DS basics functions.ppt
- 1. Unit 1 Basic Python programs, functions Special 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/3.0
- 2. 2 Python! • 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)
- 3. 3 Installing Python Windows: • 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 python or 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.
- 4. 4 Interpreted Languages • interpreted Not compiled like Java Code is written and then directly executed by an interpreter Type commands into interpreter and see immediate results Computer Runtime Environment Compiler Code Java: Computer Interpreter Code Python:
- 5. 5 The 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+P
- 6. 6 Our 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 semicolons hello.py 1 print("Hello, world!")
- 7. 7 The print Statement print("text") print() (a blank line) Escape sequences such as " are the same as in Java Strings can also start/end with ' swallows.py 1 2 3 4 print("Hello, world!") print() print("Suppose two swallows "carry" it together.") print('African or "European" swallows?')
- 8. 8 Comments • Syntax: # comment text (one line) swallows2.py 1 2 3 4 5 6 # Suzy Student, CSE 142, Fall 2097 # This program prints important messages. print("Hello, world!") print() # blank line print("Suppose two swallows "carry" it together.") print('African or "European" swallows?')
- 9. 9 Functions • Function: Equivalent to a static method in Java. • Syntax: def name(): statement statement ... statement Must be declared above the 'main' code Statements inside the function must be indented hello2.py 1 2 3 4 5 6 7 # Prints a helpful message. def hello(): print("Hello, world!") # main (calls hello twice) hello() hello()
- 10. 10 Whitespace 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.py 1 2 3 4 5 6 7 8 # Prints a helpful message. def hello(): print("Hello, world!") print("How are you?") # main (calls hello twice) hello() hello()
- 11. 11 Exercise • Rewrite the Figures lecture program in Python. Its output: ______ / / / ______/ / ______/ +--------+ ______ / / | STOP | / ______/ ______ / / +--------+
- 12. 12 Exercise Solution def 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("+--------+") # main egg() cup() stop() hat()