Games Development 2 Further Python Integrating with C

1
Games Development 2Further Python / Integrating
with C

• CO3301
• Week 13

2
Contents

• Further Python Examples
• Strings
• Further Conditions
• Working with Lists
• Function Techniques
• Libraries
• Extending / Embedding Python
• Calling Python from C

3
Python Strings

• Wide range of string support
• Basic operations
• print 'Hello ' 'World' Hello World
• print "Spam "4 Spam Spam Spam Spam
• Strings cant be written to easy to get round
• str "Hello World"
• newstr 'M' str2 Mello World
• Example of other methods
• print len( "Piece of String" ) Output 15
• print "london".capitalize() Output London
• print "too times too".replace( "too", "two" )
• Output two times two
• folderlist "C\Work\Python".split("\\")
• folderlist "C", "Work", "Python

4
Further Conditions

• More Conditions
• Set membership
• primes 1,2,3,5,7,11,13,17,19,23,29
• if x in primes
• print "x is prime"
• if year not in range(2000, 2100, 4) 2000-gt2100
  step 4
• print "Not a leap year"
• String / List comparison
• "one" lt "two" true lexicographical comparison
• 1,2,3 lt 1,2,4 Compare elements
• 1,3 lt 1,2,3 Shorter list always less than

5
Working with Lists

• List operations
• Working with this list
• a 66.25, 333, 333, 1, 1234.5
• Counting instances of a value
• print a.count(333), a.count(66.25), a.count('x')
• Output 2 1 0
• Insertion (anywhere), appending (at the end)
• a.insert(2, -1) Location, value
• a.append(333)
• print a
• Output 66.25, 333, -1, 333, 1, 1234.5, 333

6
Working with Lists

• More list operations
• Working with this list
• a 66.25, 333, -1, 333, 1, 1234.5, 333
• Removal (by location)
• x a.pop() Remove last element
• y a.pop(2) Remove specific element
• print a, x, y
• Output 66.25, 333, 333, 1, 1234.5 333 -1
• Removal (by value)
• a.remove(333) Remove first instance of 333
• print a
• Output66.25, 333, 1, 1234.5

7
Working with Lists

• List reordering
• Working with this list
• a 66.25, 333, 1, 1234.5
• Reversal
• a.reverse()
• print a
• Output 1234.5, 1, 333, 66.25
• Sorting
• a.sort()
• print a
• Output1, 66.25, 333, 1234.5

8
Functional List Creation

• List creation using functions
• map applies function to list elts to create
  new list
• def square(x) return xx
• print map(square, range(1, 11))
• Output 1, 4, 9, 16, 25, 36, 49, 64, 81, 100
• filter uses boolean function to filter elts
  in a list
• def NotDiv3(x) return x 3 ! 0
• filter(f, range(1, 15))
• Output 1, 2, 4, 5, 7, 8, 10, 11, 13, 14
• List comprehension powerful list creation
• def square(x) return xx
• primes 1,2,3,5,7,11,13,17,19,23,29
• print square(x) for x in primes if x10 lt 5
• Output 1,4,9,121,169,529

9
Function Techniques

• More Function Techniques
• Argument passing by name
• def AddRecord( name, ID 0, job "Unemployed
  )
• ...
• AddRecord( "Bill", 5 ) Normal style
• AddRecord( job"Builder", name"Bob" ) By name
• Argument unpacking
• def VectorLength( x, y )
• ...
• vector (10, 15)
• print VectorLength( vector ) unpacks 1
  argument to 2
• Documentation first line can be string
  literal
• def Square(x)
• "Returns the square of the argument"
• return xx

10
Libraries

• Can import support libraries
• Mathematics as in C
• import math
• print math.cos( math.pi / 3 ) Output 0.5
• Random numbers
• import random
• print random.choice('apple', 'pear', 'banana')
• print random.random() random float 0-1
• print random.randrange(6) random integer from
  0-5
• 5 random samples from list, e.g. 30, 83, 16,
  4, 8
• print random.sample(range(100), 5)

11
Integrating Python C

• Must include the Python headers and libraries
• Initialise Python at program start-up
• Simple scripts can be run directly
• PyRun_SimpleString( "print 'Hello World'" )
• But no interaction between C code / data and
  script
• Scripts can be run from a file equally easily
• Again no interaction
• For scripts to be useful in a game, need to
• Pass parameters from C to scripts, e.g. entity
  UIDs
• Get return values back
• Call back to C from the script to access/update
  data

12
Integrating Python C

• Basic process is intricate
• Have Python open the script, and find function to
  call
• Convert parameters from C types to Python
  objects
• Call script function
• Convert return value back to a C type
• All Python variables are reference counted
• Increase count when we first get them
• Decrease when finished
• Needed for Pythons garbage collection

13
Integrating Python C

• We end up with Python function calls like
• result CallPythonFn( "ScriptName", "MyFn", 1
  )
• where 1 is a parameter passed to the Python
  function
• To allow Python to call back into C
• Define a set of functions that will become a
  Python import library
• Identify import library to Python at start-up
  time
• Each C function must convert parameters and
  return values as before
• C functions can then be used in Python
• import game
• def PickUpHealthPack()
• game.AdjustHP( 20 ) AdjustHP is a C fn