python-course | write clean , maintainable and scalable code
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How to write clean, maintainable and scalable code on Python:.
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QUESTION
When a divide-and-conquer recursive function doesn't yield runtimes low enough, which other improvements could be done?
Let's say, for example, this power
function taken from here:
ANSWER
Answered 2021-Jun-15 at 17:36The primary optimization you should use here is common subexpression elimination. Consider your first piece of code:
QUESTION
This is a very basic question relating to setting attributes that I don't find a definitive answer to. I have a python class as follows
...ANSWER
Answered 2021-Mar-20 at 22:51The second option is confusing, as you said, because you would need to go to the method definition to understand there is an assignment to a new variable in the class instance. The first option is somewhat clearer in that sense, but I would still like to know what is the necessary input arguments to that method.
The third option however is wrong for two reasons. One, you pass the radius but you still access self.radius, so the argument is redundant. Second, even if you use the argument, it's supposed to be a static method decorated with @staticmethod, because you don't use the class instance (self).
Therefore, I would go with a static method that utilizes the proper input variables it needs. Something like:
QUESTION
I have a Networkx graph like the following image (image source)
I perform edge attacks and observe the change in values at the node of the resulting subgraph.
Example, If I attack edge (a,2): edge (a, 2) and (2, 1) will be removed. To explain a bit, when edge (a, 2) is attacked the node 2 will have a degree < 2. So the edge that's connected to node 2 is also removed.
The above attack results in a subgraph
Each time an edge is attacked, the value of the terminal node labelled e
observed over time changes. Let's say I perform 5 (attack = 5) attacks, I have a time x attack
matrix (time=25, attack=5) that stores the time-series data of node e
.
I would like to ask for suggestions on how to visualize the effect of these attacks on the value of node e
changing over time.
EDIT:
What information do you want to be able to see or identify from your visualizations?
I want to see the attack on which edge has the maximum effect on the time course value observed at e
. We could imagine this to be a transportation network and the values at node reflect the amount of a product that has reached the location/node. From the source node b
, the goods are transported to target node e
. The observation made is the change in node values after an edge is attacked and no observation of the edge value is available.
Please find the code that is used to attack edges
...ANSWER
Answered 2020-Sep-08 at 14:37Prior to deleting the node add arrows to the edges pointing towards node e
, node and edges to be removed in green, then red, and repeat. Alphas can also be incorporated to represent min-max distances and how they change as the graph is modified.
NetworkX directed graph example: https://networkx.github.io/documentation/stable/auto_examples/drawing/plot_directed.html
NetworkX draw_networkx_edges arguments (includes arrow, color and alpha): https://networkx.github.io/documentation/stable/reference/generated/networkx.drawing.nx_pylab.draw_networkx_edges.html
QUESTION
Is it possible to overload arbitrary operators in Python? Or is one restricted to the list of operators which have associated magic methods as listed here: https://www.python-course.eu/python3_magic_methods.php ?
I'm asking because I noticed that Numpy uses the @ operator to perform matrix multiplication e.g. C=A@B where A,B are Numpy arrays, and I was wondering how they did it.
Edit: The @ operator is not in the list I linked to.
Could someone point me to the Numpy source where this is done?
...ANSWER
Answered 2020-Jul-10 at 10:08In Python, you cannot create new operators, no. By defining those "magic" functions, you can affect what happens when objects of your own definition are operated upon using the standard operators.
However, the list you linked to is not complete. In Python 3.5, they added special methods for the @
operator. Here's the rather terse listing in the Python operator module docs and here are the docs on operator overloading.
operator.matmul(a, b)
operator.__matmul__(a, b)
Return
a @ b
.New in version 3.5.
I hadn't seen that operator personally, so I did a little more research. It's intended specifically for matrix multiplication. But, I was able to use it for other purposes, though I would argue against doing so as a matter of style:
QUESTION
I'm refreshing my memory about some python features that I didn't get yet, I'm learning from this python tutorial and there's an example that I don't fully understand. It's about a decorator counting calls to a function, here's the code:
...ANSWER
Answered 2017-Jul-07 at 10:26What I don't get here is why do we increment the calls of the function wrapper (helper.calls += 1) instead of the function calls itself, and why does it actually working?
I think to make it a generically useful decorator. You could do this
QUESTION
MAIN TROUBLE
As an example, say I would like to decorate split()
method of str
class
(the example is representative of what I try to do, except I would like to decorate agg
method of pandas DataFrame
class).
At least, I get the same error.
I prefer not to use @
nor to create a child of str
class to keep things simple (and maybe it is why it is not working...)
I encounter following trouble.
...ANSWER
Answered 2020-May-09 at 14:52Ok, just found out thanks to this explanation: https://www.bogotobogo.com/python/python_differences_between_static_method_and_class_method_instance_method.php
Another way of calling is by going through the class name as shown below:
Here is the working code.
QUESTION
In this example below, the method m
on class A
is called just once.
I understand this is a feature, this is the Pythonic way to solve the issue where A
's m
method would be called twice (if it was implemented in the naive way) in this diamond-like inheritance scenario.
This is all described here:
https://www.python-course.eu/python3_multiple_inheritance.php
(1) But under the hood... how did they achieve this behavior i.e. that class A
's m
method is called ONLY once?!
Asked simplistically: which line is being "skipped" during execution - is it line #1
or line # 2
?
Could someone shed more light on this?
I have never used multiple inheritance seriously because I mostly program in Java. So I am really curious about this scenario here and more specifically to the inner-workings behind it.
Note: I just want to get the general idea of how this works in Python, not really understand every tiny detail here.
(2) What if I want (in this same scenario and for some reason) A
's m
method to be called twice (or N
times depending on how many base classes of D
we have), while still going through using super()
. Is this possible? Does super()
support such mode of operation?
(3) Is this just some tree or DAG visiting algorithm where they keep track which class's m
method has already been visited and just don't visit it (call it) twice? If so then simplistically speaking I guess '# 2' is the line which is skipped.
ANSWER
Answered 2020-Apr-28 at 18:35This has to do with the Method Resolution Order, which the article you linked already provided some insight (and more information from this other article as well):
The question arises how the super functions makes its decision. How does it decide which class has to be used? As we have already mentioned, it uses the so-called method resolution order(MRO). It is based on the C3 superclass linearisation algorithm. This is called a linearisation, because the tree structure is broken down into a linear order. The mro method can be used to create this list:
QUESTION
First post on Overstack.
I'm new to Python and coding in general. I'm now learning about functions and presently looking at some examples that describe global variables on Python-Course.eu:
...ANSWER
Answered 2020-Apr-24 at 08:22It's reasonably straightforward, as per the Python FAQ (with my emphasis):
In Python, variables that are only referenced inside a function are implicitly global. If a variable is assigned a value anywhere within the function’s body, it’s assumed to be a local unless explicitly declared as global.
So, if you assign to a variable anywhere within a function, that variables is considered local everywhere in the function, leading to issues such as:
QUESTION
I am trying to write a class that allows me to record the number of zip files in a location and store that list as an attribute so I can reference it repeatedly. I don't want the check for zip files to be run automatically when the class is initialized because it takes a long time (it does more than what's written here). I have written that but now I would like to expand it with new features. I would like to add two features to it. First, I would also like the ability to recheck the path after setting the attribute (imagine I've created the class then moved more files into the directory). And secondly, I would like the ability to change the directory I look for the zip files in. Here is my original class:
...ANSWER
Answered 2020-Mar-18 at 00:43Add a reset()
method that sets self.zip_files_at_loc_
back to None
, so the next call will recalculate.
And make the directory a parameter of the class. To change directories just use different C
objects for each. Or reassign c.default_path()
and then call c.reset()
.
QUESTION
I have seen other posts that say just add extra dimensions as it expects. Firstly, I don't know how to do that exactly, but most importantly, I want to know why my dimensions are changing so I can figure this out on my own for future models.
Note, I am restricted to only MLP for training. This means only Fully Connected layers. No Convolutional Layers nor feedbacks are allowed (LSTM or any RNN architecture). No pre-trained models are allowed such as (resnet, densenet, ...). I can use other operations in-between layers, like Dropout, Batch Normalization or other types of layer input/output manipulation. I expect I will have to supply my entire code to get the help I need. Please forgive all my comments in my code, which I have as a reminder to me as to what everything does. I do know I will need data augmentation, but need this to work first.
...ANSWER
Answered 2020-Mar-13 at 17:33The problem here is that you flatten out for normalization and forgot to reshape it to the same old shape (this line train_data = train_data.reshape(len(train_data), -1),test_data = test_data.reshape(len(test_data), -1)
) which is you flatten out all dimension except first dimension and then you use its old dimension (before you flatten out) as an input dimension (input_shape = (nRows, nCols, nDims), inputs = Input(shape=input_shape)
)
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