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   • Under what circumstances are __rmul__ called?

     Top Answer

     Answered Dec 21, 2021 · 171 votes

     When Python attempts to multiply two objects, it first tries to call the left object's __mul__() method. If the left object doesn't have a __mul__() method (or the method returns NotImplemented, indicating it doesn't work with the right operand in question), then Python wants to know if the right object can do the multiplication. If the right operand is the same type as the left, Python knows it can't, because if the left object can't do it, another object of the same type certainly can't either.

     If the two objects are different types, though, Python figures it's worth a shot. However, it needs some way to tell the right object that it is the right object in the operation, in case the operation is not commutative. (Multiplication is, of course, but not all operators are, and in any case * is not always used for multiplication!) So it calls __rmul__() instead of __mul__().

     As an example, consider the following two statements:

     print "nom" * 3print 3 * "nom"-

     In the first case, Python calls the string's __mul__() method. The string knows how to multiply itself by an integer, so all is well. In the second case, the integer does not know how to multiply itself by a string, so its __mul__() returns NotImplemented and the string's __rmul__() is called. It knows what to do, and you get the same result as the first case.

     Now we can see that __rmul__() allows all of the string's special multiplication behavior to be contained in the str class, such that other types (such as integers) do not need to know anything about strings to be able to multiply by them. A hundred years from now (assuming Python is still in use) you will be able to define a new type that can be multiplied by an integer in either order, even though the int class has known nothing of it for more than a century.

     By the way, the string class's __mul__() has a bug in some versions of Python. If it doesn't know how to multiply itself by an object, it raises a TypeError instead of returning NotImplemented. That means you can't multiply a string by a user-defined type even if the user-defined type has an __rmul__() method, because the string never lets it have a chance. The user-defined type has to go first (e.g. Foo() * 'bar' instead of 'bar' * Foo()) so its __mul__() is called. They seem to have fixed this in Python 2.7 (I tested it in Python 3.2 also), but Python 2.6.6 has the bug.

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     1/5

   • Under what circumstances are linked lists useful?

     Top Answer

     Answered May 23, 2017 · 45 votes

     They can be useful for concurrent data structures. (There is now a non-concurrent real-world usage sample below - that would not be there if @Neil hadn't mentioned FORTRAN. ;-)

     For example, ConcurrentDictionary<TKey, TValue> in .NET 4.0 RC use linked lists to chain items that hash to the same bucket.

     The underlying data structure for ConcurrentStack<T> is also a linked list.

     ConcurrentStack<T> is one of the data structures that serve as the foundation for the new Thread Pool, (with the local "queues" implemented as stacks, essentially). (The other main supporting structure being ConcurrentQueue<T>.)

     The new Thread Pool in turn provides the basis for the work scheduling of the new Task Parallel Library.

     So they can certainly be useful - a linked list is currently serving as one of the main supporting structures of at least one great new technology.

     (A singly-linked list makes a compelling lock-free - but not wait-free - choice in these cases, because main operations can be carried out with a single CAS (+retries). In a modern GC-d environment - such as Java and .NET - the ABA problem can easily be avoided. Just wrap items you add in freshly created nodes and do not reuse those nodes - let the GC do its work. The page on the ABA problem also provides the implementation of a lock-free stack - that actually works in .Net (&Java) with a (GC-ed) Node holding the items.)

     Edit: @Neil: actually, what you mentioned about FORTRAN reminded me that the same kind of linked lists can be found in probably the most used and abused data structure in .NET: the plain .NET generic Dictionary<TKey, TValue>.

     Not one, but many linked lists are stored in an array.

     • It avoids doing many small (de)allocations on inserts/deletes.
     • Initial loading of the hash table is pretty fast, because the array is filled sequentially (plays very nice with CPU cache).
     • Not to mention that a chaining hash table is expensive in terms of memory - and this "trick" cuts "pointer sizes" in half on x64.

     Essentially, many linked lists are stored in an array. (one for each bucket used.) A free list of reusable nodes is "interwoven" between them (if there were deletes). An array is allocated at the start/on rehash and nodes of chains are kept in it. There is also a free pointer - an index into the array - that follows deletes. ;-) So - believe it or not - the FORTRAN technique still lives on. (...and nowhere else, than in one of the most commonly used .NET data structures ;-).

     Other Answers

     Answered Mar 11, 2010 · 58 votes

     Linked lists are very useful when you need to do a lot of insertions and removals, but not too much searching, on a list of arbitrary (unknown at compile-time) length.

     Splitting and joining (bidirectionally-linked) lists is very efficient.

     You can also combine linked lists - e.g. tree structures can be implemented as "vertical" linked lists (parent/child relationships) connecting together horizontal linked lists (siblings).

     Using an array based list for these purposes has severe limitations:

     • Adding a new item means the array must be reallocated (or you must allocate more space than you need to allow for future growth and reduce the number of reallocations)
     • Removing items leaves wasted space or requires a reallocation
     • inserting items anywhere except the end involves (possibly reallocating and) copying lots of the data up one position

     Other Answers

     Answered Mar 11, 2010 · 22 votes

     Linked lists are very flexible: With the modification of one pointer, you can make a massive change, where the same operation would be very inefficient in an array list.

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     2/5

   • Under what parameters are SVC and LinearSVC in scikit-learn equivalent?

     Top Answer

     Answered Apr 27, 2020 · 38 votes

     In mathematical sense you need to set:

     SVC(kernel='linear', **kwargs) # by default it uses RBF kernel-

     and

     LinearSVC(loss='hinge', **kwargs) # by default it uses squared hinge loss

     Another element, which cannot be easily fixed is increasing intercept_scaling in LinearSVC, as in this implementation bias is regularized (which is not true in SVC nor should be true in SVM - thus this is not SVM) - consequently they will never be exactly equal (unless bias=0 for your problem), as they assume two different models

     • SVC : 1/2||w||^2 + C SUM xi_i
     • LinearSVC: 1/2||[w b]||^2 + C SUM xi_i

     Personally I consider LinearSVC one of the mistakes of sklearn developers - this class is simply not a linear SVM.

     After increasing intercept scaling (to 10.0)

     However, if you scale it up too much - it will also fail, as now tolerance and number of iterations are crucial.

     To sum up: LinearSVC is not linear SVM, do not use it if do not have to.

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     3/5

   • Under what circumstances are C++ destructors not going to be called?

     Top Answer

     Answered May 23, 2017 · 51 votes

     Are there any other circumstances where they[destructors] will not be called?

     • Long jumps: these interfere with the natural stack unwinding process and often lead to undefined behavior in C++.
     • Premature exits (you already pointed these out, though it's worth noting that throwing while already stack unwinding as a result of an exception being thrown leads to undefined behavior and this is why we should never throw out of dtors)
     • Throwing from a constructor does not invoke the dtor for a class. This is why, if you allocate multiple memory blocks managed by several different pointers (and not smart pointers) in a ctor, you need to use function-level try blocks or avoid using the initializer list and have a try/catch block in the ctor body (or better yet, just use a smart pointer like scoped_ptr since any member successfully initialized so far in an initializer list will be destroyed even though the class dtor will not be called).
     • As pointed out, failing to make a dtor virtual when a class is deleted through a base pointer could fail to invoke the subclass dtors (undefined behavior).
     • Failing to call matching operator delete/delete[] for an operator new/new[] call (undefined behavior - may fail to invoke dtor).
     • Failing to manually invoke the dtor when using placement new with a custom memory allocator in the deallocate section.
     • Using functions like memcpy which only copies one memory block to another without invoking copy ctors. mem* functions are deadly in C++ as they bulldoze over the private data of a class, overwrite vtables, etc. The result is typically undefined behavior.
     • Instantiation of some of smart pointers (auto_ptr) on an incomplete type, see this discussion

     Other Answers

     Answered Mar 11, 2010 · 58 votes

     Linked lists are very useful when you need to do a lot of insertions and removals, but not too much searching, on a list of arbitrary (unknown at compile-time) length.

     Splitting and joining (bidirectionally-linked) lists is very efficient.

     You can also combine linked lists - e.g. tree structures can be implemented as "vertical" linked lists (parent/child relationships) connecting together horizontal linked lists (siblings).

     Using an array based list for these purposes has severe limitations:

     • Adding a new item means the array must be reallocated (or you must allocate more space than you need to allow for future growth and reduce the number of reallocations)
     • Removing items leaves wasted space or requires a reallocation
     • inserting items anywhere except the end involves (possibly reallocating and) copying lots of the data up one position

     Other Answers

     Answered Mar 11, 2010 · 22 votes

     Linked lists are very flexible: With the modification of one pointer, you can make a massive change, where the same operation would be very inefficient in an array list.

     Check all answers on Stack Overflow

     4/5

   • What are the under-the-hood differences between round() and numpy.round()?

     Top Answer

     Answered Dec 04, 2013 · 9 votes

     One on top of the hood difference is documented:

     In cases where you're halfway between numbers, np.round

     rounds to the nearest "even" number (after multiplying by 10**n where n is the second argument to the respective round function) whereas the builtin round

     rounds away from 0.

     >>> np.round(2.685, 2)2.6800000000000002>>> round(2.685, 2)2.69

     Under the hood, you can get differences when using the scaling parameter. Consider the differences between round(2.675 * 10.**2) and round(2.675, 2). This is certainly a result of the floating point math which as always has some rounding error associated with it. To go any further we would really need to look at the real implementation.

     Check all answers on Stack Overflow

     5/5

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2. People also ask

   What companies are under meta?

   • Here are the main companies under Meta: Furthermore, some lesser-known acquisitions include Giphy – a platform for sharing GIFs; Onavo – a mobile analytics company; Redkix – an email startup that was integrated into Workplace by Facebook; Beat Games – creator of Beat Saber game, among others.

   What Companies Does Meta Own: A Comprehensive Guide to Their Por…

   seriosity.com/what-companies-does-meta-own/

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   Is meta a big company?

   • The company owns and operates Facebook, Instagram, Threads, and WhatsApp, among other products and services. Meta ranks among the largest American information technology companies, alongside other Big Five corporations Alphabet ( Google ), Amazon, Apple, and Microsoft. The company was ranked #31 on the Forbes Global 2000 ranking in 2023.

   Meta Platforms - Wikipedia

   en.wikipedia.org/wiki/Meta_Platforms

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   How many companies does meta own?

   • Meta owns 94 companies with total assets of $165.987 billion till 2023, here we listed the top companies owned by Meta. Meta is a multinational American company with headquarters located in Menlo Park, California with a total of 66,185 employees in the year 2023 an increase of 20.9% from 2022.

   List of Companies Owned by META (Facebook) - GeeksforGeeks

   www.geeksforgeeks.org/list-of-companies-owned-by-meta/

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   What products does meta offer?

   • Meta’s main products include social media platforms like Facebook and Instagram, virtual reality devices such as Oculus, and technologies related to the metaverse. And why go anywhere else when our DSA to Development: Coding Guide helps you do this in a single program!

   List of Companies Owned by META (Facebook) - GeeksforGeeks

   www.geeksforgeeks.org/list-of-companies-owned-by-meta/

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3. inspirationfeed.com › what-companies-does-facebook-ownComplete List of Companies Owned By Meta (Facebook)

   inspirationfeed.com › what-companies-does-facebook-own

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   Jul 24, 2023 · Not really. GAFAM simply stands for Google, Amazon, Facebook, Apple, and Microsoft. GAMAM, on the other hand, represents Google, Apple, Meta, Amazon and Microsoft. These are the 5 most valued corporations in the world. Let’s dive into the details and unearth all the companies owned by Facebook.

4. www.geeksforgeeks.org › list-of-companies-owned-byList of Companies Owned by META (Facebook) - GeeksforGeeks

   www.geeksforgeeks.org › list-of-companies-owned-by

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   Mar 4, 2024 · Here are some interesting facts about Facebook (meta): Facebook is one of the biggest tech companies founded by Mark Zuckerberg, which later came to be known as Meta. Meta owns 94 companies with total assets of $165.987 billion till 2023, here we listed the top companies owned by Meta.

5. en.wikipedia.org › wiki › Meta_PlatformsMeta Platforms - Wikipedia

   en.wikipedia.org › wiki › Meta_Platforms

   • Cached

   Meta ranks among the largest American information technology companies, alongside other Big Five corporations Alphabet ( Google ), Amazon, Apple, and Microsoft. The company was ranked #31 on the Forbes Global 2000 ranking in 2023. [15]

   • Founded: January 4, 2004; 19 years ago in Cambridge, Massachusetts, U.S.

   • Type: Public

6. www.investopedia.com › articles › personal-financeTop 5 Companies Owned by Facebook (Meta) - Investopedia

   www.investopedia.com › articles › personal-finance

   • Cached

   • Instagram. Type of Business: Photo and video-sharing app. Acquisition Cost: $1.0 billion. Acquisition Date: April 9, 2012. Instagram is a photo and video-sharing social networking platform that was launched in 2010.
   • WhatsApp. Type of Business: Mobile messenger service. Acquisition Cost: $19.0 billion. Acquisition Date: February 19, 2014. WhatsApp is a messenger and calling service available to users throughout the world.
   • Oculus VR. Type of Business: Virtual reality technology company. Acquisition Cost: $2.0 billion. Acquisition Date: March 25, 2014. Just weeks after announcing its acquisition of WhatsApp, Meta followed up by buying virtual reality hardware and software company Oculus VR.
   • Onavo. Type of Business: Mobile web analytics. Acquisition Cost: $100–200 million (estimated) Acquisition Date: October 2013. Founded in 2010, Israeli company Onavo performs web analytics on other mobile apps to determine customer usage.

7. seriosity.com › what-companies-does-meta-ownWhat Companies Does Meta Own: A Comprehensive Guide to Their ...

   seriosity.com › what-companies-does-meta-own

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   Sep 30, 2023 · Here are the main companies under Meta: Furthermore, some lesser-known acquisitions include Giphy – a platform for sharing GIFs; Onavo – a mobile analytics company; Redkix – an email startup that was integrated into Workplace by Facebook; Beat Games – creator of Beat Saber game, among others.

8. about.fb.com › news › 2021The Facebook Company Is Now Meta | Meta

   about.fb.com › news › 2021

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   Oct 28, 2021 · Introducing Meta: A Social Technology Company. October 28, 2021. Today at Connect 2021, CEO Mark Zuckerberg introduced Meta, which brings together our apps and technologies under one new company brand. Meta’s focus will be to bring the metaverse to life and help people connect, find communities and grow businesses.

9. en.wikipedia.org › wiki › List_of_mergers_andList of mergers and acquisitions by Meta Platforms - Wikipedia

   en.wikipedia.org › wiki › List_of_mergers_and

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   Meta Platforms (formerly Facebook, Inc.) is a technology company that has acquired 91 other companies, including WhatsApp. The WhatsApp acquisition closed at a steep $16 billion; more than $40 per user of the platform. Meta also purchased the defunct company ConnectU in a court settlement and acquired intellectual property formerly held by ...