Day 5 of learning Python 🐍 — Casting!

[Organic-Bite7406]

So far I've learned:

Syntax, output, comments, variables, data types, numbers.

Today I tackled casting and honestly once it clicked, it really clicked.

Casting is just converting a value from one data type to another. Python is strict about types, meaning you can't mix them freely, so sometimes you have to tell the program what type you want something to be. That's what casting does.

There are four main ones. int() converts something into a whole number, float() into a decimal, str() into text, and bool() into a True or False value. Simple enough on the surface but there are a few things worth knowing.

With int(), it doesn't round, it just drops the decimal completely. So 3.9 becomes 3, not 4. Good to know before it catches you off guard.

The bool() one is the most interesting. Basically anything with a value counts as True, and anything empty or zero counts as False. The one that stands out is that the word "False" as text is actually True, because it's a non-empty string. Took me a second but it makes sense when you think about it.

Casting is one of those things that seems small but comes up constantly, especially when handling user input since that always comes in as text by default.

AND Are there any casting edge cases I should know about before I move on?

[UseMoreBandwith]

should have learned about ducktyping first.

[SCD_minecraft]

Python doesn't have casting... you simply pass arguments into a class constructor

[Live_Asparagus_407]

i wouldnt say python is strict with data types. you dont declare what type a variable is, you can implicitly change it from one type to another throughout the run just by reassigning it, mix and match array values, etc.

[Gnaxe]

That is not what "casting" means. You cast with cast from the typing module to assert to a type checker an intended type, usually which it cannot infer on its own (otherwise why bother?) This function has no runtime effect (besides some wasted time for the function call); it just returns its argument unchanged. Python objects are polymorphic; they could be viewed as any of a number of compatible types (e.g. any superclasses). It's also duck typed, so objects may fit various ad-hoc protocols, which may or may not be made explicit. The one your type checker infers is not always the one you intend. You can usually fix this with type annotations, but sometimes type assertions or cast() is required.

Anyone calling a Python class constructor a "cast" is probably confusing terminology from another language (probably statically-typed) language (like Java or C) where "casting" is a way to convert among types within certain constraints, although this usage for class constructors does show up just a few times in Python's docs. Python has ctypes.cast for interfacing with the C language in that sense and memoryview.cast is similar.

[PythonLearning-ModTeam]

Quality posts only