3.1.1.14 SECTION SUMMARY (1/2)

Key takeaways

1. The comparison (or the so-called relational) operators are used to compare values. The table below illustrates how the comparison operators work, assuming that x = 0, y = 1, and z = 0:

Operator	Description	Example
==	returns if operands' values are equal, and False otherwise	x == y # False x == z # True
!=	returns True if operands' values are not equal, and Falseotherwise	x != y # True x != z # False
>	True if the left operand's value is greater than the right operand's value, and False otherwise	x > y # False y > z # True
<	True if the left operand's value is less than the right operand's value, and False otherwise	x < y # True y < z # False
≥	True if the left operand's value is greater than or equal to the right operand's value, and Falseotherwise	x >= y # False x >= z # True y >= z # True
≤	True if the left operand's value is less than or equal to the right operand's value, and Falseotherwise	x <= y # True x <= z # True y <= z # False

2. When you want to execute some code only if a certain condition is met, you can use a conditional statement:

• a single if statement, e.g.:

x = 10 if x == 10: # condition print("x is equal to 10") # executed if the condition is True

• a series of if statements, e.g.:

x = 10 if x > 5: # condition one print("x is greater than 5") # executed if condition one is True if x < 10: # condition two print("x is less than 10") # executed if condition two is True if x == 10: # condition three print("x is equal to 10") # executed if condition three is True

Each if statement is tested separately.

• an if-else statement, e.g.:

x = 10 if x < 10: # condition print("x is less than 10") # executed if the condition is True else: print("x is greater than or equal to 10") # executed if the condition is False

• a series of if statements followed by an else, e.g.:

x = 10 if x > 5: # True print("x > 5") if x > 8: # True print("x > 8") if x > 10: # False print("x > 10") else: print("else will be executed")

Each if is tested separately. The body of else is executed if the last if is False.
• The if-elif-else statement, e.g.:

x = 10 if x == 10: # True print("x == 10") if x > 15: # False print("x > 15") elif x > 10: # False print("x > 10") elif x > 5: # True print("x > 5") else: print("else will not be executed")

If the condition for if is False, the program checks the conditions of the subsequent elif blocks - the first elif block that is True is executed. If all the conditions are False, the else block will be executed.
• Nested conditional statements, e.g.:

x = 10 if x > 5: # True if x == 6: # False print("nested: x == 6") elif x == 10: # True print("nested: x == 10") else: print("nested: else") else: print("else")