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H3D API Training

H3D API Training. Part 3.1: Python – Quick overview. Python. Python Design & Syntax Python / H3D Interface Python Modules. Python. Design Written in C Python language is Object Oriented Exception handling Uses modules to offer specific features / functionality

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H3D API Training

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  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) # succeedsre.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 )

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