CODEWITHSUNDEEP
pythonboolean
Steve Smith
Steve Smith

Reputation: 101

Struggling with the order of operations. Am I overthinking this?

I've been given the following, and I'm asked to give the type of value and the expression it returns:

>>> b = 10

>>> c = b > 9

>>> c

I know that in the first part, we're defining b to be 10, but in the second sentence, I'm interpreting this as: Define c to be equal to b>9. Now b>9 as a value, doesn't make sense, so c can't be equal to it, so I put that the answer was error and the type was Nonetype.

The correct answer is apparently True, but why? Why do we take the c=b part first, and then ask whether it's >9? Is there some sort of standard order in which you're supposed to apply these things?

PS: What do the three >>> symbols mean in programming? I'm doing an introductory CS course, so please forgive any misnomers.

Upvotes: 0

Views: 56

Answers (2)

OneCricketeer
OneCricketeer

Reputation: 191864

Python's order precedence is well documented. b > 9 returns a boolean value that must be evaluated before it can be assigned with c =.

And >>> is part of the interpreter REPL. It doesn't have a specific meaning to all programming languages.

You could run your code in any Python interpreter to see what the output values are. I'm not sure what you mean by getting a Nonetype error as nothing is evaluated to None in those lines

Upvotes: 1

James Bateson
James Bateson

Reputation: 1237

I think you're getting confused between:

  • the assignment operator (=), which assigns the result of the expression on the right side of the operator to the variable on the left side of the operator and;
  • the equality operator (==), which tests the expressions on the right and left of the operator for equality and returns a boolean (true/false) value.

The first expression assigns the value 10 to the variable b. The second expression assigns the expression b > 9 (i.e. 10 > 9), which evaluates to true, to c. Therefore, I hope you can see how c ends up being true.

The other issue you might need clarification on is that the = operator is right associative, which means that the expression to the right of the operator will be evaluated first. i.e. in the second line, b > 9 is evaluated first before assigning the result (true) to c.

In answer to the second part of your question. Your code wouldn't actually compile as it stands in a regular C# compiler. I'm not sure what the >>> are. Are you using an online editor or something?

Valid C# code would be:

int b = 10;
bool c = b > 9;
Console.WriteLine(c); //Outputs true

Upvotes: 0

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