Python Programming

Python and Regular Expression 

Introduction 

DDM 8.0 Advanced 

© 2008 Hewlett-Packard Development Company, L.P. 

The information contained herein is subject to change without notice. 

HP CONFIDENTIAL - ENABLEMENT ONLY, NOT FOR CUSTOMER USE.

ABOUT THIS CHAPTER 

Objectives 

After completing this chapter, you will be able to: 

Know what is Python/Jython 

Be familiar with some of the Python semantics used in 

UCMDB scripting 

Having a foundation in Python to modify a Discovery 

Script 

Understand and manipulate Regular Expression 

2 


Python and Jython 




ABOUT PYTHON AND JYTHON 

More about Python 

Once upon a time: 

Origin and philosophy 

• First released by Guido van Rossum in 1991 

• Philosophy: 

– An easy and intuitive language just as powerful as major 

competitors 

– General purpose very-high-level language 

– Open source, so anyone can contribute to its development 

– Code that is as understandable as plain English 

– Suitability for everyday tasks, allowing for short development 

times 

4 




Python features: 

Core syntax and semantics are minimalist 

Multi-paradigm programming language: 

• Traditional Procedural Style 

• Object oriented Style 

Fully dynamic type system 

Automatic memory management 

Production Implementations: 

• Python (aka CPython or Classic Python) 

• Jython (Java Virtual Machine compliant) 

5 




Community and Interesting links: 

Community: 

• Open, community-based development model managed by 

the non-profit Python Software Foundation 

• Various parts of the language have formal specifications 

and standards, however the language as a whole is not 

formally specified 

Links: 

• http://www.python.org 

• http://www.python.org/doc 

• http://en.wikibooks.org/wiki/Python_Programming 

6 


ABOUT PYTHON 

Recommended Books 

• Good Introductory Book 

• Syntax 

• Language Programming Ref 

• Another good intro book 

• Syntax, programming 

• Debugging 

• Good Reference Book 

• Programming Examples 

• Sample Code 

7 



What is Jython? 

Python vs. Jython: 

Standard is CPython implementation. 

Jython (formerly JPython), is an implementation of 

the Python written in Java, which offers extra features: 

• Based on Java 1.2 or better 

• Import and use any Java class 

• Includes almost all of the modules in the standard Python 

distribution . The DDM Jython is based on an earlier 

version of Python so some libraries may not work. 

• Can convert Python source code into Java bytecode, 

which can be fully utilized by a Java program 

Links: 

• http://www.jython.org 

8 


Installing standalone Jython 

• http://www.jython.org 

9 


Jython 

Language Basics 




Python Programming 

Basics 

Basic Syntax 

Python is Case Sensitive 

Do not mix tabs and spaces 

• In UCMDB, we use the tab or 4 spaces, but the latter is not recommended. 

Scope and namespace 

• Global 

• Local (Functions) 

Comments 

• # This symbol will comment the rest of line 

• """ This is a comment on many 

lines""" 

Print command 

11 



Basics 

Python programs are composed of logical lines of code 

each made up of one or more physical lines. 

•Physical lines may end with comments 

•Comments are designated by a # and go to the end of the physical line 

•A line with just whitespace is called blank line 

•The end of a physical line ends most statements 

•Not terminated with a delimiter 

•If a line has no comment and ends with a \ then it continues to the next line 

•An open parenthesis ( open braket [ or brace { can cause lines to span 

multiple physical lines as well 

•Block structures are expressed by indentation 

12 



Basics 

Tokens – A component in a logical line. 

Token types are 

• Identifiers 

• Keywords 

• Operators 

• Delimiters 

• Literals 

13 



Basics 

Identifiers – A name to identify a variable, function, class, 

module, or object. 

• Starts with a letter A to Z or a to z or underscore(_) 

• Can be followed by zero or more letters, underscores and 

digits (0-9) 

• Case sensitive 

• Punctuation characters not allowed (@$%^&*!) 

Examples: 

Abc 

This_is_a_class 

C 

b 

14 



Basics 

Keywords – Identifiers that are reserved for special 

syntactic use. In Python version 2.1 they are: 

and finally pass 

assert for print 

break from raise 

Class global return 

Continue if try 

Def import while 

Del in yield 

Elif 

Else 

Except 

Exec 

is 

lambda 

not 

or 

15 



Basics 

Operators – Non-alphanumeric characters that are 

used to perform operations. 

+ > 

* & >= 

/ | 

% ^ != 

** ~ == 

// < 

16 



Basics 

Delimiters – The following symbols and 

combinations are used in expressions, lists, 

dictionaries, statements and strings. 

( ) &= 

[ ] |= 

{ } ^= 

, : >>= 

. ‘


Basics 

Working with Strings 

Single quotes or double quotes 

>>> 'spam eggs' 

'spam eggs' 

>>> 'doesn\'t' 

"doesn't" 

>>> "doesn't" 

"doesn't" 

>>> '"Yes," he said.' 

'"Yes," he said.' 

>>> "\"Yes,\" he said." 

'"Yes," he said.' 

>>> '"Isn\'t," she said.' 

'"Isn\'t," she said.' 

18 



Basics 


Strip function 

19 



Basics 


Strings can be subscripted (indexed) 

• the first character of a string has subscript (index) 0 

20 



Basics 


Assigning to an indexed position 

• Assigning to an indexed position in the string results in an 

error 

>>> word[0] = 'x' 

Traceback (most recent call last): 

File "", line 1, in ? 

TypeError: object doesn't support item 

assignment 

Positions can be inferred 

21 



Basics 


Length of a String 

22 



Basics 

Working with Lists 

Compound data types 

>>> a = ['spam', 'eggs', 100, 1234] 

>>> a 

['spam', 'eggs', 100, 1234] 

23 



Basics 

Working with List 

List Indexes 

• list indices start at 0 

• lists can be sliced, concatenated and so on 

24 



Basics 


Assignment 

• Assignment to slices is also possible, and this can even change the size of 

the list or clear it entirely. In the example below list a[I : j] . When you 

slice the ith item is included but the jth item is excluded. 

25 



Basics 


Assignment (cont’d) 

• Examples 

26 



Basics 


Length of a list 

• The built-in function len() also applies to lists 

>>> len(a) 

8 

27 



Basics 


Nesting lists 

• It is possible to nest lists (lists inside of another list) 

>>> q = [2, 3] 

>>> p = [1, q, 4] 

>>> len(p) 

3 

>>> p[1] 

[2, 3] 

>>> p[1][0] 

2 

>>> p[1].append('xtra') # See section 5.1 

>>> p 

[1, [2, 3, 'xtra'], 4] 

>>> q 

[2, 3, 'xtra'] 

28 



Basics 

Control Flow syntax 

Operators 

Operator 

function 

< less than 

greater than 

>= greater than or equal to 

== equal 

!= not equal 

another way to say not equal 

29 



Basics 


If statement: 

>>> x = -6 

>>> if x > 0: 

... print "Positive“ 

... elif x == 0: 

... print "Zero“ 

... else: 

... print "Negative“ 

... 

'Negative' 

30 



Basics 


For statements: 

>>> # Measure some strings: 

... a = ['cat', 'window', 'defenestrate'] 

>>> for x in a: 

... print x, len(x) 

... 

cat 3 

window 6 

defenestrate 12 

31 



Basics 

Control Flows syntax 

While statements: 

>>> x = 5 

>>> while x > 0: 

… print x 

… x = x – 1 

… 

5 

4 

3 

2 

1 

32 



Less Basic 

33 

Range function 

Built-in function if you need to iterate over a sequence of numbers 

>>> range(10) 

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 

>>> range(3, 10, 3) 

[3, 6, 9] 

>>> range(-10, -100, -30) 

[-10, -40, -70] 

>>> a = ['Mary', 'had', 'a', 'little', 'lamb'] 

>>> for i in range(len(a)): 

... print i, a[i] 

... 

0 Mary 

1 had 

2 a 

3 little 

4 lamb 



Less Basic 

Defining Functions 

Example: 

def sum2numbers(nb1, nb2): 

sum = nb1+nb2 

return sum 

print "The sum of ", 3, " and ", 4, " is ", sum2numbers(3,4) 

The keyword def introduces a function definition 

Followed by the function name, the parenthesized list of formal 

parameters and end by a colon 

Body of the function starts at the next line, and must be indented 

(use tab) 

Can return or not return a value 

34 



Less Basic 

Defining Functions 

Default Argument Values: 

def func(argV = 3): 

print argV 

argV = 4 

func() 

Result: 

3 

def sum3numbers(nb1, nb2=2, nb3=3): 

sum = nb1+nb2+nb3 

return sum 

print sum3numbers(3,nb3=4) 

35 

Result: 

9 



Less Basic 

Error Handling/Catching Exceptions 

try, except: 

try: 

print 1/0 

except ZeroDivisionError: 

print "You can't divide by zero, you silly.“ 

Result: 

You can't divide by zero, you silly. 

All built-in Python exceptions: 

• http://www.python.org/doc/current/lib/module-exceptions.html 

36 



Less Basic 

Error Handling/Catching Exceptions 

What is mainly used in UCMDB: sys.exc_info() 

• Example: 

stacktrace = traceback.format_exception(sys.exc_info()[0], 

sys.exc_info()[1], sys.exc_info()[2]) 

• This function returns a tuple (type, value, traceback) of three values that 

give information about the exception that is currently being handled : 

– type gets the exception type of the exception being handled 

– value gets the exception parameter 

– traceback gets a traceback object which encapsulates the call stack at 

the point where the exception originally occurred. 

37 


Regular Expressions 






What is a Regular Expression? 

A string that is used to describe or match a set of strings, according to 

certain syntax rules. 

What can it be used for? Example: 

• Everyday, you are receiving a message (among others) from 

your application similar to this one: 

13/11/2007 08:01 Good morning Dr Jones. You have 3 

new messages. 

• How can we easily retrieve the number of messages for Dr 

Jones and the date and time, knowing that the date and time 

will change, that we might have other messages with a 

different name and that we are only retrieving the last 

message? 

39 



Basics 

Basic Concepts 

Alternation 

• A vertical bar separates alternatives. For example, gray|grey can match 

"gray" or "grey". 

Grouping 

• Parentheses are used to define the scope and precedence of the 

operators (among other uses). For example, gray|grey and gr(a|e)y are 

equivalent patterns which both describe the set of "gray" and "grey". 

Quantification 

• ? : zero or one. For example, colou?r matches both "color" and 

"colour". 

• * : zero or more. For example, ab*c matches "ac", "abc", "abbc", 

"abbbc", and so on. 

• + : one or more. For example, ab+c matches "abc", "abbc", "abbbc", 

and so on, but not "ac". 

40 



Basics 

Syntax (non-exhaustive) 

. : (Period) Any single character except newline. 

• a.c matches "abc", etc., but [a.c] matches only "a", ".", or "c" 

[ ] : A single character that is contained within the brackets 

• For example, [abc] matches "a", "b", or "c“ 

• [a-z] specifies a range which matches any lowercase letter from "a" to 

"z“ 

• can be mixed: [abcx-z] matches "a", "b", "c", "x", "y", and "z" 

[^ ] : A single character that is not contained within the brackets 

( ) : Defines a marked subexpression 

• The string matched within the parentheses can be recalled later 

{m,n} : Matches the preceding element at least m and not more than n 

times. 

• For example, a{3,5} matches only "aaa", "aaaa", and "aaaaa". 

41 



Basics 

Syntax (non-exhaustive) 

What would be matched with these? 

• .at 

• [hc]at 

• [^b]at 

Answer: 

• Any three-character string ending with "at", including "hat", 

"cat", and "bat". 

• "hat" and "cat". 

• All strings matched by .at except "bat". 

42 



Basics 

Syntax (non-exhaustive), useful ones: 

[A-Za-z0-9] : Alphanumeric characters 

[A-Za-z] : Alphabetic characters 

[A-Za-z]+ : A series of alphabetic characters 

[ \t] : Space and tab 

[0-9] or \d : Digits 

[!"#$%&'()*+,-./:;?@[\\\]_`{|}~] : Punctuation characters 

[ \t\r\n\v\f] : Whitespace characters 

43 



Debugging 

Python Gui debugger 

Kodos 

• Free 

• OpenSource 

• Works with Python 

• http://kodos.sourceforge.net/a 

bout.html 

44 


DEMO OF THE KODOS 

TOOL 




CHAPTER SUMMARY 

Summary 

Python/Jython is a user-friendly and intuitive language, 

however it requires a strict semantic 

Regular expressions are an important feature, used almost 

regularly in DDM scripting. 

46

Python Programming

Create successful ePaper yourself

Delete template?

Save as template?