Loops and conditions

Loops provide the method of iteration while condition allows or blocks the code execution when specified condition is meet.

For llop and While Loop

To iterate over the List. Lets prin the items in the list

L =['apple','banana','kite','cellphone']
for item in L:
    print(item)

apple
banana
kite
cellphone

What is range?

range(5), range(1,100), sum(range(100))

(range(0, 5), range(1, 100), 4950)

To iterate with for loop and adding the iterating index (the value of 10*k) to a blank List L.

L = []
for k in range(10):
    L.append(10*k)
L

[0, 10, 20, 30, 40, 50, 60, 70, 80, 90]

To create a double loop also called nested for loop. Lets create double for loop with i and j with range 5 and also populate the dictionary with key as (i,j)and value as 10*i+j when i=j and 100*1+j when i!=j.

D = {}
for i in range(5):
    for j in range(5):
        if i == j :
            D.update({(i,j) : 10*i+j})
        elif i!= j:
            D.update({(i,j) : 100*i+j})

print(D)

{(0, 0): 0, (0, 1): 1, (0, 2): 2, (0, 3): 3, (0, 4): 4, (1, 0): 100, (1, 1): 11, (1, 2): 102, (1, 3): 103, (1, 4): 104, (2, 0): 200, (2, 1): 201, (2, 2): 22, (2, 3): 203, (2, 4): 204, (3, 0): 300, (3, 1): 301, (3, 2): 302, (3, 3): 33, (3, 4): 304, (4, 0): 400, (4, 1): 401, (4, 2): 402, (4, 3): 403, (4, 4): 44}

To iterate two elements from two seperate Lists. It is not like nested for loop.

for item,j,k in zip(['apple','banana','kite','cellphone','pen'],\
                    range(5),[12,45,45,67,34]):
    print(item,"|",j,"|",k)

apple | 0 | 12
banana | 1 | 45
kite | 2 | 45
cellphone | 3 | 67
pen | 4 | 34

To iterate and ennumerate both together.

for i,item in enumerate(['apple','banana','kite','cellphone']):
    print("The",i,"th element is: ", item)

The 0 th element is:  apple
The 1 th element is:  banana
The 2 th element is:  kite
The 3 th element is:  cellphone

To create a list with for loop

A = [10*k**2+5*k+1 for k in range(10)]
print(A)

[1, 16, 51, 106, 181, 276, 391, 526, 681, 856]

AA = [[10*x**2+5*y+1 for x in range(3)] for y in range(3)]
print(AA)

[[1, 11, 41], [6, 16, 46], [11, 21, 51]]

To iterate over List of List

for i in range(3): 
    for j in range(3):
        print("The","(",i,",",j,")","th element is: ",AA[i][j])

The ( 0 , 0 ) th element is:  1
The ( 0 , 1 ) th element is:  11
The ( 0 , 2 ) th element is:  41
The ( 1 , 0 ) th element is:  6
The ( 1 , 1 ) th element is:  16
The ( 1 , 2 ) th element is:  46
The ( 2 , 0 ) th element is:  11
The ( 2 , 1 ) th element is:  21
The ( 2 , 2 ) th element is:  51

To use while loop.

i = 0
while i <5:
    print( i, "th turn")
    i = i+1

0 th turn
1 th turn
2 th turn
3 th turn
4 th turn

To break for loop implementing if condition

for i in range(10):
    print(i)
    if i ==3:
        break

To test the if conditions:

import random as random

for i in range(10):
    r = random.uniform(1,10)
    if r<2 and r>0:
        print("It is samaller then 2 and greater then 1","|", r)
    elif r<4 and r>2:
        print("It is samaller then 4 and greater then 2","|", r)
    elif r<6 and r>4:
        print("It is samaller then 6 and greater then 4","|", r)
    elif r<8 and r>6:
        print("It is samaller then 8 and greater then 6","|", r)
    elif r<10 and r>8:
        print("It is samaller then 10 and greater then 8","|", r)

It is samaller then 10 and greater then 8 | 8.910435750481426
It is samaller then 8 and greater then 6 | 6.616669779231224
It is samaller then 4 and greater then 2 | 3.8009645328925896
It is samaller then 4 and greater then 2 | 3.3039198434839117
It is samaller then 4 and greater then 2 | 3.2192327041596696
It is samaller then 10 and greater then 8 | 8.658302824387317
It is samaller then 10 and greater then 8 | 9.048987906482312
It is samaller then 10 and greater then 8 | 8.061577985253708
It is samaller then 8 and greater then 6 | 6.301327115111054
It is samaller then 6 and greater then 4 | 5.316492901781898

To find sum from 0 to 1000

s = 0
for i in range(1000+1):
    s = s+i
s

To find sum from 0 to 1000 (only even)

s = 0
LE = []
for i in range(1001):
    if i%2 ==0:
        LE.append(i)
        s = s+i
s, sum(LE)

(250500, 250500)

References:

https://docs.python.org/3/tutorial/index.html