Iteration by Item (For Loops Continued)

Iteration by Item

Whenever we execute a loop we have gone through an iteration. We can "iterate" (or loop) through the elements within certain data types. We can loop through the following data types as they are a collection of elements.

• Strings (a collection of characters)
• Lists (a collection of elements)
• Tuples (a collection of elements)

To iterate through a collection means to look at all of the elements within the collection. We can do this using the syntax shown below.

myList = [1,4,6,"hi"]

for item in myList:
    print(item)

# This will print 
1
4
6
hi

The variable "item" will be changed to equal the next item in the list after every loop (or iteration).

Example

An example of when we may iterate by item is if we are checking to see if a certain item exists in a list.

myList = [1,4,6,"hi"]

for item in myList:
    if item == 6:
        print("I found 6 in the list")
    else:
        print("This is not 6")

We can do the same with strings or with tuples.

# This program counts how many "l"s appear in the string 
myString = "hello tim"

count = 0
for item in myString:
    if item == "l":
        count += 1

print("I found", count, '"l"s in the string')

# When looping through a string we will look at each letter
# Looping through a tuple works the same as a looping through list