This code uses a decorator to turn a function into an instance of a special
Pipe class. The Pipe class uses the Python "magic" method __ror__ to
overload the bitwise OR operator (i.e, the | operator). The __or__ magic
method determines the behavior of the | operator when the object with the
method appears on the left of the | operator, and the __ror__ (i.e.,
"reverse" __or__) magic method determines the behavior when the object with
the method appears on the right of the | operator. In this case, the
decorated function is used on the right of the | operator, so the __ror__
method is used. For more details, see
http://minhhh.github.io/posts/a-guide-to-pythons-magic-methods#user-content-numeric-magic-methods.
The Pipe class also includes a __call__ method, so you can call the object
with some arguments, and it returns a new Pipe object, which passes those
arguments to the originally decorated function.
For example, the module defines a concat function:
@Pipe
def concat(iterable, separator=", "):
return separator.join(map(str,iterable))
With the above decorator, concat becomes an instance of the Pipe class,
with self.function set to the function defined above. When you call:
[1, 2, 3] | concat
The __ror__ method of the Pipe object gets called, with the list on the
left passed as the "other" argument.
When you call:
[1, 2, 3] | concat('#')
First, the __call__ method of the Pipe object gets called with "#" as its
argument. It then returns a new Pipe object, and the __ror__ method of that
new Pipe object gets called with the list as the "other" argument.
So, here we've got an example of (a) a decorator implemented as a class
with an __init__ and __call__ method, (b) a Python magic method, and (c)
operator overloading (implemented via the magic method).
Anthony
On Thursday, October 5, 2017 at 4:48:43 PM UTC-4, Ramos wrote:
>
> Reading this
> https://github.com/JulienPalard/Pipe
>
> i tried this simple code
>
>
> import functools
>
>
> class Pipe:
>
> def __init__(self, function):
> self.function = function
> functools.update_wrapper(self, function)
>
> def __ror__(self, other):
> return self.function(other)
>
> def __call__(self, *args, **kwargs):
> return Pipe(lambda x: self.function(x, *args, **kwargs))
> @Pipe
> def list(x):
> return [x]
> @Pipe
> def count(iterable):
> "Count the size of the given iterable, walking thrue it."
> count = 0
> for x in iterable:
> count += 1
> return count
>
>
>
> Can someone tell me why/how this code gives me the | available in the
> console to pipe functions
>
> >> [2,3,4,2,4] | count |list
> [5]
>
>
>
>
>
> Regards
> António
>
>
>
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
> Sem
> vírus. www.avast.com
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
>
> <#CAEM0BxNhzsCkpy=uUdH7xXr6=g3JxtrGvo5M48XZjq55EK=zrw@mail.gmail.com_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>
--
Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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