1. H3D API Training  Part 3.1: Python – Quick overview

2. Python  Python Design & Syntax  Python / H3D Interface  Python Modules

3. Python  Design ◦ Written in C ◦ Python language is Object Oriented ◦ Exception handling ◦ Uses modules to offer specific features / functionality ◦ Can be extended to support new types / modules written in C or C++ (e.g. H3D API’s basic types) ◦ Memory management and automatic garbage collection

4. Python - Scope  Python uses indentation to define scope  Note: tabs and spaces are not equivalient in determining scope in python - be careful of mixing tabs and spaces! ◦ if (x != 0): ◦ print x ◦ else: ◦ print “NONE”

5. Python - Modules  Python modules located via PYTHONPATH environment variable  Can import module, or import all symbols in a module into the current scope: ◦ import os ◦ from math import * ◦ from math import cos

6. Python - Maths  C-style  New line terminates a statement ◦ x = 3 ◦ y = 5 ◦ avg = (x + y) / 2 ◦ print avg  Use ‘\’ to join two or more lines into a single statment

7. Python - Maths  import math  a = float(1)  b = int(1.6)  c = math.floor(1.6)  d = math.sqrt(9)  e = math.sin(3.1415)  f = math.log10(5)

8. Python - Strings  Delimited by either single or double quotes ◦ x = “Hello World” ◦ y = ‘Hello World’ ◦ z = ‘”Yes,” he said.’ ◦ w = “\”Yes,\” he said.”  Can span multiple lines using ‘\’ ◦ hello = "This is a rather long string containing\n\ ◦ several lines of text just as you would do in C.\n\ ◦ Note that whitespace at the beginning of the line is\ ◦ significant.”

9. Python - Strings  Concatenation ◦ a = “Hello” ◦ b = “World” ◦ c = a + “ “ + b  Repetition ◦ a = “Hello!” ◦ print a*5

10. Python - Strings  Sub-strings ◦ word = “Hello” ◦ print word[4] ◦ o ◦ print word[0:2] ◦ He ◦ print word[2:] ◦ llo ◦ print word[:-1] ◦ Hell

11. Python - Lists  List Insertion ◦ a.append( 4 ) ◦ a.insert( 1, 5 ) ◦ print a.pop()

12. Python - Globals  Scope of variables in functions defined by first use ◦ First use an assignment, presumed local ◦ First use a reference, presumed global ◦ Can override with global operator ◦ X = “test” ◦ def foo(): ◦ global X ◦ X = “bar”

13. Python - If  Standard C style, if, else, elif  Condition can be any valid python expression that returns a value  Does not require parenthesis ◦ if x > 5: ◦ print “Large” ◦ elif x > 2: ◦ print “Medium” ◦ else: ◦ print “Small”

14. Python - For  Unlike C, set based ◦ iterate over strings, lists and tuples ◦ items = [ “A”, “B”, “C” ] ◦ for i in items: ◦ print i ◦ str = “Hello” ◦ for c in str: ◦ print c

15. Python - Exceptions  Similar to C++, try / except block ◦ def foo(): ◦ try: ◦ print bar ◦ except: ◦ print “No Bar” ◦ raise “Foo Failed”

16. Python - Functions  “def” to define functions, argument list, default values ◦ def foo( bar = 0 ): ◦ print bar ◦ foo( 1 ) ◦ foo()

17. Python - Classes  Similar to C++ ◦ Constructor, base class (multiple inheritance), static members, etc ◦ class Basic: ◦ def __init__( self, name ): ◦ self.name = name ◦ def getName( self ): ◦ print self.name ◦ x = Basic( “X” ) ◦ y = Basic( “y” ) ◦ x.getName()

18. Python - Classes  Inheritance ◦ class Special(Basic): ◦ def __init__( self, name ): ◦ Basic.__init__( self, name ) ◦ def getName( self ): ◦ print self.name ◦ x = Basic( “X” ) ◦ y = Special( “y” ) ◦ y.getName()

19. Python Modules  Overview of useful Python library modules ◦ String manipulation ◦ File I/O ◦ http / ftp retrieval ◦ OS operations

20. Python Modules - Math  sin(), cos(), tan(), acos(), etc  degrees( a ), radians( a )  floor( x )  fmod( x, y )  log( x, base )  pow( x, y )  constants: pi, e

21. Python Modules - String  atof(str[,base]), atoi(), atol()  find( str, sub )  split( str, c )  join( str, c )  replace( str, old, new )

22. Python Modules - re  Regular expression module ◦ String matching, basic parsing ◦ compile( re_str ) # compile a RE ◦ search( pattern, str ) ◦ split( pattern, str ) – re.compile("a").match("ba", 1) # succeeds re.compile("^a").search("ba", 1) # fails re.compile("^a").search(”\na", 1) # fails

23. Python Modules - File I/O  Builtin functions ◦ f = open( filename, “r” ) ◦ f.write( text ) ◦ text = f.read() ◦ f.close()  OS Module contains file / directory manipulation

24. Python Modules - OS  chdir( path )  listdir( path )  mkdir( path )  rename( src, dst )  os.path: ◦ isfile( f ) ◦ isdir( f ) ◦ join( path1, path2 )