C463_02_python Artificial Intelligence with Python

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1. C463 / B551C463 / B551
Artificial IntelligenceArtificial Intelligence
Dana VrajitoruDana Vrajitoru
PythonPython

2. Python IntroductionPython Introduction
An interpreted, compiled, and interactive, object-An interpreted, compiled, and interactive, object-
oriented, dynamic, imperative, and open source oriented, dynamic, imperative, and open source
programming language. programming language.
Created in early 90's by Guido von Rossum at Stichting Created in early 90's by Guido von Rossum at Stichting
Mathematisch Centrum in the Netherlands. Mathematisch Centrum in the Netherlands.
The name comes from the Monty Python and not from The name comes from the Monty Python and not from
the snake. the snake.
There is a big community of Python programmers, with There is a big community of Python programmers, with
conferences and magazines:conferences and magazines:
http://pycon.org/ http://pycon.org/
Web site: Web site: www.python.org. .

3. Features of PythonFeatures of Python
Interactive: one can launch a Python console and run Interactive: one can launch a Python console and run
instructions directly it. instructions directly it.
Portable: available on most existing systems. It only Portable: available on most existing systems. It only
requires a C compiler to be ported to any new platform. requires a C compiler to be ported to any new platform.
Structure: functions, classes, modules. Structure: functions, classes, modules.
It is easy to embed Python with
 C and C++.
It is easy to embed Python with
 C and C++.
The user can write their own code in C or C++ and The user can write their own code in C or C++ and
compile it as Python modules or functions. That makes compile it as Python modules or functions. That makes
Python extensible. Python extensible.
Usual applications: scripts including CGI scripts, GUIs, Usual applications: scripts including CGI scripts, GUIs,
scientific computing. scientific computing.
Many existing libraries for all sort of purposes.Many existing libraries for all sort of purposes.

4. Syntax RulesSyntax Rules
The syntax is designed to be simplified as compared to The syntax is designed to be simplified as compared to
other languages like C/C++.other languages like C/C++.
Every compound instruction ends with ":"Every compound instruction ends with ":"
There are no blocks of code; blocks are implicitly created There are no blocks of code; blocks are implicitly created
by indentation.by indentation.
Expressions: usual arithmetic operators, named logic Expressions: usual arithmetic operators, named logic
operators: and, or, not.operators: and, or, not.
Assignments use the = sign but they don't have to end Assignments use the = sign but they don't have to end
with ";"with ";"
Comments start with # as in shell scripting.Comments start with # as in shell scripting.
Variables are declared by assigning them a value and Variables are declared by assigning them a value and
they are local to the block where they appear first.they are local to the block where they appear first.

5. Control StructuresControl Structures
Conditional:Conditional:
ifif condition: condition:
instructions instructions
elifelif condition: #* condition: #*
instructions instructions
elseelse: # optional: # optional
instructions instructions
Loops:Loops:
whilewhile condition: condition:
 
   instructions
 
   instructions
elseelse:
  # optional
:
  # optional
 
   instructions
 
   instructions
forfor var var inin S:
       
S:
       
 
   instructions
 
   instructions
elseelse:
  # optional
:
  # optional
 
   instructions
 
   instructions
forfor i i inin range(n): range(n):
 
   instructions
 
   instructions

6. Built-in Data StructuresBuilt-in Data Structures
ListsLists: linked lists implementing the subscript : linked lists implementing the subscript
operator:operator:
x = [1,2,3]x = [1,2,3]
x.append(4)x.append(4)
print x[2] # result: 3 print x[2] # result: 3
TupplesTupples: constant kind of arrays: constant kind of arrays
x = (1,2,3)x = (1,2,3)
DictionariesDictionaries: association lists: association lists
x = {}x = {}
x["word"] = referencex["word"] = reference
for k in x.keys():for k in x.keys():
print x[k] print x[k]

7. Functions and ParametersFunctions and Parameters
Function definition:Function definition:
defdef function_name (par1, par2, ...): function_name (par1, par2, ...):
body of the function body of the function
It supports default values for parameters.It supports default values for parameters.
All parameters are value parameters.All parameters are value parameters.
Any variable storing a complex data structure Any variable storing a complex data structure
contains a reference to it. Any changes to the contains a reference to it. Any changes to the
content of such a data structure in the function content of such a data structure in the function
will affect the variable passed in the function will affect the variable passed in the function
call.call.
Assignments involving a complex data structure Assignments involving a complex data structure
don't make a copy of it.don't make a copy of it.

8. More Built-in FunctionsMore Built-in Functions
Function Function typetype: returns the type of an object.: returns the type of an object.
type(0)type(0) – returns <type ‘int’> – returns <type ‘int’>
Checking if something is an integer:Checking if something is an integer:
if type(x) == type(0): ...if type(x) == type(0): ...
Reading a value from the terminal: input()Reading a value from the terminal: input()
x = input()x = input()
Returning a value from a function:Returning a value from a function:
return Truereturn True
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9. Example of ConditionalExample of Conditional
def check_type(x):def check_type(x):
if type(x) == type(0):if type(x) == type(0):
print x, "is an integer"print x, "is an integer"
elif type(x) == type(1.0):elif type(x) == type(1.0):
print x, "is a float"print x, "is a float"
elif type(x) == type(""):elif type(x) == type(""):
print x, "is a string"print x, "is a string"
elif type(x) == type([]):elif type(x) == type([]):
print x, "is an array"print x, "is an array"
......
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10. Example of while/elseExample of while/else
def Euler(a, b):def Euler(a, b):
if b==0:if b==0:
return areturn a
r = a % br = a % b
while r:while r:
a = ba = b
b = rb = r
r = a % br = a % b
else:else:
print "a divisible by b"print "a divisible by b"
return breturn b
return rreturn r
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11. BooleansBooleans
Truth values: True and False.Truth values: True and False.
False is equivalent with 0, and empty list False is equivalent with 0, and empty list
[], an empty dictionary {}.[], an empty dictionary {}.
Anything else is equivalent to True.Anything else is equivalent to True.
Example:Example:
x = 0x = 0
if not x:if not x:
print “0 is False”print “0 is False”
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12. Default Values for ParametersDefault Values for Parameters
Default values:Default values:
def function (var1 = value, var2 = value, ...):def function (var1 = value, var2 = value, ...):
Just like in C++, all the parameters that have Just like in C++, all the parameters that have
default values must be grouped at the end.default values must be grouped at the end.
def GCD1(a=10, b=20): ...def GCD1(a=10, b=20): ...
GCD1() -> 10GCD1() -> 10
GCD1(125) -> 5GCD1(125) -> 5
GCD1(12, 39) -> 3GCD1(12, 39) -> 3
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13. Variables and ScopeVariables and Scope
Module: one python file.Module: one python file.
Global scope: exists in the module in which they Global scope: exists in the module in which they
are declared.are declared.
Local scope: local to the function inside which it Local scope: local to the function inside which it
is declared.is declared.
Global variables in a module can be accessed Global variables in a module can be accessed
from somewhere else using the notation from somewhere else using the notation
module.variable.module.variable.
Example: string.digits contains ‘0123456789’.Example: string.digits contains ‘0123456789’.
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14. Example ScopeExample Scope
def test_scope():def test_scope():
for i in range(4):for i in range(4):
for j in range (3):for j in range (3):
x = i*10+jx = i*10+j
if x>20:if x>20:
print x,print x,
print xprint x
test_scope()test_scope()
21 22 30 31 32 3221 22 30 31 32 32
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15. Try - ExceptTry - Except
Try: attempts to execute an instruction. Try: attempts to execute an instruction.
If the operation is successful, it moves on.If the operation is successful, it moves on.
If not, we have the option of doing something If not, we have the option of doing something
else with the instructionelse with the instruction
except:except:
Another option: Another option:
except error_type:except error_type:
which does something only for a particular type which does something only for a particular type
of exception.of exception.
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16. def scope1():def scope1():
y = 15y = 15
y = 20y = 20
def scope2():def scope2():
y = 25y = 25
def scope3():def scope3():
try:try:
print yprint y
except:except:
print "cannot access global y"print "cannot access global y"
print daysprint days
y = 25y = 25
print yprint y
days=["monday", "tuesday"]days=["monday", "tuesday"]
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