Unit 1Basic Python programs, functionsSpecial thanks to Roy McElmurry, John Kurkowski, Scott Shawcroft, Ryan Tucker, Paul Beck for their work.Except where otherwise noted, this work is licensed under:http://creativecommons.org/licenses/by-nc-sa/3.02Python!• Created in 1991 by Guido van Rossum (now at Google) Named for Monty Python• Useful as a scripting language script: A small program meant for one-time use Targeted towards small to medium sized projects• Used by: Google, Yahoo!, Youtube Many Linux distributions Games and apps (e.g. Eve Online)3Installing PythonWindows:• Download Python from http://www.python.org• Install Python.• Run Idle from the Start Menu.Mac OS X:• Python is already installed.• Open a terminal and run pythonor run Idle from Finder.Linux:• Chances are you already have Python installed. To check, run python from the terminal.• If not, install from your distribution's package system.Note: For step by step installation instructions, see the course web site.4Interpreted Languages• interpreted Not compiled like Java Code is written and then directly executed by an interpreter Type commands into interpreter and see immediate resultsComputerRuntimeEnvironmentCompilerCodeJava:ComputerInterpreterCodePython:5The Python Interpreter• Allows you to type commands one-at-a-time and see results• A great way to explore Python's syntax Repeat previous command: Alt+P6Our First Python Program• Python does not have a main method like Java The program's main code is just written directly in the file• Python statements do not end with semicolonshello.py1 print("Hello, world!")7The print Statementprint("text")print() (a blank line) Escape sequences such as \" are the same as in Java Strings can also start/end with 'swallows.py1234print("Hello, world!")print()print("Suppose two swallows \"carry\" it together.")print('African or "European" swallows?')8Comments• Syntax:# comment text (one line)swallows2.py123456# Suzy Student, CSE 142, Fall 2097# This program prints important messages.print("Hello, world!")print() # blank lineprint("Suppose two swallows \"carry\" it together.")print('African or "European" swallows?')9Functions• Function: Equivalent to a static method in Java.• Syntax:def name():statementstatement...statement Must be declared above the 'main' code Statements inside the function must be indentedhello2.py1234567# Prints a helpful message.def hello():print("Hello, world!")# main (calls hello twice)hello()hello()10Whitespace Significance• Python uses indentation to indicate blocks, instead of {} Makes the code simpler and more readable In Java, indenting is optional. In Python, you must indent.hello3.py12345678# Prints a helpful message.def hello():print("Hello, world!")print("How are you?")# main (calls hello twice)hello()hello()11Exercise• Rewrite the Figures lecture program in Python. Its output:______/ \/ \\ /\______/\ /\______/+--------+______/ \/ \| STOP |\ /\______/______/ \/ \+--------+12Exercise Solutiondef egg():top()bottom()print()def cup():bottom()line()print()def stop():top()print("| STOP |")bottom()print()def hat():top()line()print()def top():print(" ______")print(" / \\")print("/ \\")def bottom():print("\\ /")print(" \\______/")def line():print("+--------+")#
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