Re: Pass and return
On Thu, 20 Dec 2012 21:23:58 -0800, iMath wrote: Pass and return Are these two functions the same ? They are neither functions, nor are they the same. Check if they are functions: - can you pass them arguments? - can you assign their result to a target? No. py pass(23) File stdin, line 1 pass(23) ^ SyntaxError: invalid syntax py x = return File stdin, line 1 x = return ^ SyntaxError: invalid syntax Are they the same? Try it with these two functions: def test_pass(): for i in range(100): pass print i def test_return(): for i in range(100): return print i py test_pass() 99 py test_return() py So what are they? They are *statements*, not functions. You cannot pass them arguments, nor do they assign a result to a target on the left hand side of = equals sign. pass is a do-nothing statement. It literally does nothing. return exits a function and sets the return result. It is only legal inside functions and generators, while pass is legal almost anywhere. Normally you say return some_value, but you can leave out the result and Python will return None. If functions get all the way to the bottom without a return statement, they will return None. The example you give: def test(): return The body of the function immediately returns None. But functions return None by default, so you could leave the return statement out. If you do that, you will get a SyntaxError because there is nothing in the body: py def test(): ... ... File stdin, line 3 ^ IndentationError: expected an indented block So if you put a pass statement in, just to satisfy the compiler, you get the same result: def test(): pass Also a function which immediately exists and return None. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Pass and return
Mitya Sirenef msire...@lightbird.net wrote: On 12/21/2012 12:23 AM, iMath wrote: Pass and return Are these two functions the same ? def test(): return def test(): pass From the point of style, of course, the latter is much better because that's the idiomatic way to define a no-op function. With a return, it looks like you might have forgotten to add the value to return or deleted it by mistake. I would say it is *an* idiomatic way to define a no-op function. Another idiomatic way is to use a doc-string as the only body, that way you can also explain why you feel the need for an empty function. -- Duncan Booth http://kupuguy.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Pass and return
On 12/21/2012 03:52 AM, Duncan Booth wrote: Mitya Sirenef msire...@lightbird.net wrote: On 12/21/2012 12:23 AM, iMath wrote: Pass and return Are these two functions the same ? def test(): return def test(): pass From the point of style, of course, the latter is much better because that's the idiomatic way to define a no-op function. With a return, it looks like you might have forgotten to add the value to return or deleted it by mistake. I would say it is *an* idiomatic way to define a no-op function. Another idiomatic way is to use a doc-string as the only body, that way you can also explain why you feel the need for an empty function. That's true, a docstring is preferable in many cases. -m -- Lark's Tongue Guide to Python: http://lightbird.net/larks/ -- http://mail.python.org/mailman/listinfo/python-list
Pass and return
Pass and return Are these two functions the same ? def test(): return def test(): pass -- http://mail.python.org/mailman/listinfo/python-list
Re: Pass and return
On 12/21/2012 12:23 AM, iMath wrote: Pass and return Are these two functions the same ? def test(): return def test(): pass I believe they are the same, but these statements have different meanings in other circumstances, e.g.: Class A(object): pass def test(): if x: return else: # do something In first example, (in a class), return would be invalid. In second example, return would return None from function, pass would result in continuing execution after if/else block. Btw you can use disassemble function to look into what these functions do: def a(): pass def b():return from dis import dis dis(a) 1 0 LOAD_CONST 0 (None) 3 RETURN_VALUE dis(b) 1 0 LOAD_CONST 0 (None) 3 RETURN_VALUE So indeed they should be the same.. -m -- Lark's Tongue Guide to Python: http://lightbird.net/larks/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Pass and return
On 12/21/2012 12:23 AM, iMath wrote: Pass and return Are these two functions the same ? def test(): return def test(): pass From the point of style, of course, the latter is much better because that's the idiomatic way to define a no-op function. With a return, it looks like you might have forgotten to add the value to return or deleted it by mistake. -m -- Lark's Tongue Guide to Python: http://lightbird.net/larks/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Pass and return
On Fri, Dec 21, 2012 at 4:23 PM, iMath redstone-c...@163.com wrote: Pass and return Are these two functions the same ? def test(): return def test(): pass They're different statements, but in this case they happen to accomplish the same thing. The pass statement means do nothing. For instance: while input(Enter 5 to continue: )!=5: pass The return statement means stop executing this function now, and return this value, or None if no value. Running off the end of a function implicitly returns None. So what you have is one function that stops short and returns None, and another that does nothing, then returns None. The functions accomplish exactly the same, as does this: test = lambda: None All three compile to the same short block of code - load the constant None, and return it. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: call python from c - pass and return arrays/lists
Pieter wrote:
Hi all,
I'm trying to call a python function from c. I need to pass an
2D-array to python and the python function returns a 2D-list back to
c. I googled arround and I found how to pass ints/strings/... back and
forth, but didn't find anything on passing arrays.
For an int it's as simple as this:
PyArg_Parse(ret,i#, my_long);
But I hacve no idea how to parse python lists to a c-array?
You return a list, parse that as object, and then work with the
sequence-protocol on them.
UNTESTED:
PyArg_Parse(ret,o, the_list);
if(PySequence_Check(the_list) {
int size = PySequence_Size(the_list);
int *result = malloc(sizof(int) * size);
for(int i = 0; i size; i++) {
PyObject *item = PySequence_GetItem(the_list, i);
if(PyInt_Check(item)) {
result[i] = PyInt_AsLong(item);
} else {
return NULL;
}
}
Diez
--
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call python from c - pass and return arrays/lists
Hi all, I'm trying to call a python function from c. I need to pass an 2D-array to python and the python function returns a 2D-list back to c. I googled arround and I found how to pass ints/strings/... back and forth, but didn't find anything on passing arrays. For an int it's as simple as this: PyArg_Parse(ret,i#, my_long); But I hacve no idea how to parse python lists to a c-array? thanks a lot, Pieter -- Pieter Cogghe Ganzendries 186 9000 Gent 0487 10 14 21 -- http://mail.python.org/mailman/listinfo/python-list
Re: call python from c - pass and return arrays/lists
Thanks, this did the trick:
PyArg_Parse(ret,O, the_list);
if (PySequence_Check(the_list)) {
int size = PySequence_Size(the_list);
int *result = malloc(sizeof(int) * size);
int i;
for (i = 0; i size; i++) {
PyObject *item = PySequence_GetItem(the_list, i);
if(PyInt_Check(item)) {
result[i] = PyInt_AsLong(item);
printf(value %d: %d, i, result[i]);
} else {
printf(Didn't work, NO INT);
}
}
}
kind regards,
Pieter
-- Doorgestuurd bericht --
From: Diez B. Roggisch [EMAIL PROTECTED]
To: python-list@python.org
Date: Thu, 10 Apr 2008 12:23:56 +0200
Subject: Re: call python from c - pass and return arrays/lists
Pieter wrote:
Hi all,
I'm trying to call a python function from c. I need to pass an
2D-array to python and the python function returns a 2D-list back to
c. I googled arround and I found how to pass ints/strings/... back and
forth, but didn't find anything on passing arrays.
For an int it's as simple as this:
PyArg_Parse(ret,i#, my_long);
But I hacve no idea how to parse python lists to a c-array?
You return a list, parse that as object, and then work with the
sequence-protocol on them.
UNTESTED:
PyArg_Parse(ret,o, the_list);
if(PySequence_Check(the_list) {
int size = PySequence_Size(the_list);
int *result = malloc(sizof(int) * size);
for(int i = 0; i size; i++) {
PyObject *item = PySequence_GetItem(the_list, i);
if(PyInt_Check(item)) {
result[i] = PyInt_AsLong(item);
} else {
return NULL;
}
}
Diez
--
Pieter Cogghe
Ganzendries 186
9000 Gent
0487 10 14 21
--
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