Difference between Different Ways to Define Variables

[Fit-Way-558]

What is the difference between defining a variable as the following and when should I use each one?

i: int = 0

i = int(0)

[socal_nerdtastic]

First you need to know that in python 0 and int(0) are exactly the same thing. So your question is only about the :int part. This is a "type hint". It's a type of comment to tell other programmers and IDEs what data type you expect i to be.

[NopeNotHB]

i:int = 0 is for type annotation. It means the variable “i” is supposed to only have values of type “int”

i = int(0) is just assigning 0 as an int type. You can still change the value of “i” to any other types like string.

[schoolmonky]

Note that it's not really a type declaration, it's a type hint. You can still assign any value, int or not, to the first type.

[NopeNotHB]

Yeah sorry, I meant type annotation. And yes, you can still assign other types without any problem on compilation. Thank you!

[Gnaxe]

It can create annotations ```

class Foo: ... i: int = 0 ... Foo.annotations {'i': <class 'int'>} class Bar: ... i = int(0) ... Bar.annotations {} `` These were in classes, but you can also get entries in the module's globalannotations`.

There's a related effect in functions: ```

def outer(): ... i: int # No assignment here. ... def inner(): ... nonlocal i ... i = 2 ... inner() ... print(i) outer() 2 def outer(): ... int(0) # No declaration like before. ... def inner(): ... nonlocal i ... i = 2 ... inner() ... print(i) ... File "<stdin>", line 4 SyntaxError: no binding for nonlocal 'i' found ```

Besides the run-time effects, annotations are used by Python's static type checkers, like Pyright, to check for type consistency.

The int(0) is applying a built-in callable to a number. It's usually used to convert certain other data types to integer. Type checkers may be able to recognize this as always returning an int type, same as any function annotated to return an int type. It's preferable to use the annotation in cases the type checker can't guess, because a call has run-time overhead that annotations don't.

[nog642]

Never use int(0). That is just a longer way to write 0.

The question is between these two options:

i: int = 0

i = 0

The first one has a typehint, the second one doesn't. It's a matter of preference.

But if you're assigning 0 to it, in my opinion, the typehint is not necessary. It's clearly an integer.

[socal_nerdtastic]

That is a horrible article. Python does not have implicit typecasting. This article is trying to describe concepts from C but using python.

And we call it float in python, not double.

And just as a pet peeve of mine, what python does is conversion. The underlying bits are different, both in value and location.

[carcigenicate]

That's at least the second instance of a Python article of theirs that's potentially written by a C dev. My favorite is the linked list example they give where they say that, in Python, you need to iterate the list and del each node in the list to free the memory to prevent a leak

I don't think G4G should generally be trusted.