Lesson 6 - Loops - Conditions

Python Loops
If you want to iterate through all the elements of a list or a dictionary, python lets you do this with  two primitive loop commands:

• while loops
• for loops

The while Loop

Within the while loop,  as long as a condition is true, the set of statements are executed

Example

Print x as long as count is less than 5:

count = 1
while count < 6:
  print(count)
  count += 1

The for Loop

A for loop is used for iterating over a sequence (i.e a list, a tuple, a dictionary, a set, or a string).

Example1: Print each fruit in a fruit list:
fruits = [“apple”, “banana”, “kiwi”]
for x in fruits:
  print(x)

Example2: Print all the keys in a dictionary:
report={“subject”:”Maths”, “grade”: “A”,”marks”:99}

Conditions –  If … Else

You would use several conditions in your programming. 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,  “else statement” by else keyword

Example:

a = 45
b = 33

if b > a:
  print(“b is greater than a”)
else
  print(“b is not greater than a”)

 elif  condition  (elseif)

Example:

a = 85
b = 63

if b > a:
  print(“b is greater than a”)
elif b==a:
  print(“b is equals to a”)
else
  print(“b is less than a”)

The break statement
With the break statement we can stop the loop even if the while condition is true

Example

Exit the loop when x is 3:

x = 1
while x < 5:
   print(x)
   if x == 3:
       break
   x += 1

The continue statement

This will print 1,2,4,5,6.  if the i == 3, the continue  of the loop will be invoked skipping the print of 3
i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)