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Download some materials

• Use a browser to go the following URL and download the materials to your machine: http://bit.ly/2eia34u
• Copy the file to your home directory
  • Mac OS X, Linux: e.g. /home/user
  • Windows: e.g. C:\Users\user

Extract the materials

• Mac OS X or Linux: type in the following in a shell prompt:
  • cd /home/user (your home directory)
  • unzip COMP3207-materials.zip
  • cd code
• Windows: right click on the zip file, ‘Extract All…’, enter your home directory, then run a command prompt and type:
  • cd C:\Users\username (your home directory)
  • cd code

What we’ll cover

• Starting the interpreter
• Variables
• Lists
• Loops
• Processing data files
• Making choices
• Creating functions

Starting the Python Interpreter

• The interpreter provides an interactive environment to play with the language
• Mac/Linux: Open a terminal window and type python
• Windows: Open a command prompt and type python
• At the prompt type ‘hello world!’

Control Flow: Repeating actions with loops

• What a loop does?
• Writing loops to repeat simple calculations
  • Indexing/ Counting starts from 0
• Track changes to a loop variable as the loop runs
• Track changes to other variables as they are updated by a for loop

Why indentation?

• Studies show that’s what people actually pay attention to
  • Every textbook on C or Java has examples where indentation and bracing don’t match
• Doesn’t matter how much indentation you use, but the whole block must be consistent
  
• Python Style Guide (PEP 8) recommends 4 spaces
• And no tab characters

Lists in Python

• Lists as arrays
• Indexing
  • Indexing some single value or even a whole set of values from a given list.
  • Indexing for retrieving single elements works as usual in python and indexing by negative numbers starts counting from the end.
• Slicing
  • Subset of a list, called a Slice, by specifying two indices. The return value is a new list containing all the elements of the list, in order, starting with the first slice index, up to but not including the second slice index.
  • Difference between upper and lower bound is the number of values in the slice.

Indexing and Slicing a List Example

Indexing and Slicing a List Example

Indexing and Slicing a List Example

Indexing and Slicing a List Example

Using Python libraries

• This introduction to Python is built around an end to end scientific example: data analysis
• What is a library (module) and its usage
• Reading data from a file

NumPy Arrays

• NumPy arrays and operations on arrays of data

NumPy arrays: Indexing and Slicing

• Ways of selecting individual values and subsets of data
• One-dimensional arrays are simple; on the surface they act similarly to Python lists.

Indexing in a NumPy 2D array

• The indices are (row, column) instead of (column, row).
• Example Patient inflammation data who were given treatment for arthritis:
  • Rows: Hold information for a single patient
  • Columns: Represent successive days

Cont..

Data visualisation using libraries

The purpose of computing is insight, not numbers, Richard Hamming.

• Best way to develop insight is often to visualise data.
• Plotting data using matplotlib library

Control Flow: Making choices

• Write conditional statements including if, elif and else
• A few things to note about the syntax:
  • Each if/ else statement must close with a colon (:)
  • Code to be executed as part of any if/else statement must be indented by four spaces.
  • Although not explicitly required, every if statement must also include an else statement - it just makes for a better program.
• Evaluate expressions containing and and or

Creating Functions

• Defining a function, the parameters that it takes, return value
• Test and debug a function
• Scope of variables
• Set default values for function parameters
• Divide programs into small, single-purpose functions

Command-line Programs

• Using values of command-line arguments in a program
• Handling flags and files separately in a command-line program
• Reading data from standard input in a program

Wrap-up Challenge: Connecting the dots

Write a python script (function) for Fahrenheit to Celsius temperature conversion and stores the output in a file.

• Hint (Tools to be used):
  • Unix pipes and filters
  • Python functions
  • Command-line programs
  • Using Fahr_to_kelvin() and Kelvin_to_celsius() functions

Thank You!