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How to determine the variable type in Python?

How do I see the type of a variable whether it is unsigned 32 bit, signed 16 bit, etc.?

How do I view it?

What is the difference between bool and Boolean types in C#

What is the difference between bool and Boolean types in C#?

How to find out if a Python object is a string?

How can I check if a Python object is a string (either regular or Unicode)?

typedef struct vs struct definitions

I'm a beginner in C programming, but I was wondering what's the difference between using typedef when defining a structure versus not using typedef. It seems to me like there's really no difference, they accomplish the same.

struct myStruct{
    int one;
    int two;
};

vs.

typedef struct{
    int one;
    int two;
}myStruct;

How to check if type of a variable is string in python?

Is there a way to check if the type of a variable in python is string.. like

isinstance(x,int);

for integer values?

What is the purpose of a question mark after a type (for example: int? myVariable)?

typically the main use of the question mark is for the conditional, x ? "yes" : "no".

But I have seen another use for it but can't find an explanation of this use of the ? operator, for example.

public int? myProperty
  {
   get;
   set;
  }

How do I check that a number is float or integer?

How to find that a number is float or integer?

1.25 --> float  
1 --> integer  
0 --> integer  
0.25 --> float

Differences between isinstance() and type() in python

What are the differences between these two code fragments? Which way is considered to be more pythonic?

Using type():

import types

if type(a) is types.DictType:
    do_something()
if type(b) in types.StringTypes:
    do_something_else()

Using isinstance():

if isinstance(a, dict):
    do_something()
if isinstance(b, str) or isinstance(b, unicode):
    do_something_else()

Edit: This seems to be discussed already: link.

When to use NSInteger vs. int

When should I be using NSInteger vs. int when developing for iOS? I see in the Apple sample code they use NSInteger (or NSUInteger) when passing a value as an argument to a function or returning a value from a function.

- (NSInteger)someFunc;...
- (void)someFuncWithInt:(NSInteger)value;...

But within a function they're just using int to track a value

for (int i; i < something; i++)
...

int something;
something += somethingElseThatsAnInt;
...

I've read (been told) that NSInteger is a safe way to reference an integer in either a 64-bit or 32-bit environment so why use int at all?

String vs string in C# [duplicate]

Possible Duplicate:
In C# what is the difference between String and string

In C# the string keyword (highlighted in Visual Studio as a data type) is just a shortcut to the String class right?

In that case, it would be the same to use either while coding from the semantic point of view. However, is it the same from the performance point of view? I mean, when the mapping is performed: during compilation (I guess so), during compilation or during JIT compilation in execution?

Or maybe this is all wrong: string and String are not the same thing in C# so there are some situations where they cannot be interchanged

Should you choose the MONEY or DECIMAL(x,y) datatypes in SQL Server?

I'm curious as to whether or not there is a real difference between the money datatype and something like decimal(19,4) (which is what money uses internally, I believe).

I'm aware that money is specific to SQL Server. What I want to know is if there is a compelling reason to choose one over the other; most SQL Server samples (e.g. the AdventureWorks database) use money and not decimal for things like price information.

Should I just continue to use the money datatype, or is there a benefit to using decimal instead? Money is fewer characters to type but that's not a valid reason :)

PostgreSQL: Difference between text and varchar (character varying)

What's the difference between the text data type and the character varying (varchar) data types?

According to the documentation

If character varying is used without length specifier, the type accepts strings of any size. The latter is a PostgreSQL extension.

and

In addition, PostgreSQL provides the text type, which stores strings of any length. Although the type text is not in the SQL standard, several other SQL database management systems have it as well.

So what's the difference?

python: list vs tuple, when to use each? [duplicate]

In Python, when should you use lists and when tuples?

Sometimes you don't have a choice, for example if you have

"hello %s you are %s years old" % x

then x must be a tuple.

But if I am the one who designs the API and gets to choose the data types, then what are the guidelines?

In C#, how do I check if a type is a subtype OR the type of an object?

To check if a type is a subclass of another type in C#, it's easy:

typeof (SubClass).IsSubclassOf(typeof (BaseClass)); // returns true

However, this will fail:

typeof (BaseClass).IsSubclassOf(typeof (BaseClass)); // returns false

Is there any way to check whether a type is either a subclass OR of the base class itself, without using an OR operator or using an extension method?

What does the `forall` keyword in Haskell/GHC do?

I'm beginning to understand how the forall keyword is used in so-called "existential types" like this:

data ShowBox = forall s. Show s => SB s

This is only a subset, however, of how forall is used and I simply cannot wrap my mind around its use in things like this:

runST :: forall a. (forall s. ST s a) -> a

Or explaining why these are different:

foo :: (forall a. a -> a) -> (Char,Bool)
bar :: forall a. ((a -> a) -> (Char, Bool))

Or the whole RankNTypes stuff...

I tend to prefer clear, jargon-free English rather than the kinds of language which are normal in academic environments. Most of the explanations I attempt to read on this (the ones I can find through search engines) have these problems:

1. They're incomplete. They explain one part of the use of this keyword (like "existential types") which makes me feel happy until I read code that uses it in a completely different way (like runST, foo and bar above).
2. They're densely packed with assumptions that I've read the latest in whatever branch of discrete math, category theory or abstract algebra is popular this week. (If I never read the words "consult the paper whatever for details of implementation" again, it will be too soon.)
3. They're written in ways that frequently turn even simple concepts into tortuously twisted and fractured grammar and semantics.

So...

On to the actual question. Can anybody completely explain the forall keyword in clear, plain English (or, if it exists somewhere, point to such a clear explanation which I've missed) that doesn't assume I'm a mathematician steeped in the jargon?

Edited to add:

There were two stand-out answers from the higher-quality ones below, but unfortunately I can only choose one as best. Norman's answer was detailed and useful, explaining things in a way that showed some of the theoretical underpinnings of forall and at the same time showing me some of the practical implications of it. yairchu's answer covered an area nobody else mentioned (scoped type variables) and illustrated all of the concepts with code and a GHCi session. Were it possible to select both as best, I would. Unfortunately I can't and, after looking over both answers closely, I've decided that yairchu's slightly edges out Norman's because of the illustrative code and attached explanation. This is a bit unfair, however, because really I needed both answers to understand this to the point that forall doesn't leave me with a faint sense of dread when I see it in a type signature.