python – I'm confused about how this code works and how sub-algorithms work

I am confused with how this code works and would appreciate any help. Thank you

def max_factor(num):
    """Find the maximum prime factor."""
    factor = 2
    while factor * factor <= num:
        while num % factor == 0:
            num /= factor
        factor += 1
    if (num > 1):
        return num
    return factor

print max_factor(33) #11
print max_factor(38) #19
print max_factor(600851475143) #6857

unix – Confused by "groups" and the "authorization model" Linux

So I'm trying to understand the concept of groups and permissions in Linux and I am deeply confused. On my laptop, where I'm the only user and therefore the superuser, I understand what it means to change the file permission on text files (chmod + x) to make it executable, or to change read-write permission (chmod + / – rw)

But I don't really understand the concept of a group. From what I have gleaned, a group is just a group of users. (But does that mean that a user can belong to more than one group?) rwx Wholesale permissions for a group of users (i.e. the group).

But now, on this site, the author says:

There are three levels of permissions on Linux: owner, group, and
other. The owner is the user who owns the file / folder, the group
includes other users in the file group and the others simply represent
other users who are neither owners nor members of the group.

Does this mean that in addition to a file with an owner (i.e. the user ID of the person who created the file), there is also a "group owner" for this file? And this group is usually one of the groups
the owner of the file belongs?

What to do if I have three groups A, B and C on my system and want to set permissions rw-, -wx, r-x respectively on the system?

Asking the above questions most likely shows that my mental model of what is a "group" and "group authorization" in Unix is ​​flawed.

I have tried to read a bunch of articles, but there seems to me to be something fundamental missing in understanding the concept of group and group permission.
Can someone give me a brief explanation or refer me to clearer articles on this subject?

dates – Why are people confused? I asked the user the day 05/05/05 or 05/05/05 or 05/05/05?

I just don't know why they can't answer a simple question, what date format are they using: 05/05/05 or 05/05/05 or 05/05/05, why can't they reply?
Here's what I mean, why can't they answer that, and how could I improve that, what I do even that confuses the user when I create a user interface on the date format that & # 39; 39; they use:

areas – Confused about GDPR and who is

The subject of your question is complicated and cannot be repeated in a few sentences.

In summary, the GDPR is still new for many entities, and there are still some phases of adaptation. ICANN (which controls what gTLDs can and cannot do) took a long time to accept that the GDPR did not go away and finally had to take it into account. He created a "temporary specification" for which you can get details at This is why, for the moment, if you look at any gTLD registry that responds, you will generally not see any personal data, more emails, names, Addresses, etc. But it is "temporary". Of course, not everyone is happy with this: LEAs, IP attorneys and others are very keen to revert to the old model … This can (it will appear) in done, because whois will be phased out by RDAP (which has been mandatory in the gTLD world since August 2018), and RDAP being built on a healthier design, can make (where whois couldn't) much easier multi-level access, i.e. having an authentication layer and therefore modifying the amount of results given (with or without personal data, and how much) depending on who interrogates. But we are far from a working model on this scene.

For ccTLDs, each registry must decide what to do, things are unclear. You will find some who are wrong on the side of "show nothing, or almost nothing at all", for example .de (you don't even see the recording date anymore …), then others do the complete opposite, like .IS ( "The Icelandic ccTLD has become what I believe to be the first registry to declare that it will continue to publish email addresses in public Whois records after the General Data Protection Regulation has entered into force. ")

So you can find various articles explaining how the GDPR killed the whois, such as:

You now raise another important point about the "privacy products" of some registrars.

In many (but not all) TLDs, and at least in gTLDs, you have a registry / registrar model: one registry, multiple registrars.

A client goes to a registrar, gives him all his data (including personal and paying for the domain), the registrar stores it locally, also sends it or part of it to the register, which stores it on his side.

This model can then have the consequence (at least because ICANN decided to do so, but there is for the most part no technical reason, because the last thin register in the world gTLD will be "soon" thick like all the others) that there are actually two whois servers (or RDAP for that matter) for a given domain name: a registry side, a registrar side.

Of course, each server responds with locally stored data, but that explains why not everyone can respond with the same data.
Because if you take / buy a "confidentiality" service from the registrar (or a third party), this is what happens:

  • you give your personal data to the registrar; it is stored in its database
  • the registrar sends to the register ANOTHER set of personal data, a blank "confidentiality"; in this way of doing things, the register never sees the "real" data (which has its own set of consequences, because with this the register cannot even know who the real declarer is)
  • so if you query the whois / RDAP server of the registry, you will get at most "confidentiality" data and not the real ones,
  • and if you contact the registrar's whois / RDAP server, while technically it has the real data locally, because you have activated this confidentiality service, the registrar will respond with this confidentiality data instead of the real ones.

And then, as noted above, in addition to a given dataset that should have been provided, the recent changes due to the GDPR, "scrub" the data and essentially create almost empty results.

This is indeed something to take into account if you want to transfer domains between registrars. A previous ICANN rule, for example, in gTLDs, required registrars to get formal and explicitly positive recognition (via some specific emails called FOA for Form Of Authorization ) from the registrar / administrator contact before being able to proceed with a transfer request. This data was mainly extracted from the whois by the registrars, but of course now that the response from the whois is almost empty of substance, it can no longer work (and therefore the transfers revert to their previous model were the exclusive possession of the value "authInfo" because the domain was sufficient to prove ownership and therefore to start transfers).

Typically, registrars will ask you to provide new contact data if you decide to transfer as they will not be able to collect it from the current configuration. When a transfer occurs, nothing changes at the registry level, except who is the registrar. As soon as the transfer is complete, the new registrar is (mainly) free to modify all data, including contacts (but see the new ICANN regulations which deal with a change of registrant essentially in the same way as 39; a change of registrar, with various checks and periods), then reapply, or not (depending on what the registrar provides and what customers have chosen) a confidentiality service as explained above.

Come back to:

I live in the Netherlands and I have a .com domain in Namecheap. According to Namecheap support, my data becomes public in Who is if I deactivate their Who is Guard.

More specifically in .COM, it is always a light register, which means that the register does NOT have contact data (the registrar NEVER sends them to register). This will change, it is expected (but postponed more than once, the question is obviously related to everything that has been discussed previously), but it is like that today. So if you make a whois query for a .COM in the registry, you will never see contact data, no matter which service you enable or disable at the registrar level, because the registry has no data contact for the domain.

Now, at the registrar level, they are "free" to do whatever they want, I mean they can have their own interpretation of the GDPR, how much that applies to them or not, etc.

At least on one of their pages, they say this:

When you register a domain, ICANN asks registrars to provide it
with your contact details (such as name, e-mail, address and telephone)
number). This is then added to the Whois database. This database lists
the owners of each domain name online, and it can be searched by
anyone on the Internet.

It's not very clear to me or maybe a little wrong: I don't know who "them" is in the first sentence, but if it is supposed to be ICANN then it & # 39; s 39 is completely wrong, ICANN has no operational role in daily registrations, so they have no data. There is also no "Whois database" even if everyone makes this mistake. whois is a protocol for querying data. The database queried is in a registry or registrar, and is not a "whois database" in the same way that you use HTTP to contact web servers, but it does Suddenly does not make websites "HTTP databases".
But even apart from that, it cannot really be "searched". whois is a request protocol (RDAP too, and has extensions for real search capabilities, but it should not happen to anyone to implement it for obvious technical and non-technical consequences of this), you ask details on a specific area. You cannot request details of a registrant's name, address or telephone or other numbers. There are various online services providing this type of "reverse lookup" (like: give me a list of domain names owned by "Foo Bar Inc."), and how do they do it? They make whois queries, store the results (in a "database" too), and can therefore search there, but with various limitations (whois is limited in number, their data will never be fresh, several TLDs are against this, see https: / /, etc.)

So I have no idea what happens if you don't use "WhoisGuard". Your supplier should be able to explain the situation clearly to you, and if this is not the case or if you are not satisfied with his response, it will certainly be the right time to report it. look for another.

conspiracy – little confused about taking the transformation

I have a function f, the value of the function at x = 0 is zero and at x = 2, it is one. I am trying to swap this, which means that at x = 0, f should take the value of one and at x = 2 f should be zero. Essentially, I'm trying to reflect my function. I'm trying that. y = f (-x) to reflect around the y axis. What is the appropriate sign change I need to make to achieve this?

f = Sin((((2*0 + 1)*π*(-x))/(2*2)));
Plot(f, {x, 0, 2})  

algebraic geometry – Confused about $ O_X $ ideals and closed subschemes

I am trying to understand a passage from Mumford's Red Book (Section II. 5, page 146 in the old version). Let $ X $ to be a schema, $ Q $ is a sub-sheet of $ O_X $ so that for all $ U $, $ Q (U) $ is an ideal $ O_X (U) $, (I guess it means open $ U $ here) and we call such an object a $ O_X $– ideal.

The part that I'm trying to understand is this: we state that $ Q $ determines closed subschemes up to canonical isomorphisms. First of all, $ Y = {x in X: Q_x neq O_X } $, the sequence
0 to Q_x to O_ {x, X} to O_ {x, Y} to 0

is accurate, and on the other hand $ O_Y $ extended by zero is canonically isomorphic to the cokernel of $ Q to O_X $. So a closed subroutine is really just a $ O_X $-ideal.

I have a hard time seeing how this is explained $ Q $ determines closed subschemes.
I tried to understand some parts of this, so I asked a related question (Question about restoring $ O_X $ – ideal from a $ X $ scheme to an open affine) and it has been mentioned that a near-consistency should be assumed for this, but this does not seem to be assumed here … I would appreciate clarification on this. Thank you.

Confused about the result of my landing page design

I am a beginner in design and stuck when designing this landing page. It is a CV for the software engineer. I wanted to make it minimalist and informative, but I feel like I have to add something. I look forward to receiving comments on this. Link to the site here

8 – Confused with custom field settings

I have a field type plugin with a value of custom parameters (it's a taxonomy vocabulary value), what I want to do is be able to read this field type parameter in the fieldwidget ( maybe also in the trainer, but suspect the same principle will apply)

I can set my field type value OK when adding the field to my content type and this saves OK, but I can't figure out how to get the value in my widget so that I can save it use to retrieve the desired taxonomy terms. The problem is definitely related to the parameters as if I hard coded the desired vocabulary instead of the parameters that my selection list fulfills OK, but I want this to be reusable rather than having to hard code the taxonomy at each time.

Linear algebra – Confused between two methods of calculating the generalized eigenvalue.

For some reason, this issue, in particular, has caused me problems.
I am revising certain notions on eigenvalues, and I am confused between two methods of calculating generalized eigenvalue.

The first method is explained in an example on Wikipedia here

The second is explained here

In other words, should I start by calculating $ (A- lambda I) ^ {m} $ and found $ mathbf {x} _ {m} $ such as $ (A- lambda I) ^ {m} mathbf {x} _ {m} = mathbf {0} $ . Or it's good to start $ (A- lambda I) mathbf {x} _ {2} = mathbf {x} _ {1} $ and go to step $ (A- lambda I) mathbf {x} _ {m} = mathbf {x} _ {m-1} $ or $ mathbf {x} _ {1} $ is an eigenvector

Any help is greatly appreciated

Confused about AF, AF-S (Nikon Autofocus)

I have a Nikon D610. I thought it would work with AF lenses, but my Nikkor AF 50mm 1.8 D does not focus automatically,
Ditto for the Yongnuo 50mm 1.8 AF (the Yongnuo has an MF / AF switch on the lens).
Are these lenses incompatible with the 610's autofocus, operator error, or …?
AF-S autofocus lenses without difficulty.