Python Basics

1. Python Basics Tom LeFebvre

2. Python Language • Very High-Level Language • Scripting Language (no compiling) • Simple syntax • Easy to Learn/Use • Slow execution Python Basics

3. Indentation • Python uses indentation to identify blocks of code • Might be difficult to get used to • Code is more readable Python Basics

4. Code Comments • Code comments are identified with the “#” symbol • Example # Print the value print “The value is:”, value Python Basics

5. Statements • The “if” statement has the syntax: if condition1 : doSometing elif condition2: doSomethingDifferent elif condition3: doAnotherThing else: doSomethingElse Python Basics

6. Statements (cont.) • The “for” loop has the syntax: • The range statement is very useful for iterator in list: doSomethingWithTheIterator range(0,10) is the same as [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] for i in range(10): print i Python Basics

7. The def Statement • The “def” statement starts a method. def myMethod: print “myMethod executing.” Python Basics

8. Data Structures - Lists • List: a (mixed) collection of objects • Lists are mutable • Lists may be nested: [ [1, 2, 3] , [ 6, 7 ]] myList = [“hello”, 2, 10.24] myList[2] = 20.48 print myList [“hello”, 2, 20.48] Python Basics

9. Data Structures - Tuples • Tuple: an immutable (mixed) collection of objects cityInfo = (‘Boulder’, (40.0, -105.0)) cityName, location = cityInfo #copy out components print cityName Boulder print location (40.0, -105.0) Python Basics

10. Data Structures - Dictionaries • Dictionary: non-ordered collection referred to by a “key”. key : data myDict = { ‘joe’ : (‘Joseph Smith’, ‘Private”, 5226677), ‘sam’:(‘Samuel Jones’, ‘Sergeant”, 5124989), ‘bob’:(‘Robert Doe’, ‘General’, 7689098), } Python Basics

11. Other Peoples’ Code • Much code has already been written that can greatly help you. • Two types of “outside” code: • Modules – loose collection of methods • Classes – tightly-coupled, coherent collection of data and methods Python Basics

12. Modules • Modules are a collection of Python methods • You can access modules by using “import” import math print math.pi --- 3.14159265358 OR from math import * print pi --- 3.14159265358 Python Basics

13. Classes • Python is an Object-Oriented language • Class: a collection of data and methods • Data - things • Methods - actions class MyClass: def DoSomething(): def printSomething(): Python Basics

14. Inheritance • Code can “inherit” from classes • myTool inherits from class SmartScript • myTool has access to the data and methods in SmartScript • To access data or methods in any class use: myTool(SmartScript.SmartScript): self. Python Basics

15. Where to use self. • When calling method: • When accessing data: • When defining a new function: self.method() a = self.dataVariable def myNewMethod(self, arg1, arg2): Python Basics

16. Good Programming Practices • Modularization • Break up code into smaller pieces each of which performs some small task • avoids long methods • improves readability • easier to understand/maintain • easier to find bugs Python Basics

17. Good Programming Practices • Documentation • Should be short • Include one sentence for each method • In-line documentation where necessary • Choose names well • For methods – use verbs • For data variables – use nouns Python Basics

18. Troubleshooting • Use print statements • Add code incrementally & test Python Basics