PYTHON MASTERCLASS - SILVER <MT_name_here> CAS Master < _here>

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1 PYTHON MASTERCLASS - SILVER <MT_name_here> CAS Master < _here>

2 Why are you here? Overview Housekeeping Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback Looking to teach coding as part of Computing, (most probably GCSE) Some basic knowledge of coding in Python Better understanding of what the exam boards require pupils to know Session 2 of 3 on a functional introduction to coding and computational thinking in Python

3 Housekeeping Overview Housekeeping Introduction Session 1 Session 2 Session 3 Plenary Homework Registration Session 1: Looping using iteration Session 2: Lists and Arrays Session 3: Strings * Please take a break as required during practical activities Questions Feedback

4 Introduction Overview Housekeeping Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback Success Criteria: By the end of today you will be able to: Apply iteration constructs effectively to solve problems Use and manipulate strings and lists Plan and implement simple algorithms using these concepts in Python Recognise how this relates to sections of the GCSE assignments

5 Typical GCSE expectations For the OCR GCSE programming Non-examined assessment (parts tested in the exam): Identify and use variables, operators, inputs, outputs and assignments The three basic programming constructs: Sequence; Selection; Iteration Suitable loops including count and condition controlled loops Different types of data, including Boolean, string, integer and real Basic string manipulation Basic file handling operations Arrays (or equivalent) Functions/sub programs to create structured code

6 Typical GCSE expectations It s all about being able to think Computationally and solve problems

7 Session 1: Looping using iteration Overview Eat, sleep, rave, repeat - Beardyman Housekeeping Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback

8 Revision From the last course you should be already familiar with: Sequence Selection Flowcharts Pseudocode Refresh your memory at: community.computingatschool.org.uk/resources/4402 The next few slides are for revision only!

9 Sequence The starting point for all algorithms Series of instructions one after each other Pick up cup Drink coffee Put down

10 Selection Useful algorithms will need to react to conditions that occur Is mug empty? Drink coffee Nibble biscuit Put down

11 Iteration Repeat parts of an algorithm to approach the desired outcome Is there coffee in mug? Pick up mug Drink coffee Put down

12 Planning using flowcharts Graphical representation of algorithm sequence. Good flowchart design must: Begin and end with the same shape Connect all steps with a direction arrow Be evenly spaced Have clear and concise descriptions

13 Planning using pseudocode This is a list of instructions outlining the operation of an algorithm written so that a human can understand them Good pseudocode design must: Have line numbers Have clear descriptions without being too complex Be indented to show similar blocks of code List actions as capital letters

14 What next? Consider how sequence, selection and iteration control structures form part of algorithm designs (flowcharts and pseudocode) Produce code from these designs using Python Look at some problems that require us to think Computationally

15 Algorithms that use selection /iteration Programs needs to respond to events This involves conditional constructs or selection IF ELIF ELSE Programs often repeat themselves A loop or iteration can be programmed to run a given number of times (count-controlled) FOR Or a loop can continue until a certain finishing state has been achieved (condition-controlled) WHILE, REPEAT UNTIL (aka DO WHILE)

16 Count-controlled loops A loop that runs a specific number of times: FOR var=start num TO end num execute this statement END FOR FOR i = 1 TO 10 OUTPUT i NEXT i = 1 Is i <= 10? Yes Output i i = i + 1 No

17 Python FOR construct Again Python uses white space and indents to separate FOR statements into blocks:

18 Condition-controlled loops - WHILE Loop that runs until condition is met, (and may never run): WHILE condition is true execute this statement END WHILE WHILE x < 10 OUTPUT x x = x + 1 END WHILE Is x < 10? Yes Output x x = x + 1 No

19 Condition-controlled loops - REPEAT Loop that will run at least once: REPEAT execute this statement UNTIL condition is true REPEAT OUTPUT x x = x - 1 UNTIL x <= 0 Output x x = x - 1 Is x <= 0? No

20 Python WHILE construct Python uses white space and indents to separate WHILE statements into blocks:

21 Python REPEAT construct Python doesn t have a specific REPEAT construct so we have to adapt a WHILE loop:

22 Rote learning is useful Python isn t always the ideal solution, especially if you need to meet exam board specification criteria Teach pupils structures to use but make sure concepts are embedded Output x x = x - 1 Yes Is x <= 0? No

23 Your turn Some practical examples of conditional and iterative programs using Python

24 Gotchas Syntax Errors: capitalising variables inconsistently, e.g. Lives is not the same as lives Wrongly using capital letters for functions, e.g. print not Print Missing : or ) or Using instead of Indentation doesn t line up Saving.py extension when pupils have not done this, their code does not feature syntax colour coding

25 Your turn... Basic count controlled loop for i in range(start, one more than end): execute this code Use a basic count controlled loop to: Print the word Python exactly 10 times Print the numbers from 1 to 10, and then print Boom! Print out the times table (to 12) for a user specified number in the format: 8 x 1 = 8 8 x 2 = 16 etc. Do it in only three lines of code!

26 Your turn... Condition controlled loop while condition is True: execute this code Use a condition controlled loop to: Try to plan this task using pseudocode or a flowchart before you code it... Create a program that asks users to "guess how many sly foxes there are in the room (there are four). If the correct number is guessed the program stops, otherwise it continues forever. Modify the program to ask the user to specify the number of guesses allowed and stop the loop at the appropriate point

27 Your turn... Dice rolling Rolling the dice - try this: from random import randint n = randint(1,100) print (n) Write Python code that simulates rolling a die Try to plan this task using pseudocode or a flowchart before you code it... Extend the program so it asks the user if they want to roll the dice; while they say yes it should tell them the number they have rolled ( You have rolled a ) and then ask them again after each roll Add the ability to select how many sides the die should have before starting the rolling sequence (remember to update the randint function) Extension (or something to do when you get home!) Have a go at coding the examples from the worksheets.

28 Session 2: Lists and arrays Overview Housekeeping Introduction Session 1 The human animal differs from the lesser primates in his passion for lists. H. Allen Smith Session 2 Session 3 Plenary Homework Questions Feedback

29 Arrays A collection of data all stored under one common name The data types used in this structure have to be the same, eg. an array of integers

30 Lists A collection of data all stored under one common name Data types can be mixed and the structure is dynamic 1 3 two True

31 Pretend lists are arrays Initially, lists and arrays could be considered as the same and used interchangeably Lists (and arrays) have elements referenced by an index value: testscore = [0,0,0] testscore[0] = 23 testscore[2] = 65 testscore[1] = 43

32 Accessing lists Lists implement the standard sequence interface: n = len(l) # Number of elements item = L[index] # Read element L[index] = value # Change element seq = L[start:stop] # Sub-list lastval = L[-1] # Element at end

33 Looping through lists A common task is to loop over a lists to find or summarise the data within it There is a traditional approach to this using WHILE loops but many languages support the use of FOR loops FOR is more convenient, however, it requires the whole list to be processed You can break out of the loop but this is considered bad practice

34 A comparison The traditional approach A Pythonesque approach

35 Modifying lists Lists are dynamic so the structure can be adjusted Other common list operations include: L.append( new ) # Add to end L.pop(4) # Remove an element L.insert(3, new ) # Insert new

36 Your turn Christmas List Activity Write a program that keeps asking for Christmas presents until the word STOP is entered at which point it prints out the list of the presents you have entered, followed by how many presents were entered. Extras Sort the list into order Pick an item from the list at random Remove an item if they have been naughty Tells you if the item ipad is in the list

37 Session 3: Strings Overview Housekeeping Like a puppet on a striiiiiiiiing. Sandie Shaw Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback

38 Storing Characters The character data type (often called char) stores a single letter or number If you store a number it is treated as a character not as a numerical value Strings are usually formed as an array of char (not technically a native data type themselves)

39 Strings As they are arrays they can be accessed as such: mystring = Hello mystring[0] mystring[2] mystring[4] However, they are immutable which means you cannot change parts of them

40 Looping through strings When using strings, we often want to loop through them as we have seen with a list, perhaps to count how many letters occur The same comparisons between methods applies

41 A comparison The traditional approach A Pythonesque approach

42 Shortcuts String objects have methods and can use functions that provide useful, commonly-used results: Number of characters in string First position of the character a Count number of character a s Replace all a s with zz Split by character a into a list Extract 3 characters from left of string Extract 3 characters from right of string len(thestring) thestring.find( a ) thestring.count( a ) thestring.replace( a, zz ) thestring.split( a ) thestring[:3] thestring[-3:]

43 Your turn Task 1 Write some code that counts the number of occurrences of the lowercase letter a in a string inputted by the user. Task 2 Write some code that decides whether a string input by the user contains all numeric characters or not, and displays an appropriate message. NB there is a short cut for this, so search for it. Task 3 Write a program that takes in a word and says whether or not it is a palindrome. (A palindrome is a word that is the same backwards as forwards like noon and radar).

44 Plenary Overview Housekeeping Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback Apply iteration constructs effectively to solve problems Use and manipulate strings and lists Plan and implement simple algorithms using these concepts in Python Recognise how this relates to sections of the GCSE assignments

45 A453 old tasks problem There are both simple and complicated ways of solving this...

46 A453 Set of tasks 2 problem 3 Count controlled loops and strings?

47 Homework Overview Housekeeping Introduction Session 1 Complete the follow-up tasks and the extension work from session 1. Session 2 Session 3 Plenary Homework Questions Feedback If you don t practice you won t improve and your lessons will be more difficult!

48 Interactive websites for learning Python Computer Science Circles University of Waterloo, Canada How to think like a Computer Scientist - Interactive Edition Problem solving with Algorithms and Data Structures using Python Pygame a set of Python modules designed for writing games.

49 Python Session #3 - Gold at a school near you, soon! Check CAS Events page regularly Subroutines (procedures and functions) File handling Tackling complex problems and more problems to practise writing solutions

50 Questions Overview Housekeeping Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback

51 On-line Survey Overview Housekeeping <tbc> Introduction Session 1 Session 2 Session 3 Plenary Homework Questions Feedback