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Python descriptors to chain methods


Python descriptors to chain methods

By : Ajay Nigam
Date : November 21 2020, 12:01 PM
Does that help If I understand what you're asking, what you want is for the cursor method to return some object with a get method that works as desired. There's no reason the object it returns has to be self; it can instead return an instance of some cursor type.
That instance could have a back-reference to self, or it could get its own copy of whatever internals are needed to be a cursor, or it could be a wrapper around an underlying object from your low-level database library that knows how to be a cursor.
code :
class CRUDCursor(object):
    def __init__(self, c, crud):
        self.crud = crud
        self.cursor = however_you_get_an_actual_sql_cursor(c)

    def get(self, target, where):
        #this is strictly for illustration purposes, I realize all
        #the vulnerabilities this leaves me exposed to.
        query = "SELECT {fields} FROM {table} WHERE {target} = {where}"
        query.format(fields=self.crud.fields, table=self.crud.table, 
                     target=target, where=where)
        self.cursor.execute(query)
        # you may want this to return something as well?

class CRUD(object):
    def __init__(self, table, public_fields):
        self.table = table
        self.public_fields = public_fields

    def fields(self):
        return ', '.join([f for f in self.public_fields])

    # no get method

    def cursor(self, cursor):
        return CRUDCursor(self, cursor)


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Methods don't chain in Python set

Methods don't chain in Python set


By : Greast
Date : March 29 2020, 07:55 AM
I hope this helps . When you do g = f.copy().discard(3), you are storing in g the return value of the method "discard(3)". In this case, it returns nothing, but alters the object. This is why on the second scenario it works.
If all python methods are indeed non-data descriptors can I overwrite a method.__get__?

If all python methods are indeed non-data descriptors can I overwrite a method.__get__?


By : chenchen
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , You can't do this by setting A.m.__get__, because the Python language internals skip the instance dict when looking up special methods like __get__. (This is so, for example, a class Foo that defines a __repr__ method uses type.__repr__ instead of Foo.__repr__ when you do repr(Foo).)
Chain together methods in Python as in Ruby

Chain together methods in Python as in Ruby


By : Tingshuo Xu
Date : March 29 2020, 07:55 AM
wish help you to fix your issue Clarification: The original answer is found below. As commented, the question is on chaining in general, not in any specific case. A clarification on this can be found at the end of this answer.
code :
a = [2,3,1]
b = sorted(a, reverse=True)
a = [2,3,1]
b = a.copy()  # a[:] in python2
b.sort(reverse=True)
foo = they.method.method.method()
foo = my_func(your_func(their_func()))
a = [2,3,1]
b = a.sort()
c = b.reverse()
s = "ab:cd".upper().center(20).partition(':')
print(s)
How can I use descriptors for non-static methods?

How can I use descriptors for non-static methods?


By : user5946140
Date : March 29 2020, 07:55 AM
I wish this help you Considering method(param) returns a descriptor, you may invoke it manually with a property like so:
code :
class SomeClass(object):

    def __init__(self):
        self._descriptor = method(param)

    @property
    def my_attribute(self):
        return self._descriptor.__get__(self, self.__class__)

    @my_attribute.setter
    def my_attribute(self, value):
        self._descriptor.__set__(self, value)
Prototype chain using Object.assign and descriptors

Prototype chain using Object.assign and descriptors


By : adxl345arduino
Date : March 29 2020, 07:55 AM
like below fixes the issue Because the first argument to Object.assign is the object to assign to. Then Object.assign returns a reference to that object. It assigns from subsequent arguments, but you aren't supplying any. So the end result is that firstObject and secondObject just point to the same object:
code :
var firstObject = {
  set a(val) {
  	this._a_ = val;
  },
  get a() {
  	return this._a_;
  }
}

var secondObject = Object.assign(firstObject);
console.log("Same object? " + (firstObject === secondObject));
var secondObject = Object.assign({}, firstObject);
// Note -------------------------^^^^
var firstObject = {
  set a(val) {
  	this._a_ = val;
  },
  get a() {
  	return this._a_;
  }
}

var secondObject = Object.assign({}, firstObject);

secondObject.a = 3;

console.log(secondObject.a); // 3
console.log(firstObject.a);  // undefined

firstObject.a = 42;
console.log(firstObject.a);  // 42
console.log(secondObject.a); // still 3

console.log(
  "firstObject's a descriptor:",
  Object.getOwnPropertyDescriptor(firstObject, "a")
);
console.log(
  "secondObject's a descriptor:",
  Object.getOwnPropertyDescriptor(secondObject, "a")
);
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