abulafia's questions

When writing answers for Stack Overflow it is a good idea to test your code before publishing it. In some cases to replicate the questioner's problem I have to install extra packages.

I find it very useful for cases like this to use Google Colab to quickly install the packages I need, write code, test it, and finally write an answer, all without having to install anything locally on my computer. I then manually copy and paste the Colab code into SO, but that can introduce errors or inconsistencies.

Ideally, you would be able to develop a full, tested response in Colab and then automatically somehow "export" what was written there for inclusion in an SO response.

As far as I know in Jupyter Notebook there is a command to export to markdown, is there an automatic way to achieve the same in Google Colab, considering that there is no access to the file .ipynb?

An algorithm for approximating decimals of pi is raised in a recent question . The algorithm basically boils down to iterating the following recurrence relation:

num_iter = 10
a = 0
i = 1
while i <= num_iter:
  a = sqrt(2+a)
  x = sqrt(2-a)
  pi = x * 2**(i+1)
  i += 1

This relation works well for low values ​​of num_iter, but rounding errors begin to occur, which was the objective of that question, and which can be corrected using fixed-point representations ( decimal), at the cost of increasing the memory needed.

My question now is what algorithm is this that is being used? I couldn't find references to it. On the other hand it doesn't seem to be a very good algorithm (as was shown in the answer to that question) What other algorithms are better for computing pi? In what way are they better?

In a recent question on the site, a meme about certain expressions in a programming language is shown, asking how one of them works.

The meme was the following:

The question was how it worked i -=- 1. However, the one that really caught my attention was the last one: i = ~-idoes this really serve the same purpose as the previous ones, that is, to increase iby 1?

If so how does it work?

A recent question, which didn't specify what language/technology I wanted to solve it with, prompted me to think about how I would do it with Pandas.

The question can be rephrased in the context of Pandas as follows.

Given a dataframe such as the one I build here:

import pandas as pd
datos = [["jose", "manzana"],
         ["andres","pera"],
         ["luis", "pera"],
         ["jose", "manzana"]]
df = pd.DataFrame(datos, columns=["Nombre", "Fruta"])
print(df)

Which looks like this:

   Nombre    Fruta
0    jose  manzana
1  andres     pera
2    luis     pera
3    jose  manzana

I want to obtain another one in which the index is the names (without repetitions), the columns are the fruits, and the cells are the number of times each name appears with each fruit. Namely:

Fruta   manzana  pera
Nombre               
andres        0     1
jose          2     0
luis          0     1

my attempt

It seems that this is asking for a pivot_table(), but in order to solve it I have not thought of another way than to add to the original dataframe an extra column full of 1:

>>> print(df.assign(Cuantas=1))
   Nombre    Fruta  Cuantas
0    jose  manzana        1
1  andres     pera        1
2    luis     pera        1
3    jose  manzana        1

In order to use that column as a value to add in the pivot_table. So my solution looks like this:

sol = df.assign(Cuantas=1).pivot_table(
        index="Nombre", 
        columns="Fruta", 
        values="Cuantas", 
        aggfunc="sum", 
        fill_value=0)

and indeed this gives the desired result, but it seems a bit cumbersome to me.

The question is , is there an easier way? .

I am rephrasing this question from another user, because the original one was unsolvable and the question will possibly be closed, but I think the general technique to solve it might be interesting.

It is essentially about completing the following text, so that the MD5 hash of the complete text is equal to a given one. This is the incomplete text:

with an iron rod) that there are too many redundancies and that only the argument should suffice. What I can say is my name. My name is ......."

We are given the following data:

1. The missing word at the end (which I have represented by .......) has 7 letters, all capital ascii.
2. That word starts with Aand ends with O.
3. The MD5 hash of the final text, encoded in CP-1252, must be7292e0ae2227b2fd1cb089656aeff5e2

What is the missing word?

In a question that will probably be closed due to its low quality and the user's lack of interest, the following text was pasted, clearly incorrect because "strange" characters appeared instead of accented vowels or eñes:

with an iron rod) that there are too many redundancies and that only the argument should suffice. What I can say is my name. My name is"

Apparently the user received a text with some unknown encoding , opened it in an editor that used another (also unknown) encoding and copied and pasted what that editor showed him into the question.

Probably your operator, regardless of the encoding used by your editor, converted the text to Unicode in order to save it to the clipboard, and therefore the version that was finally pasted into the question is the UTF-8 representation of those Unicode characters.

The question is how could the original encoding of the data be determined? in order to restore the text as it should look.