🔒 Confusion with printing variables

[thorny gale]

Hello,

I recently started learning Python for Data Science purposes but I am already familiar with different coding concepts and the language Java.
Currently, I am trying to understand the data types in java. Weirdly, I cannot print them as expected:

    print("Unsorted list: " + scores.__str__())
    scores.sort()
    print("Sorted list: " + scores.__str__())

Why is it that the method (??) __str__ is necessary here? Is this even a method?
I have seen multiple occurrences of the double underscore but I haven't found any resources about what they mean.

I appreciate your help!

[sharp zenith]

@thorny gale

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[ripe pier]

Look up "Python data model". It will explain what the "dunder methods" are for. __str__ is comparable to Java's toString method though, and you don't typically call it directly. str calls the passed object's __str__ for you.

In short though, dunder methods are used to hook into internal stuff, like defining what an object's length is, and what subscripting means for that object.

[thorny gale]

str(scores) you mean? That seems to work too! I am just more used to using methods of objects rather than methods using objects. : D

[thorny gale]

I will look that up. Thanks a lot 👍

[ripe pier]

Yes. Or just do print("Unsorted", scores) since print automatically converts the arguments to strings. Or use f-strings.

You need str with your current code because +, for strings, requires that both operands be strings (Python is strongly typed).

[thorny gale]

Well that did NOT work

That is what confused me because in java the toString method is usually called automatically

TypeError: can only concatenate str (not "list") to str

Aaaah wait, the comma

[ripe pier]

You're still using +.

[thorny gale]

😓 Sorry 😄

[ripe pier]

Print is a bit of a special case. It's var arg, and converts all arguments to strings, and then by default, joins the arguments on a space.

[thorny gale]

Yup, that worked 👍

[thorny gale]

The space is a bit weird though. Can you disable that?

[ripe pier]

!e

print('a', 'b', sep='')
print('a', 'b', sep='+')

[sharp zenith]

@ripe pier :white_check_mark: Your 3.12 eval job has completed with return code 0.

001 | ab
002 | a+b

[ripe pier]

If you want more control though, just use f-strings.

!f-string

[sharp zenith]

Format-strings

Creating a Python string with your variables using the + operator can be difficult to write and read. F-strings (format-strings) make it easy to insert values into a string. If you put an f in front of the first quote, you can then put Python expressions between curly braces in the string.

>>> snake = "pythons"
>>> number = 21
>>> f"There are {number * 2} {snake} on the plane."
"There are 42 pythons on the plane."

Note that even when you include an expression that isn't a string, like number * 2, Python will convert it to a string for you.

[thorny gale]

Thats neat

[ripe pier]

Yes, print is capable of a ton. It can even be used to write to files using its file parameter.

[thorny gale]

Seemingly a lot more capable than System.out.println() 😆

[ripe pier]

Python flips it. In Java, each file/stream defines its own println iirc (it's been like 5 years since I've written Java). In Python, you pass the file to the one print, and if you don't specify the fill, it defaults to the STDOUT.

But yes, it's capable because it's made for convenience.

[arctic helm]

also 72% less typing :p

though we used to write "sout" and then eclipse was completing it or something

[sharp zenith]

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