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What does -> mean in Python function definitions?
...to attach a metadata string to various types of object. This is amazingly handy, so Python 3 extends the feature by allowing you to attach metadata to functions describing their parameters and return values.
There's no preconceived use case, but the PEP suggests several. One very handy one is to al...
What does the “at” (@) symbol do in Python?
...
An @ symbol at the beginning of a line is used for class, function and method decorators.
Read more here:
PEP 318: Decorators
Python Decorators
The most common Python decorators you'll run into are:
@property
@classmethod
@staticmethod
If you see an @ in the middle of a line, that's ...
Is arr.__len__() the preferred way to get the length of an array in Python?
...5
The same works for tuples:
my_tuple = (1,2,3,4,5)
len(my_tuple)
# 5
And strings, which are really just arrays of characters:
my_string = 'hello world'
len(my_string)
# 11
It was intentionally done this way so that lists, tuples and other container types or iterables didn't all need to expl...
Approximate cost to access various caches and main memory?
Can anyone give me the approximate time (in nanoseconds) to access L1, L2 and L3 caches, as well as main memory on Intel i7 processors?
...
Difference between a theta join, equijoin and natural join
I'm having trouble understanding relational algebra when it comes to theta joins, equijoins and natural joins. Could someone please help me better understand it? If I use the = sign on a theta join is it exactly the same as just using a natural join?
...
Object of custom type as dictionary key
...
You need to add 2 methods, note __hash__ and __eq__:
class MyThing:
def __init__(self,name,location,length):
self.name = name
self.location = location
self.length = length
def __hash__(self):
return hash((self.name, self.lo...
Inherit docstrings in Python class inheritance
I'm trying to do some class inheritance in Python. I'd like each class and inherited class to have good docstrings. So I think for the inherited class, I'd like it to:
...
Print all properties of a Python Class [duplicate]
...ordered results. If you need to print for example in order of declaration, and you do not want to do it manually, check this
– Matteo A
Aug 14 '15 at 8:41
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Serializing class instance to JSON
I am trying to create a JSON string representation of a class instance and having difficulty. Let's say the class is built like this:
...
Accessing dict keys like an attribute?
... Unless - of course - you assign some value to them, see below)
Attributes and items are always in sync
Trying to access non-existent key as an attribute correctly raises AttributeError instead of KeyError
Supports [Tab] autocompletion (e.g. in jupyter & ipython)
Cons:
Methods like .keys() wil...