c463 / b551 artificial intelligence dana vrajitoru python

C463 / B551C463 / B551Artificial IntelligenceArtificial Intelligence

Dana VrajitoruDana Vrajitoru

PythonPython

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. .

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.

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.

Control StructuresControl Structures

Conditional:Conditional:ifif condition: condition: instructions instructionselifelif condition: #* condition: #* instructions instructionselseelse: # 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

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 arraysx = (1,2,3)x = (1,2,3)DictionariesDictionaries: association lists: association listsx = {}x = {}x["word"] = referencex["word"] = referencefor k in x.keys():for k in x.keys(): print x[k] print x[k]

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 functionIt 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.

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

Artificial Intelligence – D. VrajitoruArtificial Intelligence – D. Vrajitoru

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"

......


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 rArtificial Intelligence – D. VrajitoruArtificial Intelligence – D. Vrajitoru

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”


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


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’.


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()

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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.


def scope1():def scope1():

y = 15y = 15

y = 20y = 20


y = 25y = 25


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"]


c463 / b551 artificial intelligence dana vrajitoru python

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