Download Python - Quick overview

H3D API Training
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Part 3.1: Python – Quick overview
Python
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Python Design & Syntax
Python / H3D Interface
Python Modules
Python
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Design
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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
Python - Scope
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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!
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if (x != 0):
print x
else:
print “NONE”
Python - Modules
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Python modules located via PYTHONPATH
environment variable
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Can import module, or import all symbols in a module
into the current scope:
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import os
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from math import *
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from math import cos
Python - Maths
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C-style
New line terminates a statement
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x = 3
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y = 5
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avg = (x + y) / 2
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print avg
Use ‘\’ to join two or more lines into a single statment
Python - Maths
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import math
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a = float(1)
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b = int(1.6)
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c = math.floor(1.6)
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d = math.sqrt(9)
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e = math.sin(3.1415)
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f = math.log10(5)
Python - Strings
Delimited by either single or double quotes
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x = “Hello World”
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y = ‘Hello World’
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z = ‘”Yes,” he said.’
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w = “\”Yes,\” he said.”
Can span multiple lines using ‘\’
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hello = "This is a rather long string containing\n\
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several lines of text just as you would do in C.\n\
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Note that whitespace at the beginning of the line is\
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significant.”
Python - Strings
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Concatenation
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a = “Hello”
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b = “World”
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c = a + “ “ + b
Repetition
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a = “Hello!”
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print a*5
Python - Strings
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Sub-strings
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word = “Hello”
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print word[4]
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o
print word[0:2]
He
print word[2:]
llo
print word[:-1]
Hell
Python - Lists
List Insertion
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a.append( 4 )
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a.insert( 1, 5 )
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print a.pop()
Python - Globals
Scope of variables in functions defined by first use
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First use an assignment, presumed local
First use a reference, presumed global
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Can override with global operator
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X = “test”
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def foo():
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global X
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X = “bar”
Python - If
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Standard C style, if, else, elif
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Condition can be any valid python expression that
returns a value
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Does not require parenthesis
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if x > 5:
print “Large”
elif x > 2:
print “Medium”
else:
print “Small”
Python - For
Unlike C, set based
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iterate over strings, lists and tuples
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items = [ “A”, “B”, “C” ]
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for i in items:
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print i
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str = “Hello”
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for c in str:
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print c
Python - Exceptions
Similar to C++, try / except block
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def foo():
try:
print bar
except:
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print “No Bar”
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raise “Foo Failed”
Python - Functions
“def” to define functions, argument list, default values
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def foo( bar = 0 ):
print bar
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foo( 1 )
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foo()
Python - Classes
Similar to C++
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Constructor, base class (multiple inheritance), static
members, etc
class Basic:
def __init__( self, name ):
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self.name = name
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def getName( self ):
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print self.name
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x = Basic( “X” )
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y = Basic( “y” )
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x.getName()
Python - Classes
Inheritance
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class Special(Basic):
def __init__( self, name ):
Basic.__init__( self, name )
def getName( self ):
print self.name
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x = Basic( “X” )
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y = Special( “y” )
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y.getName()
Python Modules
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Overview of useful Python library modules
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String manipulation
File I/O
http / ftp retrieval
OS operations
Python Modules - Math
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sin(), cos(), tan(), acos(), etc
degrees( a ), radians( a )
floor( x )
fmod( x, y )
log( x, base )
pow( x, y )
constants: pi, e
Python Modules - String
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atof(str[,base]), atoi(), atol()
find( str, sub )
split( str, c )
join( str, c )
replace( str, old, new )
Python Modules - re
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Regular expression module
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String matching, basic parsing
compile( re_str ) # compile a RE
search( pattern, str )
split( pattern, str )
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re.compile("a").match("ba", 1)
# succeeds
re.compile("^a").search("ba", 1)
# fails
re.compile("^a").search(”\na", 1) # fails
Python Modules - File I/O
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Builtin functions
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f = open( filename, “r” )
f.write( text )
text = f.read()
f.close()
OS Module contains file / directory manipulation
Python Modules - OS
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chdir( path )
listdir( path )
mkdir( path )
rename( src, dst )
os.path:
◦ isfile( f )
◦ isdir( f )
◦ join( path1, path2 )