Logical Operators in Python

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Logical operators are used in “conditional” statements when we need more than one condition to be met.

• and     – checks whether two or more conditions are true
• or         – checks whether ‘at least’ one condition is true
• not      – check when a condition is not true

The ‘and’ logical operator is useful to find results within a particular range.

temp = 50

if temp > 19 and temp < 26:
    print("The temperature is very comfortable.")
elif temp < 0 or temp > 40:
    print("Stay indoors, it is a bad day outside")
else:
    print(f"{temp} degrees Celsius is uncomfortable.")

In the above example: if temp > 19 and temp < 26: the entire statement is only true when both conditions are met.  For:  elif temp < 0 or temp > 40: the entire statement is deemed true if either of the two conditions are true.

Exercise

Re-write this code asking the user to provide the temperature in Celsius.  Extend the conditional code to check whether the temperature is over 55^oC and state “humans can no longer dissipate heat beyond 55degC – find a cooler place!”

When using Boolean conditionals, we can drop the ‘== True’ part, it is assumed.

sunny = True

if sunny:   # <-- if sunny == True
    print("It is a sunny day.")
else:
    print("It is not a sunny day.")

We use the ‘not’ logical operator for Boolean conditionals, which flip True to False.

sunny = True

if not sunny:   # <-- if sunny == False // or // if sunny != True
    print("It is not a sunny day.")
else:
    print("It is a sunny day.")

Exercise: Extend this code to first ask the user for input:  “Is it a sunny day outside (Y/N)?”.  Convert their answer to a Boolean so that anything entered other than Y will return False.

Solution:

sunny = input("Is it sunny outside (Y/N)?: ")

if sunny == "Y":
    sunny = True
else:
    sunny = False

if sunny:   # <-- if sunny == True
    print("It is a sunny day.")
else:
    print("It is not a sunny day.")

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