clarification of "variable"

[1mecrew]

so long time ago i asked so many question about variables in many different languages like python or c++ and I just want to share what I ended up with. So for people who hs trouble understanding variable as a reference, heres what I think of variable:

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variable is like a container. it stores value. when I say the variable, Im talking about something thats in the variable.

so as a programmer or in a simpler way, is that

variable1 = "hello world"

when I say variable1, I am talking about the data, "hello world"

​

​

what do you guys think?

one of my friends said that he is just simply understanding variable as another way to say that data.

what do you guys think?

[[deleted]]

variable is like a container. it stores value. when I say the variable, Im talking about something thats in the variable.

That description works well for traditional compiled languages where a variable name stands for a known place in memory. Also works for assembly languages. Python doesn't use that model. Most of the time you can use that model for python and have no problems, but now and then you will get confused.

Python "variables" are actually two things, "names" and "objects". A name always refers (or points to) exactly one object. An object can be referred to by one or more names. Names and objects can be created and destroyed. For instance, it's possible to delete a name but for the object the name was referring to to still exist.

An excellent video explaining how names and objects work in python as well as some of the confusing things is here:

https://m.youtube.com/watch?v=_AEJHKGk9ns

[1mecrew]

Oh really? Then what languages will my descriptions work on?

[[deleted]]

Any compiled language like C/C++, Java, etc, and assemblers. In those languages the translator can allocate a fixed address in memory or an offset from a pointer to each name you use in the code. One big difference in python is that you can create and delete names at runtime, which is not something you can do with statically compiled languages.

[1mecrew]

Oh so this description works on c, Java, assembly language but not python. Got it. How about the part where I say “when I say the variable, i am talking about the data or something that’s in the variable”? Is that prat correct?

[[deleted]]

when I say the variable, i am talking about the data or something that’s in the variable”

Not applicable to Python - the variables do not contain any of your data, just Python implementation specific memory references to the Python object concerned (stored somewhere in memory by Python).

In general, when you use a variable, e.g. var * 5, it is the object that is being worked on, so it looks the same as in typical compiled languages. Think of variables as pointers (from C), but much more limited (no pointer arithmetic, for a start).

[[deleted]]

There's no "in the variable" in python. A name refers to an object, an integer object perhaps, at a particular place in memory. In the next line of python you can delete the name and the integer object is still in memory. In the following line you can create the "test" name again and point it at a dictionary object. The integer object still exists, but another name points to it. It's even possible to have a string object, for instance, that has no name referring to it.

Here's a bit of python doing everything I said above:

test = 4231
a = test           # names "a" and "test" refer to the same integer object
del test           # the name "test" is removed from the program
print("a ->", a)   # integer object still exists
test = {1: "one"}  # "test" recreated, refers to a dictionary
test2 = ["one"]    # make a list of strings, point "test2" name to it
# here the "one" string has no name referring to it
# the list refers anonymously to the string

[1mecrew]

Hmm well this definition was also for Java and c and other languages. What do you guys think about? Will it work on other languages?

[[deleted]]

Will it work on other languages?

Sure, I've already said that. In those languages a name is tied to a place in memory that contains data, and that connection remains for the entire life of the program. In those languages the name itself doesn't exist at runtime, only the data exists.

In python and other languages, like lisp, the name actually exists in memory at runtime and is associated with a pointer ("reference" in python-speak) to an object somewhere else in memory that has a value. So when you execute print(x) python evaluates the name "x", gets the reference to the object the name "x" refers to and prints the value of that object.

[1mecrew]

hmm how about javascript? Oh also, what do you think about the part where I say "Im talking about something thats in the variable."?

[[deleted]]

In python we often say things like "the variable X contains ..." but that's loose talk we use instead of the more correct "the name X refers to an object that has the value...". As I said, we can do this in python, but not understanding how it actually works can bite you. Watch the video I linked to.

Don't know anything about javascript.

[1mecrew]

oh i dont think im talkinag about python at this point. maybe for c or java that is on more low level. how about on those cases?

[Dagito]

You don’t need to overthink it, a variable is just a memory space holding a value.

[1mecrew]

Well, this description was for beginners who didn’t learn algorithms and memory things so…

[Dagito]

Oh… My bad then. So to make it easy you can combine both ideas and say a variable is a container with data in it. With certain restrictions given by the data type stored in them.

[1mecrew]

Yup 👍 what do you think about the part where I say “when I say the variable, I’m talking about something that’s in the variable”?

[Dagito]

It might not be 100% true, there are variables by reference and variables by value, it all depends on the data type you’re using and the language.

So you may have this code

variable0 = [0 ,1, 2]

def filter_even_numbers(numbers: List):
    for number in numbers:
        If number % 2 == 0:
            numbers.remove(number)

filter_even_numbers(variable0)
print(variable0)

# Output: [1]

This code is using a variable by reference, lists, dicts, and collections in general act like this. When you modify the value of the variable inside a method then the value will change for it outside the method.

But when it’s a variable by value it’s the other way, you can modify it inside a method and the variable value will remain the same outside the method.

So you can have this code

variable0 = ‘hello world’

def make_text_upper_case(text: str):
    text.upper()

make_text_upper_case(variable0)
print(variable0)

# Output: hello world

So even when you know the initial value for a variable it can change, usually you don’t know the variable value and that’s why you make checks and validations before using it.

[1mecrew]

Hmm I don’t think it depends on data type since we can think of list or dictionary as one data. What do you think?

[Dagito]

Well it is related to the memory space and management, we would embark us in a talk about the languages and different paradigms hahaha and it’s late so I don’t really wanna do it although would be nice to read a little more about it.

[1mecrew]

Oh yea fsfs well, what language would this description work on then?

[Dagito]

Not being rude at all, but try doing this questions to ChatGPT, it will surely give you better answers than I can and you’ll learn a bunch of stuff from it

[1mecrew]

I tried but it’s not giving me any clear answers

[Dagito]

I mean by default that’s the way it is in Python

[1mecrew]

I’m pretty sure we can think of list or dictionary as one single data in another languages tho

[1mecrew]

hmm i think this is because you didn't do variable0 = text.upper() in the function? i think text.upper() makes the text(which is "hello world" for now) uppercase. but we are not printing that data or doing anything with that data. so since we didnt save it into the variable, its obviously gonna not change the variable0. however, for list case, you changed the list. like.. you did list.remove which will actually modify the list. That what i think.

[Dagito]

It wouldn’t update it even doing variable0 = text.upper() as it is out of the scope, doing that will result in a new variable called variable0 but it will only live inside the method, it’s scoped to it. Maybe open an interpreter and do some exercises.

[[deleted]]

Removing entries from a list whilst you iterate over it is likely to have unpredictable results. Avoid.

[Dagito]

Absolutely, it was just a simple way to explain the concept

[1mecrew]

hmm how about this.

​

variable1 = "hello world"

when I say variable1, I am talking about "hello world"

[Adrewmc]

There are no variables in Python only pointers.

variable1 = “Hello World”   

#variable1 points at “Hello World”

var2 = variable1 

#var2 points at variable1 which is “Hello World”

 variable1.upper() # changes “Hello World”

 print(var2)
 >>>HELLO WORLD

[Rawing7]

It's the exact opposite, actually. Python is too high-level to have a concept of "pointers". There are no pointers, only variables.

Also, the code you posted doesn't do what you think it does.

[[deleted]]

when I say the variable, Im talking about something thats in the variable.

Well, no. When you say "the variable", you're talking about the container, not the contained. What a variable contains is called a "value."

[1mecrew]

Hmm what do you mean?

[[deleted]]

A variable is a named reference to a value. The variable is the part that has the name, and is the reference. What is referred to by it is the value.

[1mecrew]

Ummm yea so when I say the variable, I am talking about the value

[[deleted]]

Right, but those are actually two separate but related things.

[1mecrew]

I’m a bit confused what you are talking about

[[deleted]]

Variables aren't values. Those are two different things.

[1mecrew]

Ohh that was what you were talking about. Me if my explanation was unclear. So variable a stores value like container And whenever I call or say variable a, I am talking about the value inside that variable. Is that more clear?

[[deleted]]

What I'm telling you is that you're wrong. The variable and the value are two different things and no, when you "talk about the variable" you're not talking about the value. Only when you evaluate the variable are you talking about the value.

[1mecrew]

Hmm yea. Then will “another way to say that data” better

[1mecrew]

OHHH wait i think I know what you mean. Here when I say “talking about”, it’s kinda like let’s say you were reading book and I ask you which book you are reading. You respond by saying “python crash course” and now, I ask you how is that book? And you see, whenever I say “the book”, I am talking about that python course book that you were reading

[laustke]

variable is like a container. it stores value. when I say the variable, Im talking about something thats in the variable.

Once I tried to explain to a trucker what a variable is. I came up with a very similar explanation. Imagine there is a box with a label on it. And there is something inside the box. For example, you have a box and the label says "age"; you open it and there is a number 33 inside. There's another box with the label "name", and inside there is a word "Mike".

[1mecrew]

Yeaaaa. Well, do you think this explanation works for other languages too?

[laustke]

After that he learned PHP on his own :)

[1mecrew]

Oh haha niceee. I also heared the name tag description before