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1. • • Applied to a function with one variable, the Y combinator usually does not terminate. More interesting results are obtained by applying the Y combinator to functions of two or more variables. The additional variables may be used as a counter, or index. The resulting function behaves like a while or a for loop in an imperative language.
     en.wikipedia.org › wiki › Fixed-point_combinator

     Fixed-point combinator - Wikipedia

2. Top results related to what does y combinator do in python 3

   • What does "nonlocal" do in Python 3?

     Top Answer

     Answered Mar 10, 2022 · 662 votes

     Compare this, without using nonlocal:

     x = 0def outer(): x = 1 def inner(): x = 2 print("inner:", x) inner() print("outer:", x)outer()print("global:", x)# inner: 2# outer: 1# global: 0

     To this, using nonlocal

     , where inner()'s x is now also outer()'s x:

     x = 0def outer(): x = 1 def inner(): nonlocal x x = 2 print("inner:", x) inner() print("outer:", x)outer()print("global:", x)# inner: 2# outer: 2# global: 0

     If we were to use global

     , it would bind x to the properly "global" value:

     x = 0def outer(): x = 1 def inner(): global x x = 2 print("inner:", x) inner() print("outer:", x)outer()print("global:", x)# inner: 2# outer: 1# global: 2

     Other Answers

     Answered Aug 11, 2009 · 130 votes

     In short, it lets you assign values to a variable in an outer (but non-global) scope. See PEP 3104 for all the gory details.

     Other Answers

     Answered Aug 11, 2009 · 56 votes

     A google search for "python nonlocal" turned up the Proposal, PEP 3104, which fully describes the syntax and reasoning behind the statement. in short, it works in exactly the same way as the global statement, except that it is used to refer to variables that are neither global nor local to the function.

     Here's a brief example of what you can do with this. The counter generator can be rewritten to use this so that it looks more like the idioms of languages with closures.

     def make_counter(): count = 0 def counter(): nonlocal count count += 1 return count return counter

     Obviously, you could write this as a generator, like:

     def counter_generator(): count = 0 while True: count += 1 yield count

     But while this is perfectly idiomatic python, it seems that the first version would be a bit more obvious for beginners. Properly using generators, by calling the returned function, is a common point of confusion. The first version explicitly returns a function.

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     1/5

   • What does "for x in y or z:" do in Python?

     Top Answer

     Answered Nov 15, 2013 · 18 votes

     Doing:

     for x in y or z:-

     is the same as:

     for x in (y or z):

     If y evaluates to True, the for-loop will iterate through it. Otherwise, it will iterate through z.

     Below is a demonstration:

     >>> y = [1, 2, 3]>>> z = [4, 5, 6]>>> for x in y or z:... print x...123>>> y = [] # Empty lists evaluate to False in Python>>> for x in y or z:... print x...456>>>

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     2/5

   • What does x in range(...) == y mean in Python 3?

     Top Answer

     Answered Feb 09, 2018 · 14 votes

     This is due to the fact that both operators are comparison operators, so it is being interpreted as operator chaining:

     https://docs.python.org/3.6/reference/expressions.html#comparisons

     Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).

     So it is equivalent to:

     >>> (1 in range(2)) and (range(2) == True)False-

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     3/5

   • What does the `as` command do in Python 3.x?

     Top Answer

     Answered Sep 29, 2013 · 9 votes

     It's not a command per se, it's a keyword used as part of the with

     statement:

     with open("myfile.txt") as f: text = f.read()-

     The object after as gets assigned the result of the expression handled by the with context manager.

     Another use is to rename an imported module:

     import numpy as np-

     so you can use the name np instead of numpy from now on.

     The third use is to give you access to an Exception object:

     try: f = open("foo")except IOError as exc: # Now you can access the Exception for more detailed analysis

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     4/5

   • What does 'from dot import asterisk' do in Python 3?

     Top Answer

     Answered Sep 03, 2019 · 4 votes

     When __main__ is a script or interactive session, . is the __main__ package itself:

     $ python3 -c 'from . import float'Traceback (most recent call last): File "<string>", line 1, in <module>ImportError: cannot import name 'float' from '__main__' (unknown location)-

     This makes from . import * a noop, with __warningregistry__ added as a side-effect of the import machinery.

     Relative imports from __main__ were special-cased by PEP 366. This introduced __package__ for relative package name lookup, and specifies that __main__. __package__ has the special value None.

     In addition, the module import spec __main__.__spec__

     may be None

     - namely in an interactive shell or when executing a script.

     As it turns out, any module with __package__ = __spec__ = None will treat . as itself:

     $ cat test.py__package__ = __spec__ = Nonefrom . import float$ python3 -c 'import test'Traceback (most recent call last): File "<string>", line 1, in <module> File "/Users/mfischer/PycharmProjects/lispy/test.py", line 2, in <module> from . import floatImportError: cannot import name 'float' from 'test' (./test.py)

     The __warningregistry__

     is added because there is a hidden warning from the missing attributes. It is suppressed by default, but you can see it with all warning enabled:

     $ python3 -Wa -c 'from . import float'-c:1: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__Traceback (most recent call last): File "<string>", line 1, in <module>ImportError: cannot import name 'float' from '__main__' (unknown location)

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     5/5

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3. People also ask

   What is a Y-Combinator function?

   • An Y-combinator is a "functional" (or a higher-order function — a function that operates on other functions) that takes a single argument, which is a function that isn't recursive, and returns a version of the function which is recursive. Somewhat recursive =), but more in-depth definition:

   functional programming - What is a Y-combinator? - Stack Overflow

   stackoverflow.com/questions/93526/what-is-a-y-combinator

   See all results for this question

   What is Y-Combinator in Python?

   • Y-combinator in Python :: map(learn, world) A brief introduction to lambda calculus Lambda calculus is a language (formal system) to abstract and express calculation itself under only three concise rules. Syntax Name Description x Variable Representing some value (λx.

   Y-combinator in Python :: map(learn, world)

   kigawas.me/posts/y-combinator-in-python/

   See all results for this question

   What is a Y-Combinator in JavaScript?

   • With some general knowledge presented by other answers, you can begin to pick apart what is happening. The Y function is the "y-combinator". Now take a look at the var factorial line where Y is used. Notice you pass a function to it that has a parameter (in this example, recurse) that is also used later on in the inner function.

   functional programming - What is a Y-combinator? - Stack Overflow

   stackoverflow.com/questions/93526/what-is-a-y-combinator

   See all results for this question

   How does Y Combinator work?

   • The Y Combinator can take a non-recursive function like fact_nr and convert it to a true recursive version. Here is the Y Combinator definition in the form usually found in literature It is pretty daunting to look at. If you are interested in how it works in detail, check out the reference section below.

   Y Combinator in Python

   www.playfulpython.com/y-combinator-in-python/

   See all results for this question

4. lptk.github.io › simple-essence-y-combinatorThe Y Combinator Explained in Python - GitHub Pages

   lptk.github.io › simple-essence-y-combinator

   • Cached

   Oct 15, 2019 · def fact(x): if x == 0: return 1 else: return fact(x - 1) * x. To see how it works, consider that fact(3) computes fact(2) * 3 which is fact(1) * 2 * 3 == fact(0) * 1 * 2 * 3 == 1 * 1 * 2 * 3 == 6. For brevity, we’ll write it in a style that’s a bit more functional: def fact(x): return 1 if x == 0 else fact(x - 1) * x.

5. www.playfulpython.com › y-combinator-in-pythonY Combinator in Python - Playful Python

   www.playfulpython.com › y-combinator-in-python

   • Cached

   Aug 22, 2022 · Y Combinator. The Y Combinator can take a non-recursive function like fact_nr and convert it to a true recursive version. Here is the Y Combinator definition in the form usually found in literature. def Y(fn_nr): return (lambda x: fn_nr(lambda y: x(x)(y)))(lambda x: fn_nr(lambda y: x(x)(y))) or in a simpler form

6. stackoverflow.com › questions › 93526What is a Y-combinator? [closed] - Stack Overflow

   stackoverflow.com › questions › 93526

   • Cached

   Jul 16, 2011 · Y-combinator is a fixed-point combinator. Fixed point of a function is an element of the function's domain that is mapped to itself by the function. That is to say, c is a fixed point of the function f(x) if f(c) = c. This means f(f(...f(c)...)) = fn(c) = c.

   Code sample

   public static Func<T, TResult> Y<T, TResult>(Func<Func<T, TResult>, Func<T, TResult>> F) {

     return

     t =>

     F(

     Y(F)...

   See more on stackoverflow

7. kigawas.me › posts › y-combinator-in-pythonY-combinator in Python :: map(learn, world)

   kigawas.me › posts › y-combinator-in-python

   • Cached

   Nov 22, 2018 · What is Y-combinator⌗ In terms of the functional programming field, Y-combinator is expressed on the lambda calculus format: λf. (λx. (f (x x))) (λx. (f (x x))). With Y-combinator, we can implement recursion without defining functions explicitly. As you may know, recursion is equivalent to iteration, thus we can assure that lambda calculus ...

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9. ycombinator.dev › what-is-ycombinatorUnderstanding Y Combinator: A Guide to the Startup Accelerator

   ycombinator.dev › what-is-ycombinator

   • Cached

   Mar 15, 2024 · Y Combinator (YC) is a name that resonates across the startup ecosystem, known for being a catalyst that propels small startups into global powerhouses. Serving as a launchpad for companies like Airbnb, Dropbox, Stripe, and Reddit, Y Combinator has become synonymous with innovation, networking, and success in the startup world.

10. softwareengineering.stackexchange.com › questionsWhat are combinators and how are they applied to programming ...

    softwareengineering.stackexchange.com › questions

    • Cached

    Some useful ones are twice(f) = \x -> f(f(x)), flip(op)-> \x y -> y op x, (.) as in (f.g) x = f(g(x)), ($) can help with map(called <$> in infix) as in ($5) <$> [(+1), (*2)] = [6, 10], curry can be used in Lisp/Python/JavaScript for partial application, and uncurry can be used for functions that require records(tuples) in Haskell.

11. medium.com › @jnkrtech › an-introduction-to-functionAn Introduction to Function Fixed Points with the Y-Combinator

    medium.com › @jnkrtech › an-introduction-to-function

    • Cached

    Jul 15, 2017 · Follow. 7 min read. ·. Jul 15, 2017. 36. The Y-combinator is a function that lets us do something neat: it allows us to encapsulate recursion in functions. This article shows how this...