Mastering Python lesson3b_for_loops

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Mastering Programming in Python
Lesson 3(b)
All you need to know about FOR LOOPS

In this lesson you will …
 Learn about loops, specifically the FOR LOOP
 Predict the output (For Loop Task)
 Adapt and change code involving For Loops
 Compare ‘while’ and ‘for’ loops.
 Use the break statement and see how it works
 Learn about Nested Loops
 Learn about the need for initialisation (set starting value)
 Create your own For Loops
 Create the beginnings of an Arithmetic quiz using a
random function and for loops
 Big ideas: Is the universe digital? A program?
 Introducing Gottfried Leibniz and Konrad Zuse
*For this series we
assume students know
how to open, save and
run a python module.
Version: Python 3

• Introduction to the language, SEQUENCE variables, create a Chat bot
• Introduction SELECTION (if else statements)
• Introducing ITERATION (While loops)
• Introducing For Loops
• Use of Functions/Modular Programming
• Introducing Lists /Operations/List comprehension
• Use of Dictionaries
• String Manipulation
• File Handling – Reading and writing to CSV Files
• Importing and Exporting Files
• Transversing, Enumeration, Zip Merging
• Recursion
• Practical Programming
• Consolidation of all your skills – useful resources
• Includes Computer Science theory and Exciting themes for every
lesson including: Quantum Computing, History of Computing,
Future of storage, Brain Processing, and more …
Series Overview
*Please note that each lesson is not bound to a specific time (so it can be taken at your own pace)
Information/Theory/Discuss
Task (Code provided)
Challenge (DIY!)
Suggested Project/HW

Did you know?
Guido van Rossum, the guy on the right, created python!
He is a Dutch computer programmer and completed his
degree in the university of Amsterdam
He was employed by Google from 2005 until December
2012, where much of his time was spent developing the
Python language. In 2013, Van Rossum started working
for Dropbox.
Python is intended to be a highly readable language. It
has a relatively uncluttered visual layout, frequently using
English keywords where other languages use punctuation.
Guido van Rossum, the creator of Python
An important goal of the Python developers is making Python fun to use. This is
reflected in the origin of the name which comes from Monty Python

The difference between ‘While’ and ‘For’
For loops are traditionally used when you have a piece of code which you want
to repeat n number of times. As an alternative, there is the WhileLoop,
however, while is used when a condition is to be met, or if you want a piece of
code to repeat forever, for example -
For loops are used when the number of iterations are known before hand.
The name for-loop comes
from the English word
“for”, which is used as the
keyword in most
languages. The term in
English dates to ALGOL 58

For Loops and game design …
Take, for example, the game ‘Super Mario’. For
loops can be used to create a timed interval
recall loop for each animation. See if you can
spot the “for loop” in the code below.
It would be hard to come across a programmed game that has not utilised a
for loop of some kind in its code.

The anatomy of a For Loop
for <variable> in <sequence>:
<statements>
else:
<statements>
The For Loop can step through the items in any ordered
sequence list, i.e. string, lists, tuples, the keys of dictionaries
and other iterables. It starts with the keyword "for" followed
by an arbitrary variable name. This will hold the values of the
following sequence object, which is stepped through.
Generally, the syntax looks like this:

Task 1: Predict the output (using For Loops)
Predict the output, then code it yourself to see if you were right!
Both of these do the same thing. Note: 0 is the starting point.
Look out for FORMAT SPECIFIERS: The %d specifier refers specifically to a decimal (base 10) integer.
The %s specifier refers to a Python string.

Were your predictions right?Answers:
This is the Fibonacci sequence!

Nested Loops
And now for a Nested Loop. This will break each word into its constituent letters
and print them out.
A Nested loop is basically a loop within a loop. You can have a for loop inside a
while loop or vice versa. Let’s start with something simple. Use a for loop to print
out the items in a list.
OUTPUT
OUTPUT

#1 Predict the output: (Simple Loop)
x i Output
0 0
1 1
2 2
3
3
*View the slideshow if you want flying animations to help with clarity!
Start by listing your variables (in the order they come)

#2 Predict the output: (two ‘for’ loops!)
x i Output
0 0
1 1
2 2
3
j
0
1
2
4
5
6 6

#3 Predict the output: (Nested Loop!)
x i Output
0
j
*
*
Note the
indentation!
This second for
loop is nested
INSIDE the first
one!
0
1
2
1
2
3
0
1
2
0
1
2
0
1
2
4
5
6
7
8
9
10
11
12 12

Challenge 1: 3 and 4 times table up to 10
This bit of code produces the times tables for the numbers 1 and 2 (and only up
to 5). Can you change it to produce the following? (3 and 4 times table up to 10)
1. Type in the code below (nested loop used)
2. Run it to see what it does
3. Now try and change the values in the
program to get it to do what is required.
4. Once done, play around with these values
and get it to produce more timestables!
You could go all the way up to 100!
Desired output

Solution1: 3 and 4 times table up to 10
The key is to understand the way the “range” works in Python. Change the
numbers to the following and it should work! Now you can experiment with
doing more!
Output
Change the above to ….

The ‘Break’ statement – how it works!
found = False # initial assumption
for value in values_to_check() :
if is_what_im_looking_for(value) :
found = True
break
#end if
#end for
# ... found is True on success, False on
failure
Having no way out of a situation is never a good thing! In python programming,
you can use the ‘Break’ statement to exit a loop – say for instance the conditions
of the loop aren’t met.

Note how ‘break’ provides an early exit
Having no way out of a situation is never a good thing! In python programming, you can use
the ‘Break’ statement to exit a loop – say for instance the conditions of the loop aren’t met.
OUTPUT
Note only 1,2,3,4 are printed from the range and once x = 5, the loop is exited!
OUTPUT?
Nothing! This is because the
loop finds ‘1’ and breaks
before it can do anything!
???????

Challenge 2: Extend the code and get
someone to try out your program!
1. Copy the code on the right
and analyse how it works
(notice use of user input, lists
and for loops)
2. Extend the program to:
a) Ask the user how many more
holidays they are planning for
the coming year(s)
b) Allow them to enter the
places they would like to visit
c) Append these new values to
the list.
d) Print the new list.
e) If they enter a number over
10 or zero, exit the loop.
print ("**********Hello, welcome to the program***********")
print ("This program will ask you to enter the names of places you've been
to")
print ("Before we get started, please enter the number of places you want
to enter")
number = int(input("How many holidays have you had this year?: "))
print ("Thank you!")
print ("We'll now ask you to enter all the places you've traveled to: ")
places_traveled = [] #Empty list created to hold entered values
for i in range(number): #range(number) used because we want to limit
number of inputs to user choice
places = input("Enter Place:")
places_traveled.append(places)
print (("Here's a list of places you've been to: n"), places_traveled)

Task 2: Predict the output (using For Loops)
Predict the output, then code it yourself to see if you were right!
Counting by numbers other than 1 (hint: in this case 2)
Using incrementation (i+1) to achieve something …..
You can also COUNT DOWN (as opposed to counting up!)
Printing number out of a list is also a useful thing to do!

Were your predictions right?Answers:

Challenge 3:The beginnings of an Arithmetic
Quiz Program. Can you extend it?
1. Copy the code on the right
and analyse how it works
(notice use of random function
and for loops)
2. Extend the program to:
a) Create more questions (what
would you need to change to
do this?)
b) Add a division operator to the
mix so that the questions also
extend to division.
c) Gifted and Talented: What
else could you add to make
this program more interesting?
How about a score variable
that increments each time an
answer is correct?
#-------------------------------------------------------------------------------
# Name: Maths Quiz
# Purpose: Tutorial
# Author: teachingcomputing.com
# Created: 23/02/2016
# Copyright: (c) teachingcomputing.com 2016
#-------------------------------------------------------------------------------
import random
#identifying the variables we will be using
score=0
answer=0
operators=("x", "+", "-")
#Randomly generate the numbers and operators we will be using in this

Discussion: Is the universe Binary?
https://en.wikipedia.org/wiki/Digital_physics
You may find Wikipedia’s listing on digital universe possibilities an interesting read
In physics and
cosmology, digital
physics is a collection of
theoretical perspectives
based on the premise
that the universe is, at
heart, describable by
information and is
therefore computable.
Some scientists say that the universe may in fact be a computer program.

Initialisation: Variables must have starting values
Total = 0 (below) is setting the variable Total to zero at the start of the program!
The process of creating
a variable and giving it a
starting value is called
initialisation.
If ‘total’ didn’t have a
starting value, the
computer would throw
up an error later on! It is
also necessary to re-set
values at the start.
Above: allows for a running total of the numbers
entered by the user (new_number)

Useful Videos to watch on covered topics
https://youtu.be/atMuFCpxnUQ https://youtu.be/9LgyKiq_hU0
What is the nature of the universe we live in? Recommended video on Python For Loops

Suggested Project / HW / Research
 Create a research information point on Gottfried Leibniz
 Basic facts about him
 Achievements
 His interpretation and understanding of Binary
 How Binary plays a role in computers today!
 Write an essay (or create an informational power point) on ‘DO WE LIVE IN A
BINARY UNIVERSE?”
 What were Konrad Zuse’s views on a Binary/ digital universe
 Charles Babbage claimed that miracles were the ‘master programmer’ at work – do
you agree?
 If there is a God (higher power) might he be a programmer?
 What arguments (for and against) a Binary universe can you present?
Gottfried Leibniz Konrad Zuse

Useful links and additional reading
https://wiki.python.org/moin/ForLoop
http://www.tutorialspoint.com/python/python_for_loop.htm
http://www.learnpython.org/en/Loops
https://en.wikipedia.org/wiki/Konrad_Zuse
http://www.victorianweb.org/science/science_texts/bridgewater/intro.htm

Mastering Python lesson3b_for_loops

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