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• Optimizing a memoization decorator not increase call stack

  - by Tyler Crompton

  I have a very, very basic memoization decorator that I need to optimize below: def memoize(function): memos = {} def wrapper(*args): try: return memos[args] except KeyError: pass result = function(*args) memos[args] = result return result return wrapper The goal is to make this so that it doesn't add on to the call stack. It actually doubles it right now. I realize that I can embed this on a function by function basis, but that is not desired as I would like a global solution for memoizing. Any ideas?

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• why do I need the @ for setting variable value

  - by Saad

  I'm a little confused about scope of variables, in ruby I wrote a test program: class Test attr_reader :tester def initialize(data) @tester = data end def getData tester end end puts Test.new(11).getData now this works fine, the attr_reader, but my confusion is that since I've define attr_reader :tester then why can't I go tester = data rather then @tester = data, because when retrieving the data in getData I only have to write tester and not @tester

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• What's the difference between these two calls to a function taking a collection of structural types?

  - by James Moore

  Why does the call to fn(Iterator("foo") compile, but the call to fn(fooIterator) fail with an error "type mismatch; found : Iterator[java.lang.String] required: scala.Iterator[com.banshee.Qx.HasLength]" object Qx { type HasLength = {def length: Int} def fn(xs: Iterator[HasLength]) = 3 var tn = fn(Iterator("foo")) var fooIterator = Iterator("foo") var tnFails = fn(fooIterator) //doesn't compile } Aren't they the same thing?

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• C++ DLL Export: Decorated/Mangled names

  - by Bob

  Created basic C++ DLL and exported names using Module Definition file (MyDLL.def). After compilation I check the exported function names using dumpbin.exe I expect to see: SomeFunction but I see this instead: SomeFunction = SomeFunction@@@23mangledstuff#@@@@ Why? The exported function appears undecorated (especially compared to not using the Module Def file), but what's up with the other stuff? If I use dumpbin.exe against a DLL from any commercial application, you get the clean: SomeFunction and nothing else......

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• Mutable global variables don't get hide in python functions, right?

  - by aXqd

  Please see the following code: def good(): foo[0] = 9 # why this foo isn't local variable who hides the global one def bad(): foo = [9, 2, 3] # foo is local, who hides the global one for func in [good, bad]: foo = [1,2,3] print('Before "{}": {}'.format(func.__name__, foo)) func() print('After "{}": {}'.format(func.__name__, foo)) The result is as below: # python3 foo.py Before "good": [1, 2, 3] After "good": [9, 2, 3] Before "bad" : [1, 2, 3] After "bad" : [1, 2, 3]

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• Connecting slots and events in PyQt4 in a loop

  - by LukaD

  Im trying to build a calculator with PyQt4 and connecting the 'clicked()' signals from the buttons doesn't as expected. Im creating my buttons for the numbers inside a for loop where i try to connect them afterwards. def __init__(self): for i in range(0,10): self._numberButtons += [QPushButton(str(i), self)] self.connect(self._numberButtons[i], SIGNAL('clicked()'), lambda : self._number(i)) def _number(self, x): print(x) When I click on the buttons all of them print out '9'. Why is that so and how can i fix this?

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• Named parameters lead to inferior readability?

  - by Thomas Jung

  With named parameters like def f(x : Int = 1, y : Int = 2) = x * y your parameter names become part of the interface f(x=3) Now if you want to change the parameter names locally, you are forced to perserve the public name of the parameter: def f(x : Int = 1, y : Int = 2) = { val (a,b) = (x,y) a * b } If this a real problem? Is there a syntax to support this directly? Who do other languages handle this?

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• Strange behaviour of keywords within macros in Clojure

  - by mikera

  I'm a little confused by how keyword accesses seem to behave in Clojure when they are evaluated at macro expansion time. The following works as I expect: (def m {:a 1}) (:a m) => 1 However the same keyword access doesn't seem to work within a macro: (def m {:a 1}) (defmacro get-a [x] (:a x)) (get-a m) => nil Any idea what is going on here?

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• How do I add a decorator to a method in python?

  - by Timmy

  How do I add a decorator to a method in a class? I tried def add_decorator( cls ): @dec def update(self): pass cls.update = update @dec did not apply to update I'm trying to use this with orm.reconstructor in sqlalchemy.

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• how to send some data to the Thread module on python and google-map-engine

  - by zjm1126

  from google.appengine.ext import db class Log(db.Model): content = db.StringProperty(multiline=True) class MyThread(threading.Thread): def run(self,request): #logs_query = Log.all().order('-date') #logs = logs_query.fetch(3) log=Log() log.content=request.POST.get('content',None) log.put() def Log(request): thr = MyThread() thr.start(request) return HttpResponse('') error is : Exception in thread Thread-1: Traceback (most recent call last): File "D:\Python25\lib\threading.py", line 486, in __bootstrap_inner self.run() File "D:\zjm_code\helloworld\views.py", line 33, in run log.content=request.POST.get('content',None) NameError: global name 'request' is not defined

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• Metaprogramming ActiveRecord Rails

  - by Dimitar Vouldjeff

  Hi, I have the following code in my project`s lib directory module Pasta module ClassMethods def self.has_coordinates self.send :include, InstanceMethods end end module InstanceMethods def coordinates [longitude ||= 43.0, latitude ||= 25.0] end end ActiveRecord::Base.extend ClassMethods end And it should create a class method for ActiveRecord::Base - has_coordinates - which I can "assign" to models... But I receive the error undefined local variable or method 'has_coordinates' Thanks in advance!

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• How can I memoize a method that may return true or false in Ruby?

  - by Seamus Abshere

  Obviously ||= won't work def x? @x_query ||= expensive_way_to_calculate_x end because if it turns out to be false, then expensive_way_to_calculate_x will get run over and over. Currently the best way I know is to put the memoized true or false into an Array: def x? return @x_query.first if @x_query.is_a?(Array) @x_query = [expensive_way_to_calculate_x] @x_query.first end Is there a more conventional or efficient way of doing this?

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• Proc.new vs Lambda in Ruby

  - by piemesons

  Plese check this: def foo f = Proc.new { return "return from foo from inside proc" } f.call # control leaves foo here return "return from foo" end def bar f = lambda { return "return from lambda" } f.call # control does not leave bar here return "return from bar" end puts foo # prints "return from foo from inside proc" puts bar # prints "return from bar" Can anybody tell me what lambda is and what is Proc and whats the difference.

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• Python function argument scope (Dictionaries v. Strings)

  - by Shaun Meyer

  Hello, given: foo = "foo" def bar(foo): foo = "bar" bar(foo) print foo # foo is still "foo"... foo = {'foo':"foo"} def bar(foo): foo['foo'] = "bar" bar(foo) print foo['foo'] # foo['foo'] is now "bar"? I have a function that has been inadvertently over-writing my function parameters when I pass a dictionary. Is there a clean way to declare my parameters as constant or am I stuck making a copy of the dictionary within the function? Thanks!

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• Can I detect tautologies at compile time?

  - by Tim Gradwell

  Is there any way I can catch tautologies at compile time? Such as if (abc && abc) or if (def || def)

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• Python, invoke super constructor

  - by Mike

  class A: def __init__(self): print "world" class B(A): def __init__(self): print "hello" B() hello In all other languages I've worked with the super constructor is invoked implicitly. How does one invoke it in Python? I would expect super(self) but this doesn't work

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• Why can I not access this class member in python?

  - by Peter Smit

  I have the following code class Transcription(object): WORD = 0 PHONE = 1 STATE = 2 def __init__(self): self.transcriptions = [] def align_transcription(self,model,target=Transcription.PHONE): pass The important part here is that I would like to have a class member as default value for a variable. This however gives the following error: NameError: name 'Transcription' is not defined Why is this not possible and what is the right (pythonic) way to do something like this.

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• Which style of return is "better" for a method that might return None?

  - by Daenyth

  I have a method that will either return an object or None if the lookup fails. Which style of the following is better? def get_foo(needle): haystack = object_dict() if needle not in haystack: return None return haystack[needle] or, def get_foo(needle): haystack = object_dict() try: return haystack[needle] except KeyError: # Needle not found return None I'm undecided as to which is more more desirable myself. Another choice would be return haystack[needle] if needle in haystack else None, but I'm not sure that's any better.

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• Python: How to get the caller's method name in the called method?

  - by ziang

  Python: How to get the caller's method name in the called method? Assume I have 2 methods: def method1(self): ... a = A.method2() def method2(self): ... If I don't want to do any change for method1, how to get the name of the caller (in this example, the name is method1) in method2?

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• Any way to make DataContractJsonSerializer serialize Dictionaries properly?

  - by morpheus

  The DataContractJsonSerializer is not able to serialize Dictionaries properly. Whereas JavaScriptSerializer serializes Dictionaries as {"abc":"xyz","def":42} for example, the DataContractJsonSerializer gives [{"Key":"abc","Value":"xyz"},{"Key":"def","Value":42}] instead. This is really problematic and I want to know how can I serialize Dictionary objects correctly in my WCF service. I am looking for a solution that would require least amount of effort. ref: http://msdn.microsoft.com/en-us/library/bb412170.aspx

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• Ruby Module Inclusion in Methods

  - by Federico Builes

  In class Foo I'd like to include method Bar under certain conditions: module Bar def some_method "orly" end end class Foo def initialize(some_condition) if !some_condition "bar" else class << self; include Bar; end end end end Is there any cleaner (and clearer) way to achieve the include in the method without having to do it inside the singleton class?

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• Python required variable style

  - by Adam Nelson

  What is the best style for a Python method that requires the keyword argument 'required_arg': def test_method(required_arg, *args, **kwargs: def test_method(*args, **kwargs): required_arg = kwargs.pop('required_arg') if kwargs: raise ValueError('Unexpected keyword arguments: %s' % kwargs) Or something else? I want to use this for all my methods in the future so I'm kind of looking for the best practices way to deal with required keyword arguments in Python methods.

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• undefined method `parameterize' for nil:NilClass

  - by Senthil

  I've been trying to do SEO friendly urls, and managed to get it work, but when I call index action on blogs, I get a weird "undefined method `parameterize' for nil:NilClass." The method works when using show method. def to_s title end def to_param "#{id}-#{to_s.parameterize}" end

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• How to get search results in grails if you have the domain (model) name stored in a string

  - by Shekhar

  I have a method which has domain name as a String parameter. def modelName="Equity" I want to use it like def results=modelName.findAll() Please guide me!

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• python and palindromes

  - by tekknolagi

  i recently wrote a method to cycle through /usr/share/dict/words and return a list of palindromes using my ispalindrome(x) method here's some of the code...what's wrong with it? it just stalls for 10 minutes and then returns a list of all the words in the file def reverse(a): return a[::-1] def ispalindrome(a): b = reverse(a) if b.lower() == a.lower(): return True else: return False wl = open('/usr/share/dict/words', 'r') wordlist = wl.readlines() wl.close() for x in wordlist: if not ispalindrome(x): wordlist.remove(x) print wordlist

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