If ... Else in Python

Python Conditions and If statements

Python supports the usual logical conditions from mathematics:

Equals: a == b

Not Equals: a != b

Less than: a < b

Less than or equal to: a <= b

Greater than: a > b

Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly in "if statements" and loops.

An "if statement" is written by using the "if" keyword.

If statement:

import time
a = 33
b = 200
while True:    
    if b > a:
        print("b is greater than a")
        time.sleep(1)

elif:

Example: The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".

import time
a = 33
b = 33
while True:
    if b > a:
        print("b is greater than a")
        time.sleep(1)
    elif a == b:
        print("a and b are equal")  
        time.sleep(1)

else:

The else keyword catches anything which isn't caught by the preceding conditions.

import time
a = 200
b = 33
while True:
    if b > a:
        print("b is greater than a")
        time.sleep(1)
    elif a == b:
        print("a and b are equal") 
        time.sleep(1) 
    else:
        print("a is greater than b")
        time.sleep(1)

In this example a is greater than b, so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that "a is greater than b".

You can also have an else without the elif:

import time
a = 200
b = 33
while True:
    if b > a:
        print("b is greater than a")
        time.sleep(1)
    else:
        print("b is not greater than a")  
        time.sleep(1)

And

The and keyword is a logical operator, and is used to combine conditional statements:

Example Test if a is greater than b, AND if c is greater than a:

import time
a = 200
b = 33
c = 500
while True:
    if a > b and c>a:
        print("Both conditions are True")
        time.sleep(1)

Or

The or keyword is a logical operator, and is used to combine conditional statements:

Example Test if a is greater than b, OR if a is greater than c:

import time
a = 200
b = 33
c = 500
while True:
    if a > b or a>c:
        print("At least one of the conditions is True")
        time.sleep(1)

Not

The not keyword is a logical operator, and is used to reverse the result of the conditional statement:

Example: Test if a is NOT greater than b:

import time
a = 33
b = 200

while True:
    if not a > b:
        print("a is NOT greater than b")
        time.sleep(1)

Nest if

You can have if statements inside if statements, this is called nested if statements.

import time
x=41

while True:
    if x >10:
        print("above 10,")
        time.sleep(1)
        if x > 20:
            print("and also above 20!")
        else:
            print("but not above 20.")

---

https://www.w3schools.com/python/python_conditions.asp

Now let's replace the x with real time values of the light sensor from CPX

import time
from adafruit_circuitplayground import cp


while True:
    x = cp.light
    print("Light:", cp.light)
    if x >10:
        print("above 10,")
        time.sleep(1)
        if x > 20:
            print("and also above 20!")
        else:
            print("but not above 20.")