LESSON NOTE/GUIDE
PROGRAM
1 – PROCESS LIST CONTENTS - OUTPUT
· Create a list that contains words. Use a for loop to output each element one
word at a time.
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THE CODE
data = ["apple", "orange",
"pink", "carrot"]
for x in data:
print(x)
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EXPLANATION
The first line creates a list with
four strings in it.
The second line creates a loop. All lines indented under a for statement
are inside the loop. In this
program, the loop contains only the print statement.
This loop will be executed four
times with x taking on each value in the list.
The first time through, the value
of x will be “apple” and that is what will be outputted to screen.
The second time through the loop, x will get the value “orange” and that
will be outputted to screen.
The third and fourth times through,
the values “pink” and “carrot” will be outputted.
Note that in the loop above, x is
called the control variable.
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PROGRAM
2 – A SIMPLE LOOP
- Use a for
loop and the range(#,#) function to repeat a
statement five times.
- Explore by
changing the values 1 and 6 to other numbers to see what happens.
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THE CODE
for x in range(1,6):
print("hello")
print("done")
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EXPLANATION
The range(1,6)
function in the first line actually creates the sequence of numbers
[1,2,3,4,5]. It excludes the last
number so 6 is not in the sequence.
After the sequence is created, the
first line creates a for loop. The variable x is called the control variable as it controls the
loop. In each pass or iteration in the loop, the variable
x will take on one of the values in the sequence.
Note that the bottom print
statement is not indented so it is not inside the loop. It will therefore only be executed after
the loop is complete.
We will therefore print “hello” on
screen five times. Then the loop
will end.
After the loop is over, the final
print statement is executed and “done” is outputted to screen.
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PROGRAM
3 – OUTPUTTING THE CONTROL VARIABLE
- Output the
value of the control variable to screen.
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THE CODE
for x in range(1,6):
print("hi",
x)
print("done")
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EXPLANATION
This code will do the same as the
previous program but will also demonstrate how the control variable x
changes from one iteration to another.
Try it out.
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PROGRAM
4 – MORE ON THE range(#,#) FUNCTION
- Explore
with the range(#,#) function.
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THE CODE
# range function details
# arg1 - the lowest number in the list
# arg2 - the value at which the list stops before
# arg3 - the amount by which the list goes up (optional)
for x in range(2,9,2):
print(x)
print("done")
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EXPLANATION
Try changing the three arguments
inside the range(#,#,#) function to see what it
changes.
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PROGRAM
5 – OUTPUT ALL NUMBERS
- Use the range(#,#) function to output all numbers from 1 to
100 on the screen.
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THE CODE
# range function details
# arg1 - the lowest number in the list
# arg2 - the value at which the list stops before
# arg3 - the amount by which the list goes up (optional)
for x in range(1,101):
print(x)
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EXPLANATION
The program will output all numbers
from 1 to 100 on the screen.
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PROGRAM
6 – OUTPUT EVEN NUMBERS
- Write the
program that will output all even numbers between 1 and 100.
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THE CODE
for x in range(2,101,2):
print(x)
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EXPLANATION
The program will output all even
numbers from 2 to 100.
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PROGRAM
7 – OUTPUT BACKWARDS
- Write a
program that will output all numbers from 1 to 100 backwards, so from
100 down to 1. Remember that
lists can be reversed.
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THE CODE
for x in range(100,0,-1):
print(x)
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EXPLANATION
The program will output numbers 100
down to 1.
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THE
CODE (ALTERNATIVE APPROACH)
numbers = list(range(1,101))
numbers.reverse()
for x in numbers:
print(x)
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EXPLANATION
The first line of code uses the range(#,#) function to create a sequence of
numbers. The list function then
converts that sequence into a list.
That list is stored inside numbers.
The second line reverses the order
of elements in the numbers list.
The for loop then outputs all
elements of the list in order.
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PROGRAM
8 – LOOP OVER A STRING
- Write a
program that creates a string and loops over each character of that
string.
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THE CODE
word = "test"
for c in word:
print(c)
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EXPLANATION
In this case, the control variable c
(which is short for character) gets one letter at a time from the word
“test”. In the first iteration, c
will be “t”. In the second, it will
be “e”. In the third, it will be “s”
and in the final iteration it will be “t”.
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PROGRAM
9 – INTRODUCING NESTED LOOPS
- Part 1 -
Write a program that makes us of a for loop to output the word “three”
out three times to screen.
- Part 2 –
Place your program from Part 1 into another for loop. Make that loop repeat twice.
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THE CODE (PART 1)
for b in range(1,4):
print("three")
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EXPLANATION
The loop will repeat three times
and output “three” each time.
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THE CODE (PART 1)
for a in range(1,3):
for b in range(1,4):
print("three")
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EXPLANATION
When there is one loop inside
another, it is called nested loops.
The outer loop will loop
twice. In the first iteration of the
outer loop, the inner loop will output “three” 3 times.
In the second iteration of the
outer loop, the inner loop will again output “three” 3 times.
In total, the word “three” will be
outputted 6 times.
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PROGRAM
10 – NESTED LOOPS CONTROL VARIABLES
- Create a
program that will has two nested for loops and output their control
variable values to the screen.
- Analyze the
order of statements that get executed.
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THE CODE
for a in range(1,4): # a will get values 1, 2 & 3
for b in range(1,3): # b will get values 1 & 2
print(a, b)
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EXPLANATION
The above code will create the
following output:
1 1
1 2
2 1
2 2
3 1
3 2
The first line creates a for loop with the control variable a
set to take on values 1, 2 and 3.
Initially, it has the value 1.
The second line of code creates a
for loop with control variable b set to take on values 1 and 2. Initially, it has value 1.
The third line of code outputs the
values of a and b which are both one. So it outputs 1 1.
We are at the end of the inner loop
so we increment b by 1 to the value 2.
We repeat the print line and output 1 2.
We are at the end of the inner loop
and the control variable be has taken on all of its values so the inner
loop is done. Now we are at the end
of the outer loop. The value of
variable a is increased by 1 to the value 2. We now restart the inner loop with a equal to 2.
Initially, b will be one so the
program will output 2 1. Then, b
will be 2 and the program will output 2 2.
We are done with the inner loop and
therefore a is increased again to 3.
The inner is restarted again.
The print statement will get
executed twice, once outputting 3 1 and then 3 2.
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PROGRAM
11 – STAR PATTERN (TIME PERMITING)
- Create a
program that will output a square pattern of stars based on a user
inputted size.
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THE CODE
size = int(input("What size?"))
for r in range(0, size):
print ("*"
* size)
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EXPLANATION
There user will be asked This will
output a patter such as
***
***
***
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