This question already has answers here:
Why isn't the 'len' function inherited by dictionaries and lists in Python
(7 answers)
Why does Python code use len() function instead of a length method?
(7 answers)
In Python, when should I use a function instead of a method?
(5 answers)
Difference between len() and .__len__()?
(5 answers)
Closed 4 years ago.
In Python, why are some built-in functions called using brackets with the method name before the object, e.g.
print("foobar")
bool("foobar")
...
While others are built-in method attributes, called with a dot behind the object, e.g.
"foobar".capitalize()
Specifically I'm interested to learn if there is a general principle behind this instead of just common practice and memorization. In cases where you can't quite remember whether it was capitalize("foobar") or "foobar".capitalize(), how do you know?
Related
This question already has answers here:
How to implement built-in sum() of the class?
(2 answers)
Define "sum" for a class using non-associative addition
(2 answers)
Closed 9 months ago.
Is there any way I can over write the sum() method to act differently on a list?
I expected I would be able to find a dunder method that would allow me to define my own implementation, but I couldn't.
That's how I'd imagine the implementation
class MyDummyList(list):
def __sum__(self): -> str:
return 'a'
x = MyDummyList()
print(sum(x)) -> # prints 'a'
Obviously this breaks as there is no dunder method __sum__ but I am somewhat surprised that there is no such a way to do that using dunder methods as sum is a quite common operation on iterables.
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What does -> mean in Python function definitions?
(11 answers)
Python3 function definition, arrow and colon [duplicate]
(3 answers)
What does the -> (dash-greater-than arrow symbol) mean in a Python method signature? [duplicate]
(1 answer)
Closed 9 months ago.
I'm analyzing some old code that I've inherited, and I have a question about the use of "self" and "None" keywords, specifically in the following example:
def run(self) -> None:
I understand that the self keyword is similar to the "this" keyword in C++ in that, in conjunction with the dot operator, it allows us to access the attributes and methods of the class in question. What I'm really interested in is the use of "-> None" in the declaration of the method named "run." Is this in PEP 8 because I can't find an example. I'm using Python 3.7, in case that matters.
What is the purpose of writing a method in this manner? What does "-> None" do?
They're called type hints, and they enable annotating the types of the parameters and return types of functions.
https://peps.python.org/pep-0484/
This question already has answers here:
python: class override "is" behavior
(4 answers)
Is it possible to get a list of keywords in Python?
(7 answers)
Closed 4 years ago.
I know that in python we can use __eq__ method to check equality and __iter__ when using in keyword. Is there any method for is keyword?
This question already has answers here:
Bare asterisk in function parameters?
(6 answers)
What is the purpose of class methods?
(18 answers)
Closed 5 years ago.
Looking into the Python documentation, I came across the following page:
https://docs.python.org/3/library/stdtypes.html#int.from_bytes
Here, the third argument of int.from_bytes() is *. What does * represent and why can it be ignored in the examples?
Also, the fromkeys(seq[, value]) method is said to be a classmethod, but what exactly does this mean? What class does this method belong to?
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Is there a builtin identity function in python?
(10 answers)
Closed 7 years ago.
In functional programming is sometimes useful to have an identity function.
Is there a built-in or a function defined in some module that does this?
The identity function can be simply defined as:
identity = lambda x: x
I'm not aware of this function defined in any module, but it could be a good fit for functools.