Monday 18 November 2019

Back to Python

This post was for year 6 and 7 students taking a short Python class in late 2019.

(For more Python, see an earlier blog post.)
Dec 3rd 

For the last lesson of this short course, let's draw a Christmas tree!  Without any graphics, we might just use the '*' symbol.   For example:

# almost a Xmas tree!! 
height = 10
for wid in range(1,10):
    print((height-wid)*' '+wid*'*') 

gives .... 
a very simple Xmas Tree

Can you understand how this program works?  Can you improve this code?  eg a better shape, add a tree trunk,  add a snowman! or snow!!  There might be a prize for the best solution.

Nov 25th
After the class today, hopefully everybody can run the Python Editor/Compiler app on their Chromebook and save files to their Google Drive - let us know if you can not do this!

Today we discussed summing integers from 1 to N in a "for loop" and we also showed the Maths trick that gives the formula N*(N+1)/2 as the summation result.   Lastly we looked at the bottom right-hand example in my handout from last week, that finds factors of a number.   eg

# find the factors of a number
num = 12
for j in range(2, num-1):
    if int(num/j) * j == num:
    print j, ' is a factor of ', num

2 is a factor of 12
3 is a factor of 12
4 is a factor of 12
6 is a factor of 12

The key statement here is the test that divides two numbers, chops off any remainder from the division, and then multiplies by the second number (the divisor) to check if the result is equal to what we started with!   If you don't follow this, just try it out, eg 



int(12/5)*5 == 12

Now, instead of using the test "int(num/j) * j == num",  how about using Python's % (remainder) operator?   For example:


OK - so try to change the code so that it uses a remainder test to check if the second number is a factor of the first number.  You might also edit the code so that it will give an extra message when there are no factors (i.e. variable "num" is a prime).   We will look at this in the next lesson.

Nov 18th
After further investigation, it seems that the best approach with Chromebooks might be to use the Python Compiler Editor app (which should now be installed on your laptops).

This app should allow Python 2 code to be edited and saved on your Google drive.  Initially you might start with a very simple program stored on my drive at this location:

From the menu items at the bottom of the app screen, try to open the file listed above (copy and paste the long address), or you might start a new file and copy the code from below.)   Try running the code - does it work?  Do you understand how it works?  Make some changes (e.g. can you use a "for" or "while" loop to repeat the last 4 statements many times?

# maths drill
import random

n1 = random.randint(1,10)
n2 = random.randint(1,10)
prod = n1 * n2
print(str(n1)+" * "+str(n2)+" = "+str(prod))

Save the final program on your own Google drive, using the SaveAs button.  Hopefully this approach will let you edit, run and save Python programs!

If the above works, here's nice homework problem.  Please write a program to add up all the (whole) numbers from 1 to 100 and print the result.  We will discuss this next week.

Dr Bill

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