[issue44366] Define functions without parentheses (if no parameters given)

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

Closing as this would obviously need a PEP, please open a discusion first on 
python-ideas

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resolution:  -> rejected
stage:  -> resolved
status: open -> closed

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[issue44366] Define functions without parentheses (if no parameters given)

[Irit Katriel]

Irit Katriel  added the comment:

The python-ideas mailing list is a better place for such questions than the bug 
tracker.

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[issue44366] Define functions without parentheses (if no parameters given)

[Boštjan Mejak]

New submission from Boštjan Mejak :

The syntax to define a class looks like this:

class MyClass:
pass

Nice and neat.

***
And the syntax to define a function looks like this:

def my_function():
pass

Hmmm...

***
What if we could define functions (that don't have any parameters) like this:

def my_function:
pass

***
Is that a possible scenario at this point, or even desirable?

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components: Interpreter Core
messages: 395436
nosy: PedanticHacker
priority: normal
severity: normal
status: open
title: Define functions without parentheses (if no parameters given)
type: enhancement
versions: Python 3.11

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Re: functions without parentheses

[phil hunt]

On Fri, 29 Jul 2005 06:37:52 GMT, Bengt Richter [EMAIL PROTECTED] wrote:

I suggested in a previous thread that one could support such a syntax by
supporting an invisible binary operator between two expressions, 

That's a truely appalling idea.

so that
examine string translates to examine.__invisbinop__(string) if
examine as an expression evaluates to an object that has a __invisbinop__ 
method.

Then you wouldn't define examine as a function, you would define it as an 
instance
of a class like
class Examine(object):
define __invisbinop__(self, other):
#...whatever
examine = Examine()
and then
examine string

Pass the sick bucket.

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Re: functions without parentheses

[Bengt Richter]

On Fri, 29 Jul 2005 20:54:42 +1000, Steven D'Aprano [EMAIL PROTECTED] wrote:

On Fri, 29 Jul 2005 06:37:52 +, Bengt Richter wrote:

 I suggested in a previous thread that one could support such a syntax by
 supporting an invisible binary operator between two expressions, so that
 examine string translates to examine.__invisbinop__(string) if
 examine as an expression evaluates to an object that has a __invisbinop__ 
 method.

Why would you want to?

Mainly to say that I think there is way to do it (and thus further to mulch the 
idea garden ;-)
whatever the merits. As to the merits, I haven't thought about it much, but 
ISTM for limited
contexts it would allow you to spell concatenating/aggregating expressions 
without the
line noise of intervening operator glyphs, e.g.,

agg = Aggregate() first_thing second_thing 3 four etc.and.so.forth ;
or

   mypath = Path() prefix middle filename+'.ext' ; # explicit terminating ';' 
or (...) might be needed
   # if EOL can be part of 
whitespace delim as below

or
arr = (ArrayElementAggregator()
 11 12 13
 21 22 23
  )


The latter presupposes that white-space including an EOL causes attempt to 
access an alternate
__invisbinop__ (e.g., __invisbinopNL__) that one could define to aggregate new 
rows of expressions,
but would not be an error if absent, and thus end a single-line aggregator 
without explict ';' or parens.

I haven't thought of all the ramifications, I was just playing with the idea ;-)

Others might think of other ways to answer your why ;-)

Regards,
Bengt Richter
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Re: functions without parentheses

[Bengt Richter]

On Sat, 30 Jul 2005 08:14:16 +0100, [EMAIL PROTECTED] (phil hunt) wrote:

On Fri, 29 Jul 2005 06:37:52 GMT, Bengt Richter [EMAIL PROTECTED] wrote:

I suggested in a previous thread that one could support such a syntax by
supporting an invisible binary operator between two expressions, 

That's a truely appalling idea.

so that
examine string translates to examine.__invisbinop__(string) if
examine as an expression evaluates to an object that has a __invisbinop__ 
method.

Then you wouldn't define examine as a function, you would define it as an 
instance
of a class like
class Examine(object):
define __invisbinop__(self, other):
#...whatever
examine = Examine()
and then
examine string

Pass the sick bucket.

LOL ;-)

Regards,
Bengt Richter
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Re: functions without parentheses

[Dan Sommers]

On Sat, 30 Jul 2005 18:42:59 GMT,
[EMAIL PROTECTED] (Bengt Richter) wrote:

 or
 arr = (ArrayElementAggregator()
  11 12 13
  21 22 23
   )

What was that again about every other computer language wanting to be
Lisp?  ;-)

Regards,
Dan

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Re: functions without parentheses

[Bengt Richter]

On Thu, 28 Jul 2005 00:59:51 -0700 (PDT), Jerry He [EMAIL PROTECTED] wrote:

Hi, 
  Is it possible to create a function that you can use
without parenthesizing the arguments? for example, for

def examine(str):
 .
 .

Is there some way to define it so that I can call it
like

examine string 
instead of examine(string)? 

I suggested in a previous thread that one could support such a syntax by
supporting an invisible binary operator between two expressions, so that
examine string translates to examine.__invisbinop__(string) if
examine as an expression evaluates to an object that has a __invisbinop__ 
method.

Then you wouldn't define examine as a function, you would define it as an 
instance
of a class like
class Examine(object):
define __invisbinop__(self, other):
#...whatever
examine = Examine()
and then
examine string

Of course this is a strange syntax mod to the language, and undoubtedly
would have many strange effects, but superficially, it seems like something
could be done. But a consequence of white space as potential invisible operator
would be that foo() and foo () might be foo.__call__() vs foo.__invisbinop_(())

Regards,
Bengt Richter
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Re: functions without parentheses

[Steven D'Aprano]

On Fri, 29 Jul 2005 06:37:52 +, Bengt Richter wrote:

 I suggested in a previous thread that one could support such a syntax by
 supporting an invisible binary operator between two expressions, so that
 examine string translates to examine.__invisbinop__(string) if
 examine as an expression evaluates to an object that has a __invisbinop__ 
 method.

Why would you want to?



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Re: functions without parentheses

[Josef Meile]

Steven D'Aprano wrote:
 On Fri, 29 Jul 2005 06:37:52 +, Bengt Richter wrote:
 
 
I suggested in a previous thread that one could support such a syntax by
supporting an invisible binary operator between two expressions, so that
examine string translates to examine.__invisbinop__(string) if
examine as an expression evaluates to an object that has a __invisbinop__ 
method.
 
 
 Why would you want to?
 
My best guest is that the OP uses VB, where you can do that. I
personally hate this feature because it just makes me do a lot of
mistakes. ie: In VB you can do:

fooFunction fooParameter

but if you want to assign this to a variable you **must** use this:

fooVer = fooFunction(fooParaMeter)

I really get confused because I automatically use the braces.

Regards,
Josef

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functions without parentheses

[Jerry He]

Hi, 
  Is it possible to create a function that you can use
without parenthesizing the arguments? for example, for

def examine(str):
 .
 .

Is there some way to define it so that I can call it
like

examine string 
instead of examine(string)? 

thanks in advance

-Jerry




Start your day with Yahoo! - make it your home page 
http://www.yahoo.com/r/hs 
 
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Re: functions without parentheses

[Robert Kern]

Jerry He wrote:
 Hi, 
   Is it possible to create a function that you can use
 without parenthesizing the arguments? for example, for
 
 def examine(str):
  .
  .
 
 Is there some way to define it so that I can call it
 like
 
 examine string 
 instead of examine(string)? 

No.

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In the fields of hell where the grass grows high
  Are the graves of dreams allowed to die.
   -- Richard Harter

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RE: functions without parentheses

[Delaney, Timothy (Tim)]

Jerry He wrote:

 def examine(str):
  .
  .
 
 Is there some way to define it so that I can call it
 like
 
 examine string
 instead of examine(string)?

No. Python's syntax does not work that way. Why would you want to? For
more information about this, read:

http://www.catb.org/~esr/faqs/smart-questions.html


You can create properties on classes which call a function when you get,
set or delete them. 

class Test (object):
def _getX (self):
return self.__x

def _setX (self, value):
self.__x = value

x = property(fget=_getX, fset=_setX)

t = Test()
t.x = 1
print t.x

Note that this is almost completely different to what you asked about.

Tim Delaney
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Re: functions without parentheses

[Steven D'Aprano]

On Thu, 28 Jul 2005 00:59:51 -0700, Jerry He wrote:

 Hi, 
   Is it possible to create a function that you can use
 without parenthesizing the arguments?

What problem are you trying to solve that requires this sort of syntax,
and why can't it be solved with parentheses?

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Re: functions without parentheses

[Simon Dahlbacka]

If you actually want that kind of syntax, then why don't you use Visual
Basic? ;)

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Re: functions without parentheses

[Steve Holden]

Simon Dahlbacka wrote [about function calls without parenthesis]:
 If you actually want that kind of syntax, then why don't you use Visual
 Basic? ;)
 
Because Perl is far too tempting to ignore.

The serious answer to the OP's question, however, is that Python refuses 
to guess whether a function reference not followed by a left parenthesis 
is a reference to a function or a reference to the result of calling the 
function. Perl and VB(Script) make more use of context, in ways that 
confuse many users.

Time for someone to try

 import this

regards
  Steve
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Re: functions without parentheses

[bruno modulix]

Simon Dahlbacka wrote:
 If you actually want that kind of syntax, then why don't you use Visual
 Basic? ;)

s/VisualBasic/Ruby/


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Re: functions without parentheses

[Steven Bethard]

Jerry He wrote:
 def examine(str):
  .
  .
 
 Is there some way to define it so that I can call it
 like
 
 examine string 
 instead of examine(string)? 

What do you want to happen when someone types:

 examine

???  Or better yet, what if you do something like:

 map(examine, list_of_strs)

???  Should examine be called with no arguments?  Or should it be passed 
as a function object to map?

STeVe
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Re: functions without parentheses

[gene tani]

http://onestepback.org/index.cgi/Tech/Ruby/PythonAndRuby.rdoc

this blog talks about design differences, e.g. what . means, whether
functions and methods are 1st-class objects.

St

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Re: functions without parentheses

[Scott David Daniels]

Jerry He wrote:
 ... Is there some way to define [examine] so I can call it like
 examine string 
 instead of  examine(string)? 

Perhaps you are looking for ipython (google for it) if
all you are looking for is ease of interactive entry.

--Scott David Daniels
[EMAIL PROTECTED]
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Re: functions without parentheses

[bruno modulix]

Jerry He wrote:
 Hi, 
   Is it possible to create a function that you can use
 without parenthesizing the arguments? for example, for
 
 def examine(str):
  .
  .
 
 Is there some way to define it so that I can call it
 like
 
 examine string 
 instead of examine(string)? 

No.

The reason (well, one of the reasons) is that, given a function my_func

def my_func(*args, **kwargs):
  print in my_func:
  print + args : %s % , .join(args)
  print + kwargs %s % , .join([%s=%s % keyval \
   for keyval in kwargs.items()])
  return True


the expressions

  my_func
and
  my_func()

have very different semantics. (hint: copy/paste this code in your
python interactive interpreter).

The first expression has exactly the same semantic as it would have with
any other object[1] : it returns a reference to the function object
referenced by the name 'my_func' according to namespace rules.

[1] remember, in Python, functions are objects too.


The second expression has the usual 'function call' semantic.

The first expression allow to write code like:
  my_func_alias = my_func
  my_func_alias()

or
  def my_caller_func(any_func, *args, **kwargs):
print calling %s with *args %s and **kwargs %s \
   % (any_func,
  , .join(args),
  , .join([%s=%s % keyval for keyval in kwargs.items()])

result = any_func(*args, **kwargs)
print result :%s % result
return result

  my_caller_func(my_func)


In fact, '()' is the 'call' operator, that is then applied to the
callable object[2] referenced by 'my_func'. So a function call like

  my_func()

is in fact made in two steps:
- retrieving the object referenced by the name 'my_func'
- trying to apply the '()' call operator on it.


[2] Functions are just one special case of callable object. Lambda are
another, as any instance of a class defining the __call__ method.


the call operator could be implemented like this:
def __call_op__(func_name, *args, **kwargs):
   if hasattr(func_name, __call__):
return func_name.__call__(*args, **kwargs)
   else:
raise TypeError(%s object is not callable % type(func_name))


Ok. Now that you know this, if Python was to support the

  result = my_func arg1, arg2

syntax, how should the expression

  result = my_func

be interpreted ?-)

(hint: remember that the prototype of my_func allow us to call it with
no args at all)

There are good reasons for trying to have a clear and unambigous syntax.
functions-being-objects (as wall as 'other-objects-being-callable) is
one of the strength of Python, and it's a common idiom in Python to pass
functions (or any other callable) around.

BTW, note that there are few languages that doesn't inforce one (and
only one) unambigous syntax for function calls (even VB has a defined
and mandatory syntax for function calls, which is the same as Python's.
What VB has that Python has not is the semantic difference between
functions and procedures, and different syntaxes for both).


HTH
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