I know that the operators is and is not test for object identity: x is y is true if and only if x and y are the same object     I initialize two variables i and j with the same value 10, and when I am comparing the id of both variable with is operator it gives me a False   even though the id(i) and id(j) are the same.   I need a clarification, Here is my code  &gt;&gt;&gt; i = 10; &gt;&gt;&gt; j = 10; &gt;&gt;&gt; print(10==10); True &gt;&gt;&gt; print(id(10)==id(10)); True &gt;&gt;&gt; print(10 is 10); True &gt;&gt;&gt; print(5+5 is 10); True &gt;&gt;&gt; print(i == j); True &gt;&gt;&gt; print(id(i) == id(j)); True &gt;&gt;&gt; print(i is j); True &gt;&gt;&gt; print(id(i) is id(j)); # Why this statment Evaluate to False this is my quetion? False &gt;&gt;&gt; id(i); 140718000878704 &gt;&gt;&gt; id(j); 140718000878704
2525
My  has failed me.  In Python, are the following two tests for equality equivalent?  n = 5 # Test one. if n == 5:     print 'Yay!'  # Test two. if n is 5:     print 'Yay!'   Does this hold true for objects where you would be comparing instances (a list say)?  Okay, so this kind of answers my question:  L = [] L.append(1) if L == [1]:     print 'Yay!' # Holds true, but...  if L is [1]:     print 'Yay!' # Doesn't.   So == tests value where is tests to see if they are the same object?
93
I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?
18487
Let  $A$ and $B$  be matrices over $\mathbb C$. Then,          $AB$  and $BA$   always have the same set of eigenvalues.      If  $AB$  and  $BA$  have the same set of eigenvalues then $AB=BA$.           If  $A^{-1}$   exists then  $AB$  and $BA$   are similar.     The rank of  $AB$  is always the same as the  rank of   $BA$ .       Suppose $AB=BA$ Let $x$ be the eigen vector of $A$ corresponding to the eigenvalue $a$. $$ABx=BAx=aBx \implies Bx$$ is the eigen vector of $A$. If the eigen space corresponding to the eigen values of $A$ is one. Then, $Bx=\lambda x \implies x$ is the eigen vector of $B$. So $AB$ and $BA$ have same set of eigen values. statement is false. Am I correct? I don't know, How to judge the statement. I don't know, How to judge the statement. Statement is false, I could obtain the counter examples.   Please check my answers. Please help me.
4398
What is the best way to check whether a given object is of a given type? How about checking whether the object inherits from a given type?  Let's say I have an object o. How do I check whether it's a str?
38840
I have gone through various sources... But I am not quite sure what it is.I want an and gate and the logical equivalent is two inputs feeding to one gate and for Y=AB' the logical equivalent is feeding to one not gate and one and gate. But it is the same LUT for both AND and Y=AB'. I think we store the values as desired in the LUT. Someone elaborate on this
82914
I have some dynamic SOQL code in which I'd like to identify whether a method argument is a collection or a single value:  SObject[] query(SObjectType sobType, String field, Object data) {     // Want to know if data is a collection e.g. set or list     // that requires an "in" or a single value that requires     // an "=" in the query. (May also need to use separate bind variables.) }   I note that the sort of check shown immediately below seems to require an exact match for the type of the collection (Id in this case to return true) which is not what I want:  Object o = new Set&lt;Id&gt;(); System.debug(o instanceof Set&lt;Id&gt;);   Is there a simple way to make this determination?  (Yes there are various other ways to code this; checking first to see if there is a direct solution.)  PS  Looks like great caution is needed when using .
107670
Why is it bad to name a variable id in Python?
36777
What is the difference between == and === in JavaScript?  I have also seen != and !== operators.  Are there more such operators?
1022
The following code works as expected in both Python 2.5 and 3.0:  a, b, c = (1, 2, 3)  print(a, b, c)  def test():     print(a)     print(b)     print(c)    # (A)     #c+=1       # (B) test()   However, when I uncomment line (B), I get an UnboundLocalError: 'c' not assigned at line (A). The values of a and b are printed correctly. This has me completely baffled for two reasons:   Why is there a runtime error thrown at line (A) because of a later statement on line (B)? Why are variables a and b printed as expected, while c raises an error?   The only explanation I can come up with is that a local variable c is created by the assignment c+=1, which takes precedent over the "global" variable c even before the local variable is created. Of course, it doesn't make sense for a variable to "steal" scope before it exists.  Could someone please explain this behavior?
67180
I remember reading in some Java book about any operator other than 'instanceof' for comparing the type hierarchy between two objects.  instanceof is the most used and common. I am not able to recall clearly whether there is indeed another way of doing that or not.
6670
I was wondering how to check whether a variable is a class (not an instance!) or not.  I've tried to use the function isinstance(object, class_or_type_or_tuple) to do this, but I don't know what type would a class will have.  For example, in the following code  class Foo: pass   isinstance(Foo, **???**) # i want to make this return True.   I tried to substitute  "class" with ???, but I realized that class is a keyword in python.
6937
I am sorry if this is quite elementary question. But I always think, that why we use $:=$ at some places, instead of $=$. Is there any fundamental difference between these two? Before reading Terry Tao's blog (4 months ago), I had never seen a symbol like this (:=).
4630
I'm new to Delphi, and I've been running some tests to see what object variables and stack variables are initialized to by default:  TInstanceVariables = class   fBoolean: boolean; // always starts off as false   fInteger: integer; // always starts off as zero   fObject: TObject; // always starts off as nil end;   This is the behaviour I'm used to from other languages, but I'm wondering if it's safe to rely on it in Delphi?  For example, I'm wondering if it might depend on a compiler setting, or perhaps work differently on different machines.  Is it normal to rely on default initialized values for objects, or do you explicitly set all instance variables in the constructor?  As for stack (procedure-level) variables, my tests are showing that unitialized booleans are true, unitialized integers are 2129993264, and uninialized objects are just invalid pointers (i.e. not nil).  I'm guessing the norm is to always set procedure-level variables before accessing them?
106335
What does the following mean?  Class.Function(variable := 1 + 1)   What is this operator called, and what does it do?
6852
What is the difference between below variables assignments?   var=23 var =23 var= 23 var = 23   Is there any difference in space around the assignment operator?
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Given a method signature:  public bool AreTheSame&lt;T&gt;(Expression&lt;Func&lt;T, object&gt;&gt; exp1, Expression&lt;Func&lt;T, object&gt;&gt; exp2)   What would be the most efficient way to say if the two expressions are the same? This only needs to work for simple expressions, by this I mean all that would be "supported" would be simple MemberExpressions, eg c => c.ID.  An example call might be:  AreTheSame&lt;User&gt;(u1 =&gt; u1.ID, u2 =&gt; u2.ID); --&gt; would return true
93154
I'm having problems with this; the strategy is to show the left side is in the right side, and vice versa. Thus far I can only show that both sides of the equality are in A\B. Can I use "the empty set = A and not A" as a fact? Because then it works. Or just show me how to do it!