Python Basics Tom LeFebvre

Sept , 2002Python Basics2 Python Language Very High-Level Language Scripting Language (no compiling) Simple syntax Easy to Learn/Use Slow execution

Sept , 2002Python Basics3 Indentation Python uses indentation to identify blocks of code Might be difficult to get used to Code is more readable

Sept , 2002Python Basics4 Code Comments Code comments are identified with the “#” symbol Example # Print the value print “The value is:”, value

Sept , 2002Python Basics5 Statements The “if” statement has the syntax: if condition1 : doSometing elif condition2: doSomethingDifferent elif condition3: doAnotherThing else: doSomethingElse

Sept , 2002Python Basics6 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

Sept , 2002Python Basics7 The def Statement The “def” statement starts a method. def myMethod: print “myMethod executing.”

Sept , 2002Python Basics8 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] = print myList [“hello”, 2, 20.48]

Sept , 2002Python Basics9 Data Structures - Tuples Tuple: an immutable (mixed) collection of objects cityInfo = (‘Boulder’, (40.0, )) cityName, location = cityInfo #copy out components print cityName Boulder print location (40.0, )

Sept , 2002Python Basics10 Data Structures - Dictionaries Dictionary: non-ordered collection referred to by a “key”. myDict = { ‘joe’ : (‘Joseph Smith’, ‘Private”, ), ‘sam’:(‘Samuel Jones’, ‘Sergeant”, ), ‘bob’:(‘Robert Doe’, ‘General’, ), } key : data

Sept , 2002Python Basics11 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

Sept , 2002Python Basics12 Modules Modules are a collection of Python methods You can access modules by using “import” import math print math.pi OR from math import * print pi

Sept , 2002Python Basics13 Classes Python is an Object-Oriented language Class: a collection of data and methods – Data - things – Methods - actions class MyClass: def DoSomething(): def printSomething():

Sept , 2002Python Basics14 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.

Sept , 2002Python Basics15 Where to use self. When calling method: When accessing data: When defining a new function: self.method() a = self.dataVariable a = self.dataVariable def myNewMethod(self, arg1, arg2):

Sept , 2002Python Basics16 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

Sept , 2002Python Basics17 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

Sept , 2002Python Basics18 Troubleshooting Use print statements Add code incrementally & test