Writing Perl Modules

Introducing reusable perl code using modules

Transcript

1. Perl Modules Monday, December 12, 2011
2. Agenda ✦ Writing Perl Modules ✦ Namespaces In Depth ✦ Using Perl Modules ✦ CPAN Monday, December 12, 2011
3. Writing Modules Photo Editing Program Monday, December 12, 2011
4. Writing Modules Photo Editing Program XML Parser Monday, December 12, 2011
5. Writing Modules Photo Editing Program XML Parser Pet Encyclopedia http://www.everystockphoto.com/photo.php?imageId=4319409 http://www.flickr.com/photos/psd/1005276581/ http://morguefile.com/archive/display/611435 Monday, December 12, 2011
6. Photo Editing Program XML Parser Pet Encyclopedia They All Maintain A Log File Monday, December 12, 2011
7. Modules ✦ Allow us to write log handling functionality once ✦ Use for every app ✦ No need to copy-paste Monday, December 12, 2011
8. Hello Module #!/usr/bin/perl use strict; use warnings; print "Hello Modules\n"; 1; #!/usr/bin/perl use strict; use warnings; use Hello; Hello.pm hello.pl Monday, December 12, 2011
9. The Rules ✦ Name the file .pm ✦ Have the last statement evaluate to true ✦ Put the file somewhere perl will find it #!/usr/bin/perl use strict; use warnings; print "Hello Modules\n"; 1; Monday, December 12, 2011
10. Is That All ? ✦ A module file is actually just perl code ✦ It is included in the app by a “use” directive ✦ The module is loaded and executed before anything else happens (at compilation) Monday, December 12, 2011
11. Playing Friendly ✦ When writing modules, we need to think how the module affect other modules and programs Monday, December 12, 2011
12. Plant Vs. Aliens sub secret_weapon { print("Aliens win\n") } sub hit_plants { secret_weapon(); } 1; sub secret_weapon { print("Plants Win\n") } sub hit_aliens { secret_weapon(); } 1; use Plants; use Aliens; print "Hitting the aliens\n"; hit_aliens(); Monday, December 12, 2011
13. Namespace ✦ As a program grows, it’s hard to keep track of all names of all the functions ✦ Using a namespace will prevent confusion Monday, December 12, 2011
14. The package keyword ✦ The keyword ‘package’ declares a namespace ✦ It is a lexical definition, valid until the end of scope ✦ All global subroutines and our variables are actually packaged scope package Aliens; use strict; sub secret_weapon { print("Aliens win\n") } sub hit_plants { secret_weapon(); } 1; Monday, December 12, 2011
15. Using The Packaged ✦ When using code from another package, we need to prefix it with the package name. ✦ The default package is called main use strict; use warnings; use AliensPkg; Aliens::hit_plants(); Monday, December 12, 2011
16. Module Template ✦ package name at the top ✦ Capital first letter ✦ Usually the same as the name of the file ✦ Ends with true value package ModuleName; use strict; use warnings; # Subroutines declarations go here 1; Monday, December 12, 2011
17. Q & A ✦ http://www.flickr.com/photos/92163630@N00/95509221/ Monday, December 12, 2011
18. Documentation ✦ Module documentation in perl is written in pod (Plain old documentation) ✦ Write documentation at the end of your sources ✦ Use perldoc to read the documentation Monday, December 12, 2011
19. pod rules Monday, December 12, 2011
20. POD Rules ✦ A pod command starts with an equal sign ✦ A command can take arguments in the same line ✦ A blank line must follow a command Monday, December 12, 2011
21. POD Example ✦ A =head1 command sets a title ✦ Normal text can appear anywhere in the pod ✦ All pod is written after the 1; (end of the module) ✦ Full code: Calc.pm 1; =head1 Simple Calculator Module The calculator module provides functionality related to calculating and doing math. It supports all basic operations. Monday, December 12, 2011
22. POD Commands ✦ =head1, =head2, =head3, =head4: title ✦ =over, =item, =back: list ✦ A line that starts with spaces will be indented - use for SYNOPSIS section Monday, December 12, 2011
23. POD Common Sections ✦ Name ✦ Synopsis ✦ Description ✦ See Also ✦ Bugs Monday, December 12, 2011
24. Refined Template package ModuleName; use strict; use warnings; 1; =head1 NAME ModuleName is a cool module to do the job =head1 DESCRIPTION =over =item func1(x, y) =item func2(x, y, z) =back =head1 SEE ALSO =head1 BUGS Monday, December 12, 2011
25. Q & A Monday, December 12, 2011
26. Perl Variable Types ✦ Use our keyword to denote a packaged variable ✦ Every subroutine is “our” ✦ Use my keyword for lexicals (they are not stored in the symbol table) Monday, December 12, 2011
27. my variables ✦ exists only in the scope they were declared in ✦ Scopes: block, eval, file use strict; use warnings; foreach my $number (1..10) { # OK print $number, "\n" } # Error print $number Monday, December 12, 2011
28. our variables ✦ Defined and stored within a packge ✦ accessed from everywhere in the program ✦ Not very useful, but are the default if not using strict Monday, December 12, 2011
29. Pop Quiz ✦ What Is Printed ? use strict; use warnings; package Foo; my $x = 5; package main; print "x = $x\n"; Monday, December 12, 2011
30. Pop Quiz ✦ What Is Printed ? ✦ x = 5 ✦ X is lexical, package keyword affects package variables use strict; use warnings; package Foo; my $x = 5; package main; print "x = $x\n"; Monday, December 12, 2011
31. local variables ✦ Temporarily store the current value of a global var ✦ Restore old value when leaving scope ✦ Useful for superglobals Monday, December 12, 2011
32. Pop Quiz ✦ What happens here ? use strict; use warnings; my @l = (1, 2, 3); { local $"=")("; print "(@l)\n"; } print "(@l)\n"; Monday, December 12, 2011
33. Pop Quiz ✦ What happens here ? ✦ $” determines the delimiter that will be printed when writing an array inside quotes ✦ Setting it locally changes its value only inside the block use strict; use warnings; my @l = (1, 2, 3); { local $"=")("; print "(@l)\n"; } print "(@l)\n"; Monday, December 12, 2011
34. Namespaces ✦ A namespace in perl is a special kind of hash ✦ It is called after the package name. For instance, %main:: for main package ✦ The hash holds typeglobs Monday, December 12, 2011
35. Demo: Using Typeglobs Monday, December 12, 2011
36. Manipulating Typeglobs ✦ Since packages are just hash maps, it’s possible to set or remove global package names by changing a hash ✦ This can be used to create subroutines dynamically ✦ Demo Monday, December 12, 2011
37. Q & A Monday, December 12, 2011
38. Using Perl Modules ✦ Loading external files in perl can be performed using any of the 3 keywords: ✦ do ✦ require ✦ use Monday, December 12, 2011
39. do ✦ Load an external file ✦ Execute the file line-by-line ✦ Return the value of the last statement ✦ Used mainly for loading configuration files ✦ Demo Monday, December 12, 2011
40. require ✦ Built on top of use ✦ Adds: ✦ Not loading same file twice ✦ Search for the file in @INC Monday, December 12, 2011
41. use ✦ Built on top of require ✦ Adds: ✦ Compile time running Monday, December 12, 2011
42. do, require, use ✦ Use ‘do’ for configuration files, but always consider YAML instead ✦ Use ‘require’ for dynamic or conditioned loading ✦ Use ‘use’ for dependencies ✦ Most of the time, use use Monday, December 12, 2011
43. Using Modules ✦ @INC holds all the search paths for modules ✦ %INC holds all the loaded modules ✦ change value of @INC using: use lib <newdir> ✦ Can use PERL5LIB environment variable Monday, December 12, 2011
44. Exporting Subroutines ✦ The Exporter module makes life a little easier ✦ It allows exporting of functionality from one module to another ✦ Note: If using exporter, module name and file name must be the same Monday, December 12, 2011
45. Using Exporter ✦ use base ‘Exporter’ ✦ our @EXPORT = qw/.../; ✦ our @EXPORT_OK = qw/.../; Monday, December 12, 2011
46. Exporter Tags ✦ Use EXPORT_TAGS to export a group of subroutines as a tag ✦ %EXPORT_TAGS = (T1 => [qw/foo bar/]); ✦ On the app: use MyModule qw/:T1/; Monday, December 12, 2011
47. Demo ✦ Build a Stack Module ✦ Export subroutines: mypush, mypop ✦ Use pod for documentation Monday, December 12, 2011
48. Testing Modules ✦ http://www.flickr.com/photos/busyprinting/4671731838/ Monday, December 12, 2011
49. Test::More ✦ A Unit testing framework for perl ✦ Use ‘prove’ command line utility to run the tests and get a detailed report ✦ Easy to use Monday, December 12, 2011
50. Test::More use Test::More tests => 5; use Calc; is( Calc::plus (1, 1), 2, "one plus one"); is( Calc::minus(3, 2), 1, "positive minus"); is( Calc::minus(0, 2), -2, "negative minus"); ok( Calc::plus (2, 2) == 4, "ok positive plus"); ok( Calc::minus(3, 5) == -1, "ok negative minus"); perldoc Test::More for complete syntax Monday, December 12, 2011
51. Directory Structure Module Root lib t bin Source root folder pm files t files (unit tests) pl files (if your module creates an app) Monday, December 12, 2011
52. Q & A Monday, December 12, 2011
53. CPAN Perl Module Repository Monday, December 12, 2011
54. ✦ Comprehensive Perl Archive Network ✦ Contains over 20,000 software modules ✦ Available as a command line tool that installs the modules ✦ Module Search: search.metacpan.org Monday, December 12, 2011
55. CPAN Tools ✦ App::cpanminus (http://cpanmin.us) ✦ CPAN::Mini ✦ Pod::Cpandoc Monday, December 12, 2011
56. Recommended Modules ✦ local::lib ✦ Try::Tiny ✦ Template::Toolkit ✦ Spreadsheet::ParseExcel ✦ Spreadsheet::WriteExcel ✦ Config::Any http://www.freedigitalphotos.net/images/view_photog.php? photogid=809 Monday, December 12, 2011
57. local::lib ✦ Install modules without requiring root permissions ✦ Sets environment variables accordingly ✦ No need for root access to install modules Monday, December 12, 2011
58. Try::Tiny ✦ Simplifies exception handling using die/eval ✦ Use try...catch keywords ✦ Use $_ for the error use strict; use warnings; use Try::Tiny; try { die 'FileError'; } catch { warn 'file error' if /FileError/; } Monday, December 12, 2011
59. Template::Toolkit ✦ An all purpose template engine in perl ✦ Write template file that uses variables ✦ From perl, define the variables and render ✦ Docs: http://template-toolkit.org/ Monday, December 12, 2011
60. Config::Any ✦ Parse any type of configuration file ✦ Give back a hash of config options ✦ Supported formats: ini, JSON, YAML, XML ✦ Acts as a front end for dedicated config modules Monday, December 12, 2011
61. Q & A Monday, December 12, 2011
62. Thank You ✦ Ynon Perek ✦ ynonperek.com ✦ ynonperek@yahoo.com ✦ All rights reserved Monday, December 12, 2011