C463_02_python.ppt,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

C463 / B551
C463 / B551
Artificial Intelligence
Artificial Intelligence
Dana Vrajitoru
Dana Vrajitoru
Python
Python

Python Introduction
Python 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 Python
Features 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 Rules
Syntax 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 Structures
Control Structures
Conditional:
Conditional:
if
if condition:
condition:
instructions
instructions
elif
elif condition: #*
condition: #*
instructions
instructions
else
else: # optional
: # optional
instructions
instructions
Loops:
Loops:
while
while condition:
condition:
instructions
instructions
else
else: # optional
: # optional
instructions
instructions
for
for var
var in
in S:
S:
instructions
instructions
else
else: # optional
: # optional
instructions
instructions
for
for i
i in
in range(n):
range(n):
instructions
instructions

Built-in Data Structures
Built-in Data Structures
Lists
Lists: 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
Tupples
Tupples: constant kind of arrays
: constant kind of arrays
x = (1,2,3)
x = (1,2,3)
Dictionaries
Dictionaries: association lists
: association lists
x = {}
x = {}
x["word"] = reference
x["word"] = reference
for k in x.keys():
for k in x.keys():
print x[k]
print x[k]

Functions and Parameters
Functions and Parameters
Function definition:
Function definition:
def
def 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.

More Built-in Functions
More Built-in Functions
Function
Function type
type: 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 True
return True
Artificial Intelligence – D. Vrajitoru

Example of Conditional
Example 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/else
Example of while/else
def Euler(a, b):
def Euler(a, b):
if b==0:
if b==0:
return a
return a
r = a % b
r = a % b
while r:
while r:
a = b
a = b
b = r
b = r
r = a % b
r = a % b
else:
else:
print "a divisible by b"
print "a divisible by b"
return b
return b
return r
return r

Booleans
Booleans
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 = 0
x = 0
if not x:
if not x:
print “0 is False”
print “0 is False”

Default Values for Parameters
Default 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() -> 10
GCD1() -> 10
GCD1(125) -> 5
GCD1(125) -> 5
GCD1(12, 39) -> 3
GCD1(12, 39) -> 3

Variables and Scope
Variables 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 Scope
Example 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+j
x = i*10+j
if x>20:
if x>20:
print x,
print x,
print x
print x
test_scope()
test_scope()
21 22 30 31 32 32
21 22 30 31 32 32

Try - Except
Try - 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 instruction
else 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 = 15
y = 15
y = 20
y = 20
def scope2():
def scope2():
y = 25
y = 25
def scope3():
def scope3():
try:
try:
print y
print y
except:
except:
print "cannot access global y"
print "cannot access global y"
print days
print days
y = 25
y = 25
print y
print y
days=["monday", "tuesday"]
days=["monday", "tuesday"]

C463_02_python.ppt,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

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