[Python-ideas] "Immutable Builder" Pattern and Operator

[Serhiy Storchaka]

On 23.01.17 01:30, Soni L. wrote:
> On 22/01/17 08:54 PM, Serhiy Storchaka wrote:
>> On 23.01.17 00:45, Soni L. wrote:
>>> I've been thinking of an Immutable Builder pattern and an operator to go
>>> with it. Since the builder would be immutable, this wouldn't work:
>>>
>>> long_name = mkbuilder()
>>> long_name.seta(a)
>>> long_name.setb(b)
>>> y = long_name.build()
>>
>> I think the more pythonic way is:
>>
>> y = build(a=a, b=b)
>>
>> A Builder pattern is less used in Python due to the support of keyword
>> arguments.
>
> I guess you could do something like this, for an IRC bot builder:
>
> fnircbotbuilder = mkircbotbuilder(network="irc.freenode.net", port=6697,
> ssl=true)
> mainbot = mkircbotbuilder(parent=fnircbotbuilder,  # ???
>                           channels=["#bots"]).build()
> fndccbotbuilder = mkircbotbuilder(parent=fnircbotbuilder, dcc=true,
> channeldcc=true)
> dccbot = mkircbotbuilder(parent=fndccbotbuilder,
> channels=["#ctcp-s"]).build()
> otherircbotbuilder = mkircbotbuilder(parent=fndccbotbuilder,
> network="irc.subluminal.net")  # because we want this whole network
> otherbot = mkircbotbuilder(parent=otherircbotbuilder,
> channels=["#programming"]).build()    # to use DCC and channel DCC
>
> But this would be cleaner:
>
> botbuilder =
> mkircbotbuilder().network("irc.freenode.net").port(6697).ssl(true)
> mainbot = botbuilder.channels(["#bots"]).build()
> botbuilder .= dcc(true).channeldcc(true)
> dccbot = botbuilder.channels(["#ctcp-s"]).build()
> botbuilder .= network("irc.subluminal.net")
> otherbot = botbuilder.channels(["#programming"]).build()

In Python you can save common options in a dict and pass them as 
var-keyword argument. Or use functools.partial. In any case you don't 
need a builder class with the build method and a number of configuring 
methods. It can be just a function with optional keyword parameters.

A Builder pattern is often used in languages that don't support passing 
arguments by keyword and partial functions. Python rarely needs the 
purposed class implementing a Builder pattern. Actually a Builder 
pattern is built-in in the language as a part of syntax.