The following is part of a on-going collection of Jupyter notebooks. The goal being to have a library of notebooks as an introduction to Mathematics and technology. These were all created by Gavin Waters. If you use these notebooks, be nice and throw up a credit somewhere on your page.

if-then statement

This one the most common conditional statements in all of programing, it simply sets up a boolean test and then if it passes does something. The structure in python is very easy.

if boolean-test :

do this stuff
more stuff
even more stuff
last bit of stuff

after the stuff is done the program continues

if 4>=3 :
    print('yowzaa')

yowzaa

if 4<=3 :
    print('yowzaa')

if 3!= 4:
    print('Handy != not equal to')

Handy != not equal to

You can also attach an else condition to the if statement.

if 4>=3:
    print('blue')
else:
    print("red")

blue

if 4<=3:
    print('blue')
else:
    print("red")

red

There is also elif conditions that can placed in sequence, first the if then the next elif condition etc etc until some boolean condition becomes true then it exits the statement.

if 4<=3:
    print('blue')
elif 5<=3:
    print("red")
elif 3<=3:
    print("yellow")
elif 2<=3:
    print("black")
else:
    print('white')

yellow

if 4<=3:
    print('blue')
elif 5<=3:
    print("red")
elif 6<=3:
    print("yellow")
elif 2>=3:
    print("black")
else:
    print('white')

white

for loops

Neat little things used for repedative tasks. You should have a parameter that you are moving through a list that is set up.

Like the if statement in that you have the for then a boolean with " : "

for a in range(0,4):
    print(a)

0
1
2
3

for a in range(0,4):
    if a>=3:
        print(a)

3

while loops

Similar to the for loop.

a=0
while a<=4:
    print(a)
    a+=1 # do not forget to increment a, or it will forever print out a

0
1
2
3
4

a=0
while a<=7:
    if 6<=a:
        print('blue ' + str(a))
    elif 5<=a:
        print('red ' + str(a))
    elif 4<=a:
        print('yellow ' + str(a))
    elif 2>=a:
        print('black ' + str(a))
    else:
        print('white ' + str(a))
        
    a+=1    

black 0
black 1
black 2
white 3
yellow 4
red 5
blue 6
blue 7

a =0 

while a<=5:
    print('Before the increment:' + str(a))
    
    a+=1
    print('After increment : ' + str(a))

Before the increment:0
After increment : 1
Before the increment:1
After increment : 2
Before the increment:2
After increment : 3
Before the increment:3
After increment : 4
Before the increment:4
After increment : 5
Before the increment:5
After increment : 6

Notice that the full while statement is carried out and then the while conditional is checked.

The while condition is create for letting the computer do the work for you.

Consider the following example, $f(x)=x^2+6x-16=(x+8)(x-2)$. We know there is some roots somewhere between -20 and 20. Lets see if there is an integer root.

a=-20
rootfound = False
while rootfound==False:
    if a**2+6*a-16==0:
        print('This is a root: '+ str(a))
        rootfound==True
    a+=1
    if a>=20:
        break

This is a root: -8
This is a root: 2

Another thing it can do is allow you to manually input information

Lets assume that $f(x)=42x^2-17x-15$. Can we set up a script to guess where there root is?

while True:
    a=input("enter your guess? ")
    a=float(a)
    if (42*a*a-17*a-15)*(42*a*a-17*a-15)<=0.005:
        print('close enough!!!!')
        break
    elif 42*a*a-17*a-15>=0:
        print('positive')
    else:
        print('negative')

enter your guess? 20
positive
enter your guess? 0
negative
enter your guess? 10
positive
enter your guess? 5
positive
enter your guess? 2
positive
enter your guess? 1
positive
enter your guess? 0.5
negative
enter your guess? 0.7
negative
enter your guess? 0.9
positive
enter your guess? 0.8
negative
enter your guess? 0.830
negative
enter your guess? 0.84
positive
enter your guess? 0.835
positive
enter your guess? 0.8325
close enough!!!!