Re: Pipe in the return statement
Ethan Furman wrote: Billy Mays wrote: On 07/25/2011 10:16 AM, Archard Lias wrote: On Jul 25, 2:03 pm, Ian Collinsian-n...@hotmail.com wrote: On 07/26/11 12:00 AM, Archard Lias wrote: Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement|statement ?? It's simply a bitwise OR. Yes, but how does it get determined, which one actually gets returned? The return statement returns a single value from a function context. The pipe operator takes 2 values and bitwise ORs* them together. That result is then returned to the caller. Just for completeness, if the actual line had been return statement1 or statement2 then Python would compute statement1, and if its boolean value was True would return the computation of statement1, otherwise it would compute statement2 and return that. When 'or' is used, the first truthy* item is return, or the last falsey* item if none evaluate to True. Hence *bitwise* OR (as Billy wrote), _not_ logical OR (as you wrote), probably. -- PointedEars Bitte keine Kopien per E-Mail. / Please do not Cc: me. -- http://mail.python.org/mailman/listinfo/python-list
Pipe in the return statement
Hi,
I have come across something I don't really understand and would be
grateful if someone could shed some light into my understanding of it.
In the documentation of the Qt4 libs in the page regarding the
QAbstractTableModel you find, to make the table editable, the
following:
Qt::ItemFlags StringListModel::flags(const QModelIndex index) const
{
if (!index.isValid())
return Qt::ItemIsEnabled;
return QAbstractItemModel::flags(index) | Qt::ItemIsEditable;
}
Now I'm working with PySide, the Python bindings from Nokia and I
figured the
return in the function to be related with a parent
(QAbstractItemModel)
followed by the actual Flag that says: yes the item, the index is
pointing
at, is actually editable. So translation of the C++ to Python would
be, and
it actually worked:
def flags(self, index):
if not index.isValid():
return Qt.ItemIsEnabled
return super(self.__class__, self).flags(index) |
Qt.ItemIsEditable
Still I dont get how I am supposed to understand the pipe and its task/
idea/influece on control flow, of:
return statement | statement
??
Thankful if you could help me with this.
Kind regards,
Archard Lias
--
http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On 07/26/11 12:00 AM, Archard Lias wrote: Hi, Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement |statement ?? It's simply a bitwise OR. -- Ian Collins -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
Am 25.07.2011 14:00, schrieb Archard Lias: def flags(self, index): if not index.isValid(): return Qt.ItemIsEnabled return super(self.__class__, self).flags(index) | Your use of super() is incorrect and will not work as you might expect. You *must* use the class here, never self.__class__. Christian -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: return statement | statement In the words of René Magritte, return statement | statement ^ Ceci n'est pas une pipe. -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 1:52 pm, TonyO guinness.t...@gmail.com wrote: return statement | statement In the words of René Magritte, return statement | statement ^ Ceci n'est pas une pipe. *golf clap* -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 2:03 pm, Ian Collins ian-n...@hotmail.com wrote: On 07/26/11 12:00 AM, Archard Lias wrote: Hi, Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement |statement ?? It's simply a bitwise OR. -- Ian Collins Yes, but how does it get determined, which one actually gets returned? -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On 07/25/2011 10:16 AM, Archard Lias wrote: On Jul 25, 2:03 pm, Ian Collinsian-n...@hotmail.com wrote: On 07/26/11 12:00 AM, Archard Lias wrote: Hi, Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement|statement ?? It's simply a bitwise OR. -- Ian Collins Yes, but how does it get determined, which one actually gets returned? The return statement returns a single value from a function context. The pipe operator takes 2 values and bitwise ORs* them together. That result is then returned to the caller. The pipe character in this instance is not the same as in a shell. * This is not exactly true, but don't worry about it. -- Bill -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
Hello Archard, On 25.07.2011, at 16:16, Archard Lias wrote: On Jul 25, 2:03 pm, Ian Collins ian-n...@hotmail.com wrote: On 07/26/11 12:00 AM, Archard Lias wrote: Hi, Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement |statement ?? It's simply a bitwise OR. -- Ian Collins Yes, but how does it get determined, which one actually gets returned? You do a Bitwise OR with numbers. Your statements are both returning numbers and those are combined with a bitwise OR. Combining b0001 with b0010 results in 0011 for example, you can see this very often done in C Code to set and check flags. Here is a gentle introduction: http://www.codeproject.com/KB/tips/Binary_Guide.aspxhttp://www.codeproject.com/KB/tips/Binary_Guide.aspx Cheers Oliver -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
In 1c175da2-79f4-40ed-803f-217dc935d...@m8g2000yqo.googlegroups.com Archard Lias archardl...@googlemail.com writes: return statement | statement It's simply a bitwise OR. Yes, but how does it get determined, which one actually gets returned? Neither value is returned on its own; the bitwise OR of both values is computed and that value is returned. It seems that you don't understand what the term bitwise or means. Perhaps a Google search might help. -- John Gordon A is for Amy, who fell down the stairs gor...@panix.com B is for Basil, assaulted by bears -- Edward Gorey, The Gashlycrumb Tinies -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 3:16 pm, Archard Lias archardl...@googlemail.com wrote: Yes, but how does it get determined, which one actually gets returned? It's a bit-wise or, not a logical or so what get returns is a combination of the two results. The n-th bit of the return value is 1 if the n-th bit of either (or both) of the two statements (Fixed width font) a 1 1 0 0 0 1 1 1 0 0 1 0 1 ... b 0 1 0 1 0 0 1 0 0 0 0 1 1 ... a|b 1 1 0 1 0 1 1 0 0 0 1 1 1 ... (/Fixed width font) -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 4:39 pm, John Gordon gor...@panix.com wrote: In 1c175da2-79f4-40ed-803f-217dc935d...@m8g2000yqo.googlegroups.com Archard Lias archardl...@googlemail.com writes: return statement | statement It's simply a bitwise OR. Yes, but how does it get determined, which one actually gets returned? Neither value is returned on its own; the bitwise OR of both values is computed and that value is returned. It seems that you don't understand what the term bitwise or means. Perhaps a Google search might help. -- John Gordon A is for Amy, who fell down the stairs gor...@panix.com B is for Basil, assaulted by bears -- Edward Gorey, The Gashlycrumb Tinies It figures, that you are right :P. -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 4:35 pm, Oliver Bestwalter oli...@bestwalter.de wrote: Hello Archard, On 25.07.2011, at 16:16, Archard Lias wrote: On Jul 25, 2:03 pm, Ian Collins ian-n...@hotmail.com wrote: On 07/26/11 12:00 AM, Archard Lias wrote: Hi, Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement |statement ?? It's simply a bitwise OR. -- Ian Collins Yes, but how does it get determined, which one actually gets returned? You do a Bitwise OR with numbers. Your statements are both returning numbers and those are combined with a bitwise OR. Combining b0001 with b0010 results in 0011 for example, you can see this very often done in C Code to set and check flags. Here is a gentle introduction: http://www.codeproject.com/KB/tips/Binary_Guide.aspxhttp://www.codepr... Cheers Oliver Oh!, never gave it a thought about the fact that what I was looking at where flags... Thank you very much for the link, is a great introduction to something I had not known before. -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 2:33 pm, Christian Heimes li...@cheimes.de wrote: Am 25.07.2011 14:00, schrieb Archard Lias: def flags(self, index): if not index.isValid(): return Qt.ItemIsEnabled return super(self.__class__, self).flags(index) | Your use of super() is incorrect and will not work as you might expect. You *must* use the class here, never self.__class__. Christian It would be great if you could elaborate a little more on that. Am I not supposed to access the parent here? -- Archard -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
Am 25.07.2011 17:28, schrieb Archard Lias: It would be great if you could elaborate a little more on that. Am I not supposed to access the parent here? You must spell out the parent explicitly, otherwise subclasses call super() with themselves rather than the correct parent class. self.__class__ is too dynamic here. Have a look at this example: class A(object): def method(self): pass class B(A): def method(self): super(self.__class__, self).method() class C(B): pass In this example, C().method() results in super(C, self).method() because self.__class__ is C. However that is wrong because you have to call super() with the direct parent. Christian -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On 25 Jul., 18:11, Christian Heimes li...@cheimes.de wrote: Am 25.07.2011 17:28, schrieb Archard Lias: It would be great if you could elaborate a little more on that. Am I not supposed to access the parent here? You must spell out the parent explicitly, otherwise subclasses call super() with themselves rather than the correct parent class. self.__class__ is too dynamic here. Have a look at this example: class A(object): def method(self): pass class B(A): def method(self): super(self.__class__, self).method() class C(B): pass In this example, C().method() results in super(C, self).method() because self.__class__ is C. However that is wrong because you have to call super() with the direct parent. Christian Oh! Get it, thanks a lot :P -- Archard -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
Billy Mays wrote: On 07/25/2011 10:16 AM, Archard Lias wrote: On Jul 25, 2:03 pm, Ian Collinsian-n...@hotmail.com wrote: On 07/26/11 12:00 AM, Archard Lias wrote: Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: returnstatement|statement ?? It's simply a bitwise OR. Yes, but how does it get determined, which one actually gets returned? The return statement returns a single value from a function context. The pipe operator takes 2 values and bitwise ORs* them together. That result is then returned to the caller. Just for completeness, if the actual line had been return statement1 or statement2 then Python would compute statement1, and if its boolean value was True would return the computation of statement1, otherwise it would compute statement2 and return that. When 'or' is used, the first truthy* item is return, or the last falsey* item if none evaluate to True. -- None or 2 or 0 2 -- None or 2 or 3 2 -- None or [] or 0 0 With 'and', the first falsey item is returned, unless all the items are truthy in which case the last item is returned: -- 2 and 3 3 -- 2 and 0 and 9 0 Hope this helps. ~Ethan~ * 'truthy' = bool(some expression or object) == True * 'falsey' = bool(some expression or object) == False -- http://mail.python.org/mailman/listinfo/python-list
Re: Pipe in the return statement
On Jul 25, 5:52 am, TonyO guinness.t...@gmail.com wrote: Still I dont get how I am supposed to understand the pipe and its task/ idea/influece on control flow, of: return statement | statement In the words of René Magritte, return statement | statement ^ Ceci n'est pas une pipe. We have a WINNER!! -- http://mail.python.org/mailman/listinfo/python-list
