3.1.1.2 Making decisions in Python

Questions and answers

A programmer writes a program and the program asks questions.

A computer executes the program and provides the answers. The program must be able to react according to the received answers.

Fortunately, computers know only two kinds of answers:

• yes, this is true;
• no, this is false.

You will never get a response like Let me think...., I don't know, or Probably yes, but I don't know for sure.

To ask questions, Python uses a set of very special operators. Let's go through them one after another, illustrating their effects on some simple examples.

Comparison: equality operator

Question: are two values equal?

To ask this question, you use the == (equal equal) operator.

Don't forget this important distinction:

• = is an assignment operator, e.g., a = b assigns a with the value of b;
• == is the question are these values equal?; a == b compares a and b.

It is a binary operator with left-sided binding. It needs two arguments and checks if they are equal.

Exercises

Now let's ask a few questions. Try to guess the answers.

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Question #1: What is the result of the following comparison?

2 == 2    

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Question #2: What is the result of the following comparison?

2 == 2.    

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Question #3: What is the result of the following comparison?

1 == 2