Equality: the equal to operator (==)
The == (equal to) operator compares the values of two operands. If they are equal, the result of the comparison is True. If they are not equal, the result of the comparison is False.
Look at the equality comparison below - what is the result of this operation?
var == 0
Note that we cannot find the answer if we do not know what value is currently stored in the variable var.
If the variable has been changed many times during the execution of your program, or its initial value is entered from the console, the answer to this question can be given only by Python and only at runtime.
Now imagine a programmer who suffers from insomnia, and has to count black and white sheep separately as long as there are exactly twice as many black sheep as white ones..
The question will be as follows:
black_sheep == 2 * white_sheep
Due to the low priority of the == operator, the question shall be treated as equivalent to this one:
black_sheep == (2 * white_sheep)
So, let's practice your understanding of the == operator now - can you guess the output of the code below?
var = 0 # Assigning 0 to var
print(var == 0)
var = 1 # Assigning 1 to var
print(var == 0)
True
False
Run the code and check if you were right.
Inequality: the not equal to operator (!=)
The != (not equal to) operator compares the values of two operands, too. Here is the difference: if they are equal, the result of the comparison is False. if they are not equal, the result of the comparison is True.
Now take a look at the inequality comparison below - can you guess the result of this operation?
var = 0 # Assigning 0 to var
print(var != 0)
var = 1 # Assigning 1 to var
print(var != 0)
Run the code and check if you were right.
Comparison operators: greater than
You can also ask a comparison question using the > (greater than) operator.
If you want to know if there are more black sheep than white ones, you can write it as follows:
black_sheep > white_sheep # Greater than
True confirms it; False denies it
Comparison operators: greater than or equal to
The greater than operator has another special, non-strict variant, but it's denoted differently than in classical arithmetic notation: >= (greater than or equal to).
There are two subsequent signs, not one.
Both of these operators (strict and non-strict), as well as the two others discussed in the net section, are binary operators with left-sided binding, and their priority is greater than that shown by == and !=
If we want to find out whether or not we have to wear a warm hat, we ask the following question:
centigrade_outside ≥ 0.0 # Greater than or equal to
Comparison operators: less than or equal to
As you've probably already guessed, the operators used in this case are: the < (less than) operator and its non-strict sibling: <= (less than or equal to).
Look at this simple example:
current_velocity_mph < 85 # Less than
current_velocity_mph ≤ 85 # Less than or equal to
We're going to check if there's risk of being fined by the highway police (the first question is strict, the second isn't)
Making use of athe answers
What can you do with the answer (i.e., the result of a comparison operation) you get from the computer?
The content of the variable will tell you the answer to the question asked.
The second possibility is more convenient and far more commo: you can use the answer you get to make a decision about the future of the program.
You need a special instruction for this purpose, and we'll discuss it very soon.
Now we need to update our priority table, and put all the new operators into it. It now looks as follows:
PriorityOperator
1+, -unary
2**
3*, /, //, %
4+, -binary
5<, <=, >, >=
6==, !=
