Does True Equal to 1 and False Equal to 0

Is true == 1 and false == 0 in JavaScript?

It's true that true and false don't represent any numerical values in Javascript.

In some languages (e.g. C, VB), the boolean values are defined as actual numerical values, so they are just different names for 1 and 0 (or -1 and 0).

In some other languages (e.g. Pascal, C#), there is a distinct boolean type that is not numerical. It's possible to convert between boolean values and numerical values, but it doesn't happen automatically.

Javascript falls in the category that has a distinct boolean type, but on the other hand Javascript is quite keen to convert values between different data types.

For example, eventhough a number is not a boolean, you can use a numeric value where a boolean value is expected. Using if (1) {...} works just as well as if (true) {...}.

When comparing values, like in your example, there is a difference between the == operator and the === operator. The == equality operator happily converts between types to find a match, so 1 == true evaluates to true because true is converted to 1. The === type equality operator doesn't do type conversions, so 1 === true evaluates to false because the values are of different types.

Is False == 0 and True == 1 an implementation detail or is it guaranteed by the language?

In Python 2.x this is not guaranteed as it is possible for True and False to be reassigned. However, even if this happens, boolean True and boolean False are still properly returned for comparisons.

In Python 3.x True and False are keywords and will always be equal to 1 and 0.

Under normal circumstances in Python 2, and always in Python 3:

False object is of type bool which is a subclass of int:

    object
       |
     int
       |
     bool

It is the only reason why in your example, ['zero', 'one'][False] does work. It would not work with an object which is not a subclass of integer, because list indexing only works with integers, or objects that define a __index__ method (thanks mark-dickinson).

Edit:

It is true of the current python version, and of that of Python 3. The docs for python 2 and the docs for Python 3 both say:

There are two types of integers: [...] Integers (int) [...] Booleans (bool)

and in the boolean subsection:

Booleans: These represent the truth values False and True [...] Boolean values behave like the values 0 and 1, respectively, in almost all contexts, the exception being that when converted to a string, the strings "False" or "True" are returned, respectively.

There is also, for Python 2:

In numeric contexts (for example when used as the argument to an arithmetic operator), they [False and True] behave like the integers 0 and 1, respectively.

So booleans are explicitly considered as integers in Python 2 and 3.

So you're safe until Python 4 comes along. ;-)

1 = false and 0 = true?

It is common for comparison functions to return 0 on "equals", so that they can also return a negative number for "less than" and a positive number for "greater than". strcmp() and memcmp() work like this.

It is, however, idiomatic for zero to be false and nonzero to be true, because this is how the C flow control and logical boolean operators work. So it might be that the return values chosen for this function are fine, but it is the function's name that is in error (it should really just be called compare() or similar).

How to convert 'false' to 0 and 'true' to 1?

Use int() on a boolean test:

x = int(x == 'true')

int() turns the boolean into 1 or 0. Note that any value not equal to 'true' will result in 0 being returned.

Why is True equal to -1

When you cast any non-zero number to a Boolean, it will evaluate to True. For instance:

Dim value As Boolean = CBool(-1) ' True
Dim value1 As Boolean = CBool(1) ' True
Dim value2 As Boolean = CBool(0) ' False

However, as you point out, any time you cast a Boolean that is set to True to an Integer, it will evaluate to -1, for instance:

Dim value As Integer = CInt(CBool(1)) ' -1

The reason for this is because -1 is the signed-integer value where all of its bits are equal to 1. Since a Boolean is stored as a 16-bit integer, it is easier to toggle between true and false states by simply NOT'ing all of the bits rather than only NOT'ing the least significant of the bits. In other words, in order for True to be 1, it would have to be stored like this:

True  = 0000000000000001
False = 0000000000000000

But it's easier to just store it like this:

True  = 1111111111111111
False = 0000000000000000

The reason it's easier is because, at the low-level:

1111111111111111 = NOT(0000000000000000)

Whereas:

0000000000000001 <> NOT(0000000000000000)
0000000000000001 = NOT(1111111111111110)

For instance, you can replicate this behavior using Int16 variables like this:

Dim value As Int16 = 0
Dim value2 As Int16 = Not value
Console.WriteLine(value2) ' -1

This would be more obvious if you were using unsigned integers, because then, the value of True is the maximum value rather than -1. For instance:

Dim value As UInt16 = CType(True, UInt16) ' 65535

So, the real question, then, is why in the world does VB.NET use 16 bits to store a single bit value. The real reason is speed. Yes, it uses 16 times the amount of memory, but a processor can do 16-bit boolean operations a lot faster than it can do single-bit boolean operations.

Side note: The reason why the Int16 value of -1 is stored as 1111111111111111 instead of as 1000000000000001, as you might expect (where the first bit would be the "sign bit", and the rest would be the value), is because it is stored as the two's-complement. Storing negative numbers as the two's-complement means that arithmetic operations are much easier for the processor to perform. It's also safer because, with two's-compliment, there's no way to represent 0 as a negative number, which could cause all sorts of confusion and bugs.

Is it guaranteed that False is 0 and True is 1?

It is part of the language specification, so any Python implementation should implement the booleans as equivalent to the integers.

Booleans

These represent the truth values False and True. The two objects representing the values False and True are the only Boolean objects. The Boolean type is a subtype of plain integers, and Boolean values behave like the values 0 and 1, respectively, in almost all contexts, the exception being that when converted to a string, the strings "False" or "True" are returned, respectively.

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