Assuming That X Is 1 Show The Result Of The Following Boolean Expressions
Georgeanna Abson
A coworker and I have tried to work this out and the closest thing we could come up with is that the statement is being evaluated by order of precedence. According to the MDN Operator Precedence logical-and has a higher precidence over logical-or, suggesting that the condition is evaluated as if false && true were a single statement, which then moves on to determine the boolean condition of false true which is then true. Written out, this would be:
I've added a bounty because none of the answers given truly understand the question. As stated above: the MDN Logical Operators page states exactly: "false && anything is short-circuit evaluated to false."
I am using here parenthesis as a way to show that the rest of logical expression should have been evaluated independently of "false" part. If it's evaluated independently then short-circuiting it works fine because false && == false.
I should note this: short-circuiting will never ever change the answer. It is an optimization that is made. Since && can only evaluate to true if both operands are true, it won't bother checking what the second operand is if the first is false because it already knows the answer is false. A reciprocal optimization is done with : if the first operand is true, it'll return true without considering the value of the second operand. This optimization exists so that your code will run faster - it will never change the answer. The only reason it's mentioned in MDN at all is because if your && has one operand that will take a lot longer to calculate than the other, you aught to list it second. (It's also important because if takesALongTimeToDetermine() does something besides just return a value, IE, if it prints a log statement that you're expecting, you won't see it if the function is short-circuited. But this still has nothing to do with the answer returned by &&.)
Your interpretation is incorrect, and you're correct that the operator precedence is why it evaluates to true. What you're missing is the meaning of anything in the context of an abstract syntax tree.
The "false" and "anything" in "false && anything" are absolutely referring to Javascript expressions/values (as diagrammed in @Erbureth's answer) , not to your source code. Here are examples to prove this statement:
Hopefully these inane examples help to clarify why it is meaningless to apply the rule you are citing to source code. The rule meant to be applied to the value/subtrees that result after parsing the source code (at which time order of operations have been applied)
This tutorial shows you how to use string interpolation to format and include expression results in a result string. The examples assume that you are familiar with basic C# concepts and .NET type formatting. If you are new to string interpolation or .NET type formatting, check out the interactive string interpolation tutorial first. For more information about formatting types in .NET, see Formatting types in .NET.
To identify a string literal as an interpolated string, prepend it with the $ symbol. You can embed any valid C# expression that returns a value in an interpolated string. In the following example, as soon as an expression is evaluated, its result is converted into a string and included in a result string:
Beginning with .NET 6, you can use the String.Create(IFormatProvider, DefaultInterpolatedStringHandler) method to resolve an interpolated string to a culture-specific result string, as the following example shows:
In earlier versions of .NET, use implicit conversion of an interpolated string to a System.FormattableString instance and call its ToString(IFormatProvider) method to create a culture-specific result string. The following example shows how to do that:
Beginning with .NET 6, use the String.Create(IFormatProvider, DefaultInterpolatedStringHandler) method to resolve an interpolated string to a result string for the InvariantCulture, as the following example shows:
This tutorial describes common scenarios of string interpolation usage. For more information about string interpolation, see String interpolation. For more information about formatting types in .NET, see the Formatting types in .NET and Composite formatting articles.
In Python, operators are special symbols, combinations of symbols, or keywords that designate some type of computation. You can combine objects and operators to build expressions that perform the actual computation. So, operators are the building blocks of expressions, which you can use to manipulate your data. Therefore, understanding how operators work in Python is essential for you as a programmer.
In programming, an operator is usually a symbol or combination of symbols that allows you to perform a specific operation. This operation can act on one or more operands. If the operation involves a single operand, then the operator is unary. If the operator involves two operands, then the operator is binary.
In this code snippet, the minus sign (-) in the first example is a unary operator, and the number 273.15 is the operand. In the second example, the same symbol is a binary operator, and the numbers 5 and 2 are its left and right operands.
Programming languages typically have operators built in as part of their syntax. In many languages, including Python, you can also create your own operator or modify the behavior of existing ones, which is a powerful and advanced feature to have.
So, what is an expression anyway? Python has simple and compound statements. A simple statement is a construct that occupies a single logical line, like an assignment statement. A compound statement is a construct that occupies multiple logical lines, such as a for loop or a conditional statement. An expression is a simple statement that produces and returns a value.
In the first two examples, you use the addition and division operators to construct two arithmetic expressions whose operands are integer numbers. In the last example, you use the equality operator to create a comparison expression. In all cases, you get a specific value after executing the expression.
The assignment operator is one of the most frequently used operators in Python. The operator consists of a single equal sign (=), and it operates on two operands. The left-hand operand is typically a variable, while the right-hand operand is an expression.
In this code snippet, you first create two new variables, a and b, holding 5 and 2, respectively. Then you use these variables to create different arithmetic expressions using a specific operator in each expression.
In the first example, 10 is evenly divisible by 5. Therefore, this operation could return the integer 2. However, it returns the floating-point number 2.0. In the second example, 10.0 is a floating-point number, and 5 is an integer. In this case, Python internally promotes 5 to 5.0 and runs the division. The result is a floating-point number too.
The Python comparison operators allow you to compare numerical values and any other objects that support them. The table below lists all the currently available comparison operators in Python:
The comparison operators are all binary. This means that they require left and right operands. These operators always return a Boolean value (True or False) that depends on the truth value of the comparison at hand.
Probably, the more straightforward comparisons in Python and in math are those involving integer numbers. They allow you to count real objects, which is a familiar day-to-day task. In fact, the non-negative integers are also called natural numbers. So, comparing this type of number is probably pretty intuitive, and doing so in Python is no exception.
In the first set of examples, you define two variables, a and b, to run a few comparisons between them. The value of a is less than the value of b. So, every comparison expression returns the expected Boolean value. The second set of examples uses two values that are equal, and again, you get the expected results.
The math module from the standard library provides a function conveniently called isclose() that will help you with float comparison. The function takes two numbers and tests them for approximate equality:
The uppercase "A" has a lower Unicode point than the lowercase "a". So, "A" is less than "a". In the end, Python compares characters using integer numbers. So, the same rules that Python uses to compare integers apply to string comparison.
The comparison uses lexicographical ordering, which means that Python compares the first item from each string. If their Unicode code points are different, this difference determines the comparison result. If the Unicode code points are equal, then Python compares the next two characters, and so on, until either string is exhausted:
In this example, Python compares both operands character by character. When it reaches the end of the string, it compares "o" and "O". Because the lowercase letter has a greater Unicode code point, the first version of the string is greater than the second.
In this example, Python runs a character-by-character comparison as usual. If it runs out of characters, then the shorter string is less than the longer one. This also means that the empty string is the smallest possible string.
In your Python journey, you can also face the need to compare lists with other lists and tuples with other tuples. These data types also support the standard comparison operators. Like with strings, when you use a comparison operator to compare two lists or two tuples, Python runs an item-by-item comparison.
Python has three Boolean or logical operators: and, or, and not. They define a set of operations denoted by the generic operators AND, OR, and NOT. With these operators, you can create compound conditions.
You can also find Python built-in and custom functions that return a Boolean value. This type of function is known as a predicate function. The built-in all(), any(), callable(), and isinstance() functions are all good examples of this practice.
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