Re: Why python doesn't use syntax like function(, , x) for default parameters?
Op 2006-03-10, Terry Reedy schreef [EMAIL PROTECTED]: Antoon Pardon [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] but nobody seems to have a problem with range(n) where n suddenly is the second parameter and we use the default for the first. Actually, I consider the unique calling pattern for x/range to be something of a wart. Learning this inconsistency was at least a minor problem. It is a rather extreme example of typing laziness beats purity. Well then we can at least agree on that. Given that enumerate() eliminate many uses of range(), it might be worth considering requiring the start param. range(0,n) only takes two more keystrokes. Better maybe to shorten range to rng to get them back ;-) I can't use enumerate that much. I usually work with a Table which is like a list, but the index can start at any integer value. Enumerate doesn't work well with a table. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Op 2006-03-10, Terry Reedy schreef [EMAIL PROTECTED]: Antoon Pardon [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] but nobody seems to have a problem with range(n) where n suddenly is the second parameter and we use the default for the first. Actually, I consider the unique calling pattern for x/range to be something of a wart. Learning this inconsistency was at least a minor problem. It is a rather extreme example of typing laziness beats purity. Given that enumerate() eliminate many uses of range(), it might be worth considering requiring the start param. range(0,n) only takes two more keystrokes. Better maybe to shorten range to rng to get them back ;-) Take the split method of strings. Personnaly I would prefer to be able to write: s.split(,3) Instead of having to write s.split(None,3) The reason is that None is IMO an implemenation detail here. Also the alternative s,split(maxsplit=3) doesn't work in this case. What may be an option for the future is a Default Object. So that if you have. def f(x=0,y=0): ... then f(Default, 5) would be equivallent to f(0,5) -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Op 2006-03-10, Diez B. Roggisch schreef [EMAIL PROTECTED]: Those default values are not 0 and size-of-sequence, you may have only experience with situations where they behave as such but that is not the same. Well, it might be - but the conceptual behavior is (usually) the same. If you need to know these values then you will need to know them just as much when a keyword is used or when the default values are used later. Calling f(3) or f(arg5=3) Will give you no more a clue about the missing default values than calling f(,3) At least in the last call you are given a clue about missing arguments. I didn't argue against that - I don't like the proposal, but I'm pretty sure that it won't be accepted in any way whatsoever so I don't bother. You argued that f(,,3) would somehow be hard to figure out. I just wanted to point out that you proclaim false evidence for a similar situation already being part of python, and that thus the f(,,1) syntax was justified. I didn't claim that the f(,,1) syntax was justified. I asked for an explanation about why something like f(,,3) would be hard to figure out. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Why python doesn't use syntax like function(, , x) for default parameters?
I mean, it's very convenient when default parameters can be in any position, like def a_func(x = 2, y = 1, z): ... (that defaults must go last is really a C++ quirk which is needed for overload resolution, isn't it?) and when calling, just omit parameter when you want to use defaults: a_func(, , 3) There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Is there some contradiction in python syntax which disallows an easy implementation of this feature, or just nobody bothered with this? If former is the case, please show me why, because I badly need this feature in embedded python app (for compatibility with other language that uses such syntax) and might venture to implement it myself, so don't want to waste time if it's gonna break something. Or maybe it might be an idea for enhancement proposal? -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Dmitry Anikin wrote: Is there some contradiction in python syntax which disallows an easy implementation of this feature, or just nobody bothered with this? If former is the case, please show me why, because I badly need this feature in embedded python app (for compatibility with other language that uses such syntax) and might venture to implement it myself, so don't want to waste time if it's gonna break something. I think you would find it hard to implement exactly that in Python. Of course what you can do easily enough is invent a magic 'missing' value and map Python calls of: a_func(missing, missing, 3) to a call of: a_func(,,3) in your other language. It seems to me though that writing: a_func(z=3) ought to be clearer to anyone reading the code, especially when you come back to your code in 6 months time and find: b_func(,,,12) Remember Python is a dynamic language, so the compiler cannot tell which function you are actually calling. In a statically bound language parameter defaults are often restricted to constant values and the default values are simply inserted in place of any missing arguments when the call is compiled. That isn't possible in Python, so the interpreter has to insert the missing values when you actually make the call. The code to do that is complex enough with the current restrictions. To allow arbitrary arguments to be defaulted, I think you would have to add a new magic value to represent a missing parameter, make the compiler pass that in place of any omitted positional parameters, and then make the function call code check all parameters to see if they are missing values and if so substitute the actual default. It would be possible, but it doesn't really give you any additional power since you can already do that in the cases where you need it by using keyword arguments or by passing an explicit value to mean 'replace this parameter by some other canned value'. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
On 10 Mar 2006 09:51:01 GMT Duncan Booth [EMAIL PROTECTED] wrote: Dmitry Anikin wrote: Is there some contradiction in python syntax which disallows an easy implementation of this feature, or just nobody bothered with this? If former is the case, please show me why, because I badly need this feature in embedded python app (for compatibility with other language that uses such syntax) and might venture to implement it myself, so don't want to waste time if it's gonna break something. I think you would find it hard to implement exactly that in Python. Of course what you can do easily enough is invent a magic 'missing' value and map Python calls of: a_func(missing, missing, 3) to a call of: a_func(,,3) It's not uncommon, of course, to use None for this purpose. I have a lot of code that does something like: def myfunc(a, b, c): if a is None: a = [] ... -- Terry Hancock ([EMAIL PROTECTED]) Anansi Spaceworks http://www.AnansiSpaceworks.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Dmitry Anikin [EMAIL PROTECTED] wrote: There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. I badly need this feature in embedded python app (for compatibility with other language that uses such syntax) Can you tell us more about what it is that you're trying to do? Or maybe it might be an idea for enhancement proposal? You can always write up a PEP, but to be honest, this doesn't sound like one that would meet with much enthusiasm from the community. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Dmitry Anikin wrote: I mean, it's very convenient when default parameters can be in any position, like def a_func(x = 2, y = 1, z): ... (that defaults must go last is really a C++ quirk which is needed for overload resolution, isn't it?) I've no idea why C++ required defaults last; it certainly seems wise to avoid confusion with the positionals in Python. and when calling, just omit parameter when you want to use defaults: a_func(, , 3) Yerch! So now you've forced all arguments to be positional? This doesn't seem like an improvement. And it's just plain fugly. There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Whereas you can invariably remember their positions? I don't think so. Is there some contradiction in python syntax which disallows an easy implementation of this feature, or just nobody bothered with this? If former is the case, please show me why, because I badly need this feature in embedded python app (for compatibility with other language that uses such syntax) and might venture to implement it myself, so don't want to waste time if it's gonna break something. Or maybe it might be an idea for enhancement proposal? The thing about enhancement proposals is that they are supposed to *improve* the language. Frankly I wouldn't see this as any kind of enhancement. If you have a large program to translate from another language you will probably find that a modest application of Python suffices to translate all the calls into whatever form turns out to be required in Python. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd www.holdenweb.com Love me, love my blog holdenweb.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Op 2006-03-10, Roy Smith schreef [EMAIL PROTECTED]: Dmitry Anikin [EMAIL PROTECTED] wrote: There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. Could you explain what is so hard in figuring out: func(,,4) We sure don't seem to have a problem with figuring out things like lst[::2] Personnaly in a situation where it is likely that the first parameter is going to take a default and the second parameter is going to vary a lot, I would have prefered that to be visible in how the function is called, instead of a call with only one argument being interpreted as being the value for the second parameter. More specifically I would have preferred the possibility of range(,n) and this being equivallent to range(0,n) instead of range(n) being equivallent to range(0,n). -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Antoon Pardon wrote: Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. Could you explain what is so hard in figuring out: func(,,4) We sure don't seem to have a problem with figuring out things like lst[::2] That is the usual polemics. Its a HUGE difference if I'm supposed to remember 2 default values that are 0 and size-of-sequence, in a specialized syntax, than arbitrary values f(,3) in some arbitrary function. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
In article [EMAIL PROTECTED], Antoon Pardon [EMAIL PROTECTED] wrote: Op 2006-03-10, Roy Smith schreef [EMAIL PROTECTED]: Dmitry Anikin [EMAIL PROTECTED] wrote: There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. Could you explain what is so hard in figuring out: func(,,4) Because while I probably remember what func does (especially if it's well named), it's less likely that I remember all the arguments it takes, and even less that I remember what order they come in. Let's say I've got a function which makes a network connection. It takes optional arguments for a port number to connect to, a timeout (in seconds) and a buffer size (in kbytes) to use. If we used your syntax, what does connect (,,20) mean? You have to go look up the definition of the function to find out, don't you? But, if I wrote connect (port=20), it's obvious to anybody reading the code what the 20 is. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(,,x) for default parameters?
Antoon Pardon wrote: Op 2006-03-10, Roy Smith schreef [EMAIL PROTECTED]: Dmitry Anikin [EMAIL PROTECTED] wrote: There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. Could you explain what is so hard in figuring out: func(,,4) Your func has only three parameters, and only one non-default. I think all have reasonable defaults, I want to provide several means you might end up with bugs like this. func(,,,1.2e-3,7.6e18,3.124576,3567.0,) func(,,1.24e3,1,21.26e4,,,1220,57,35,0) # bug TypeError: func() takes exactly 8 arguments (9 given) Now what are the correct arguments? 1220.57, 35,and 0 1220,57.35, and 0 1220,57,and 35.0 With keywords parameters, this is easy to answer. func(y=1.2e-3, z=7.6e18, i=3.124576, j=3567.0) func(x=1.24e3, y=1, z=21.26e4, j=1220, k=57,35, w=0) # bug SyntaxError: non-keyword arg after keyword arg. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Op 2006-03-10, Diez B. Roggisch schreef [EMAIL PROTECTED]: Antoon Pardon wrote: Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. Could you explain what is so hard in figuring out: func(,,4) We sure don't seem to have a problem with figuring out things like lst[::2] That is the usual polemics. Its a HUGE difference if I'm supposed to remember 2 default values that are 0 and size-of-sequence, in a specialized syntax, Those default values are not 0 and size-of-sequence, you may have only experience with situations where they behave as such but that is not the same. than arbitrary values f(,3) in some arbitrary function. If you need to know these values then you will need to know them just as much when a keyword is used or when the default values are used later. Calling f(3) or f(arg5=3) Will give you no more a clue about the missing default values than calling f(,3) At least in the last call you are given a clue about missing arguments. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Op 2006-03-10, Roy Smith schreef [EMAIL PROTECTED]: In article [EMAIL PROTECTED], Antoon Pardon [EMAIL PROTECTED] wrote: Op 2006-03-10, Roy Smith schreef [EMAIL PROTECTED]: Dmitry Anikin [EMAIL PROTECTED] wrote: There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. Specifying the names of the keyword parameters costs you a little typing once, but saves everybody (including yourself) a lot of grief later when you're trying to figure out what the heck your code does 6 months later. Could you explain what is so hard in figuring out: func(,,4) Because while I probably remember what func does (especially if it's well named), it's less likely that I remember all the arguments it takes, and even less that I remember what order they come in. Do you have trouble remembering that range(n) is actually providing the second parameter to the function and what it does? Let's say I've got a function which makes a network connection. It takes optional arguments for a port number to connect to, a timeout (in seconds) and a buffer size (in kbytes) to use. If we used your syntax, what does connect (,,20) mean? You have to go look up the definition of the function to find out, don't you? But, if I wrote connect (port=20), it's obvious to anybody reading the code what the 20 is. I don't consider this an argument. We already have the problem that we need to figure out what connect(20) means. connect(,,20) will at least make it clear that some parameters are missing. My syntax doesn't make it easier to introduce inclarities than python can. Sure connect(port=20) provides extra clarity, but nobody seems to have a problem with range(n) where n suddenly is the second parameter and we use the default for the first. If we want to allow things like that I would prefer range(,n) that at least makes it clear what is going on. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Those default values are not 0 and size-of-sequence, you may have only experience with situations where they behave as such but that is not the same. Well, it might be - but the conceptual behavior is (usually) the same. If you need to know these values then you will need to know them just as much when a keyword is used or when the default values are used later. Calling f(3) or f(arg5=3) Will give you no more a clue about the missing default values than calling f(,3) At least in the last call you are given a clue about missing arguments. I didn't argue against that - I don't like the proposal, but I'm pretty sure that it won't be accepted in any way whatsoever so I don't bother. I just wanted to point out that you proclaim false evidence for a similar situation already being part of python, and that thus the f(,,1) syntax was justified. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Antoon Pardon [EMAIL PROTECTED] wrote: Do you have trouble remembering that range(n) is actually providing the second parameter to the function and what it does? Yes. I don't use range() everyday, and it's very rare that I use more than one argument. I do remember that there are additional (optional) arguments to range which alter the sequence (start point and step), but I certainly don't remember which is which. If I needed to use it, I would go look it up. On the other hand, if I saw range (10, step=2) written, it would be immediately obvious what was going on without need to refer to the docs. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Antoon Pardon [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] but nobody seems to have a problem with range(n) where n suddenly is the second parameter and we use the default for the first. Actually, I consider the unique calling pattern for x/range to be something of a wart. Learning this inconsistency was at least a minor problem. It is a rather extreme example of typing laziness beats purity. Given that enumerate() eliminate many uses of range(), it might be worth considering requiring the start param. range(0,n) only takes two more keystrokes. Better maybe to shorten range to rng to get them back ;-) Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Some example (from real life).
def ChooseItems(StartDate, EndDate, Filter):
#function returns a set of some items in chronological order
#from required interval possibly using filter
ChooseItems() #get everything
ChooseItems('01.01.2000', ,SomeFilter) #get everything after a date using filter
ChooseItems(, '01.01.2000') #get everything before a date
ChooseItems(, , SomeFilter) #get everything using filter
Now compare this to something which (I hope) is rather pythonian
Seq[:] #get everything
Seq[2::3] #get everything after an index using filter (filter every third value)
Seq[:3] #get everythin before an index
Seq[::4] #get everything using a filter
Do you see any significant difference?
I understand that many do not need such a syntax, I don't understand
why someone would be AGAINST it. I don't propose to CHANGE anything
in python (right now this syntax is error anyway). What I propose is just
ADD another way of calling a function with keyword parameters but using
POSITIONS instead of NAMES. And sometimes position is easier to
remember than name. Anyway, who wants names let them use names.
Who wants positions let them use positions. But to have a CHOICE is
always good. As far as the choice itself doesn't damage anything,
and I don't think that my does.
I think that if we compare
ChooseItems('01.01.2000', ,SomeFilter)
and
ChooseItems(StartDate='01.01.2000', Filter=SomeFilter)
the first one is more readable, 'cos you see
what is meant right away. In second one you have to
actually READ the keyword names to understand.
It's not the common case, of course, but still, why
not have a choice to use it?
Some other examples which might benefit
SetDate(year, month, day)
SetDate(, month+1) # set next month, leaving year and day
SetDate(, , 31) # set to end of month, not changing year
#(wrong date adjusted automatically, of course)
FormatFloat(Float, Length, Precision, FormatFlags)
You might want precision, leaving length default, or just use FormatFlags
In fact, I became so used to convenience of such syntax that
it was a disappointment not to find it in python.
Please, don't try to scare me with 25-parameter functions.
This is not for them. But to remember positions of two to
five parameters is actually easier (if their order has some
logic) then what are their names: startDate ? beginDate?
firstDate? openDate? Date1?
The same approach can be used with tuples:
(, , z) = func() # returning three element tuple()
You think
z = func()[2]
is actually more clear? - By the way, I want THIRD value,
not SECOND. And tuples don't have keyword names, do they?
And what about
(a, , b) = func()
...well, maybe I got carried away a little...
Finally, if syntax
func (None, None, 10)
seems natural to you, I propose to make it even more
natural: I don't want some None passed as argument,
I don't want anything at all passed, so I just use empty space
func ( , , 10)
And the called func don't have to bother with checking
None for EACH argument but will happily use defaults instead.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
Some example (from real life).
def ChooseItems(StartDate, EndDate, Filter):
#function returns a set of some items in chronological order
#from required interval possibly using filter
ChooseItems() #get everything
ChooseItems('01.01.2000', ,SomeFilter) #get everything after a date using filter
ChooseItems(, '01.01.2000') #get everything before a date
ChooseItems(, , SomeFilter) #get everything using filter
Now compare this to something which (I hope) is rather pythonian
Seq[:] #get everything
Seq[2::3] #get everything after an index using filter (filter every third value)
Seq[:3] #get everythin before an index
Seq[::4] #get everything using a filter
Do you see any significant difference?
I understand that many do not need such a syntax, I don't understand
why someone would be AGAINST it. I don't propose to CHANGE anything
in python (right now this syntax is error anyway). What I propose is just
ADD another way of calling a function with keyword parameters but using
POSITIONS instead of NAMES. And sometimes position is easier to
remember than name. Anyway, who wants names let them use names.
Who wants positions let them use positions. But to have a CHOICE is
always good. As far as the choice itself doesn't damage anything,
and I don't think that my does.
I think that if we compare
ChooseItems('01.01.2000', ,SomeFilter)
and
ChooseItems(StartDate='01.01.2000', Filter=SomeFilter)
the first one is more readable, 'cos you see
what is meant right away. In second one you have to
actually READ the keyword names to understand.
It's not the common case, of course, but still, why
not have a choice to use it?
Some other examples which might benefit
SetDate(year, month, day)
SetDate(, month+1) # set next month, leaving year and day
SetDate(, , 31) # set to end of month, not changing year
#(wrong date adjusted automatically, of course)
FormatFloat(Float, Length, Precision, FormatFlags)
You might want precision, leaving length default, or just use FormatFlags
In fact, I became so used to convenience of such syntax that
it was a disappointment not to find it in python.
Please, don't try to scare me with 25-parameter functions.
This is not for them. But to remember positions of two to
five parameters is actually easier (if their order has some
logic) then what are their names: startDate ? beginDate?
firstDate? openDate? Date1?
The same approach can be used with tuples:
(, , z) = func() # returning three element tuple()
You think
z = func()[2]
is actually more clear? - By the way, I want THIRD value,
not SECOND. And tuples don't have keyword names, do they?
And what about
(a, , b) = func()
...well, maybe I got carried away a little...
Finally, if syntax
func (None, None, 10)
seems natural to you, I propose to make it even more
natural: I don't want some None passed as argument,
I don't want anything at all passed, so I just use empty space
func ( , , 10)
And the called func don't have to bother with checking
None for EACH argument but will happily use defaults instead.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(,,x) for default parameters?
Dmitry Anikin napisał(a):
Some example (from real life).
def ChooseItems(StartDate, EndDate, Filter):
#function returns a set of some items in chronological order
#from required interval possibly using filter
ChooseItems() #get everything
ChooseItems('01.01.2000', ,SomeFilter) #get everything after a date
using filter
ChooseItems(, '01.01.2000') #get everything before a date
ChooseItems(, , SomeFilter) #get everything using filter
Now compare this to something which (I hope) is rather pythonian
Seq[:] #get everything
Seq[2::3] #get everything after an index using filter (filter every
third value)
Seq[:3] #get everythin before an index
Seq[::4] #get everything using a filter
Do you see any significant difference?
You're not comparing what you should. Range has only 3 parameters and is
a standard part of a language. Even if it's not obvious for someone
which parameters mean what in different combinations, it's not that hard
to look up in a manual. But user-defined functions are allowed to have
any number of arguments, with any possible meaning. That means it's
impossible to learn to recognize arguments exclusively by position
(which can be done for range), you have to look up function definition
*each time*.
And please remember that when writing a function, you define defaults as
values that user will mostly consider as appropriate. So if he doesn't
define them, that means he doesn't care. And Python syntax shows exactly
this intention. Your proposed syntax doesn't, as it suggest something
that user should know about is going on.
Now look at your example rewritten with standard Python keyword syntax.
If you know nothing about ChooseItems function, which version in your
opinion is more informative?
# get everything
ChooseItems()
# get everything after a date using filter
ChooseItems(after='01.01.2000', filter_with=SomeFilter)
# get everything before a date
ChooseItems(before='01.01.2000')
# get everything using filter
ChooseItems(filter_with=SomeFilter)
I understand that many do not need such a syntax, I don't understand
why someone would be AGAINST it. I don't propose to CHANGE anything
in python (right now this syntax is error anyway). What I propose is just
ADD another way of calling a function with keyword parameters but using
POSITIONS instead of NAMES. And sometimes position is easier to
remember than name. Anyway, who wants names let them use names.
Who wants positions let them use positions. But to have a CHOICE is
always good. As far as the choice itself doesn't damage anything,
and I don't think that my does.
With this attitude Python will end up being Perl. Current semantics of
calling functions are already good enough to write clean and
understandable code.
I think that if we compare
ChooseItems('01.01.2000', ,SomeFilter)
and
ChooseItems(StartDate='01.01.2000', Filter=SomeFilter)
the first one is more readable, 'cos you see
what is meant right away. In second one you have to
actually READ the keyword names to understand.
It's not the common case, of course, but still, why
not have a choice to use it?
I still think reading is better than guessing. :) Choosing good names
for arguments is another important factor (as shown in last example) in
readability.
Some other examples which might benefit
SetDate(year, month, day)
SetDate(, month+1) # set next month, leaving year and day
SetDate(, , 31) # set to end of month, not changing year
#(wrong date adjusted automatically, of course)
In Poland we usually write dates in day-month-year notation. Having
function calls like this:
SetDate(year=y, month=m, day=d)
SetDate(month=m+1)
SetDate(day=31)
will be understandable by anyone.
Please, don't try to scare me with 25-parameter functions.
This is not for them. But to remember positions of two to
five parameters is actually easier (if their order has some
logic) then what are their names: startDate ? beginDate?
firstDate? openDate? Date1?
I must disagree. If you choose argument names wisely you won't have any
trouble remembering which is which.
The same approach can be used with tuples:
(, , z) = func() # returning three element tuple()
You think
z = func()[2]
is actually more clear? - By the way, I want THIRD value,
not SECOND. And tuples don't have keyword names, do they?
It's not cleaner. It's error-prone, as you may lost one comma somewhere.
You also have to literally count what is the index of returned tuple
value that will be binded to z.
Finally, if syntax
func (None, None, 10)
seems natural to you, I propose to make it even more
natural: I don't want some None passed as argument,
I don't want anything at all passed, so I just use empty space
func ( , , 10)
And the called func don't have to bother with checking
None for EACH argument but will happily use defaults instead.
If you would write it as func(third=10) it would be clearer that
func(, , 10) and called function will still behave as you expect
(without checking for
Re: Why python doesn't use syntax like function(, , x) for default parameters?
On Fri, 10 Mar 2006 12:06:57 +0300, Dmitry Anikin wrote: I mean, it's very convenient when default parameters can be in any position, like def a_func(x = 2, y = 1, z): ... (that defaults must go last is really a C++ quirk which is needed for overload resolution, isn't it?) I'm confused... it looks to me like the defaults are *first*, not last, in the above definition. We write from left to write in English, so normal convention in English is that first - last, not last - first. and when calling, just omit parameter when you want to use defaults: a_func(, , 3) Can you do this? another_func(,,,4) That looks like bug-city to me. (Did I mean 4 to go in the fourth position or fifth?) In any case, given the way Python defaults work, the commas are superfluous. There is no ambiguity: def f(w, x, y=1, z=1): pass Positional arguments without defaults *must* go first, and must be supplied: f(5, 6) = w=5, x=6, y=1, z=1 Commas would be pointless: f(5, 6, , ) isn't needed, because the first and second arguments are already assigned to the w and x arguments before the first empty comma is spotted. You can't do this: f(, , 5, 6) = w,x = default, y=5, z=6 because w and x don't have defaults. There are often situations when a function has independent parameters, all having reasonable defaults, and I want to provide just several of them. In fact, I can do it using keyword parameters, but it's rather long and you have to remember/lookup names of parameters. And you think it is easier to remember the position of parameters rather than their names? -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why python doesn't use syntax like function(, , x) for default parameters?
On Fri, 10 Mar 2006 11:33:56 -0500, Terry Reedy wrote: Actually, I consider the unique calling pattern for x/range to be something of a wart. Learning this inconsistency was at least a minor problem. It is a rather extreme example of typing laziness beats purity. Amazing. I consider it to be a rather extreme example of practicality beating purity, an excellent example of interface design. But I guess that's why Guido is BDFL. Well, that and the fact that he invented Python *wink* -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
