Pointers in Python

0 votes

I know Python doesn't have pointers, but is there a way to have this yield 2 instead

>>> a = 1
>>> b = a # modify this line somehow so that b "points to" a
>>> a = 2
>>> b
1

?

Sep 21, 2018 in Python by aryya
• 7,460 points
685 views

1 answer to this question.

0 votes

I want form.data['field'] and form.field.value to always have the same value

This is feasible, because it involves decorated names and indexing -- i.e., completely different constructs from the barenames a and b that you're asking about, and for with your request is utterly impossible. Why ask for something impossible and totally different from the (possible) thing you actually want?!

Maybe you don't realize how drastically different barenames and decorated names are. When you refer to a barename a, you're getting exactly the object a was last bound to in this scope (or an exception if it wasn't bound in this scope) -- this is such a deep and fundamental aspect of Python that it can't possibly be subverted. When you refer to a decorated name x.y, you're asking an object (the object x refers to) to please supply "the y attribute" -- and in response to that request, the object can perform totally arbitrary computations (and indexing is quite similar: it also allows arbitrary computations to be performed in response).

Now, your "actual desiderata" example is mysterious because in each case two levels of indexing or attribute-getting are involved, so the subtlety you crave could be introduced in many ways. What other attributes is form.field suppose to have, for example, besides value? Without that further .value computations, possibilities would include:

class Form(object):
   ...
   def __getattr__(self, name):
       return self.data[name]

and

class Form(object):
   ...
   @property
   def data(self):
       return self.__dict__

The presence of .value suggests picking the first form, plus a kind-of-useless wrapper:

class KouWrap(object):
   def __init__(self, value):
       self.value = value

class Form(object):
   ...
   def __getattr__(self, name):
       return KouWrap(self.data[name])

If assignments such form.field.value = 23 is also supposed to set the entry in form.data, then the wrapper must become more complex indeed, and not all that useless:

class MciWrap(object):
   def __init__(self, data, k):
       self._data = data
       self._k = k
   @property
   def value(self):
       return self._data[self._k]
   @value.setter
   def value(self, v)
       self._data[self._k] = v

class Form(object):
   ...
   def __getattr__(self, name):
       return MciWrap(self.data, name)

The latter example is roughly as close as it gets, in Python, to the sense of "a pointer" as you seem to want -- but it's crucial to understand that such subtleties can ever only work with indexing and/or decorated namesnever with barenames as you originally asked!

answered Sep 21, 2018 by charlie_brown
• 7,720 points

Related Questions In Python

0 votes
2 answers

Do we have pointers in python like other programming languages?

From one point of view, everything is a pointer in Python. Your ...READ MORE

answered Dec 16, 2020 in Python by Gitika
• 65,770 points

edited Jul 8, 2021 by Sarfaraz 62,494 views
+3 votes
7 answers

How can I rename a file in Python?

yes, you can use "os.rename" for that. ...READ MORE

answered Mar 31, 2018 in Python by DareDev
• 6,890 points
20,056 views
+2 votes
2 answers

How can I create a new file in Python?

You can try the below code which ...READ MORE

answered Mar 31, 2018 in Python by anto.trigg4
• 3,440 points
1,326 views
+2 votes
3 answers

what is the practical use of polymorphism in Python?

Polymorphism is the ability to present the ...READ MORE

answered Mar 31, 2018 in Python by anto.trigg4
• 3,440 points
4,914 views
+2 votes
2 answers

Error while printing hello world in python.

You must be trying this command in ...READ MORE

answered Mar 31, 2018 in Python by GandalfDwhite
• 1,320 points
6,451 views
+3 votes
5 answers

How to read multiple data files in python

Firstly we will import pandas to read ...READ MORE

answered Apr 6, 2018 in Python by DeepCoder786
• 1,720 points
15,313 views
+4 votes
6 answers

Use of "continue" in python

The break statement is used to "break" ...READ MORE

answered Jul 16, 2018 in Python by Omkar
• 69,220 points
1,721 views
+5 votes
6 answers

Lowercase in Python

You can simply the built-in function in ...READ MORE

answered Apr 11, 2018 in Python by hemant
• 5,790 points
4,110 views
0 votes
1 answer

Pointers in Python?

I want form.data['field'] and form.field.value to always have the same value This ...READ MORE

answered Aug 20, 2018 in Python by charlie_brown
• 7,720 points
1,109 views
+2 votes
3 answers

How can I play an audio file in the background using Python?

down voteacceptedFor windows: you could use  winsound.SND_ASYNC to play them ...READ MORE

answered Apr 4, 2018 in Python by charlie_brown
• 7,720 points
13,571 views
webinar REGISTER FOR FREE WEBINAR X
REGISTER NOW
webinar_success Thank you for registering Join Edureka Meetup community for 100+ Free Webinars each month JOIN MEETUP GROUP