray 

R. David Murray added the comment:

It does seem more logical to implement this in the getter, now that Serhiy has 
pointed it out :)  So let's close this.

(Aside: if it were me, I'd move the mangling of the fieldnames into the 
ListInsensitive __init__ method.)

--
resolution:  - invalid
status: open - closed

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[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-22 Thread Ramchandra Apte 

Changes by Ramchandra Apte maniandra...@gmail.com:


--
title: small fix to csv.DictReader.__init__ - make csv.DictReader.__init__ use 
self.fieldnames

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[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-22 Thread Berker Peksag 

Berker Peksag added the comment:

I think this is an invalid request.

See the usage of property decorator: 
http://docs.python.org/py3k/library/functions.html#property

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[issue16297] make csv.DictReader.__init__ use self.fieldnames

2012-10-22 Thread R. David Murray 

R. David Murray added the comment:

I think it is not an invalid request.  However, what is the use case?  Normally 
a class will manipulate the real variable, and the getter/setter is the 
public API.  Without a good use case it doesn't seem worth changing that bit of 
the init method.

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