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Archive:Python/Operators

2008-08-25T15:39:39Z

85.250.242.189: /* Slicing */ reversing

=Operations, The Format Specifier, and Other Commands=

==Operations==

There are certain things that you can do with all of the ''types''. You can ''do simple math, index, slice, and check for membership.'' You can also use the Format Specifier in ''strings''.

===Simple Math===

Math is very straight forward in Python. + adds, - subtracts, / divides, and believe it or not * multiplies. The main thing to comment on is %. % divides a problem and then returns the remainder. This is called the modulo operation.

Type:

>>> '''9 % 3'''

0

Now Type:

>>> '''9 % 2'''

1

The % command can be used to find out if something is even or odd or if it is a multiple of some number. Here is some code that is a little advanced for you right now. Just type it in and now that within a couple of lessons you will know what you did. When you type '''"print a is even"''' it must be 4 spaces to the right of the '''i''' in '''if''', I am having trouble working with Wikiversity and can't get it to do that on this page without forming some kind of box.

Type:

>>> '''a = 4'''
>>> '''if a % 2 == 0:'''
... '''print "a is even"'''
'''a is even'''

You can also use variables, and elements and values in simple math.

Type:

>>> '''x = 1'''

>>> '''y = 5'''

Now Type:

>>> '''x + y'''

'''6'''

That is how the variable works.

Type:

>>> '''x = [1, 2, 3]'''

Now Type:

>>> '''x[1] + x[2]'''

'''5'''

That is how you use elements from a tuple or list to do math.

Type:

>>> '''x = {'a':1, 'b':2}'''
=You can also add and multiply strings, tuples, and lists.
Now Type:

>>> '''x['a'] + x['b']

'''3'''

That is how you do math with values from a dictionary. Don't forget to use quotations around the keys unless you use ''integers'' as the keys. Spend a couple of minutes messing around with this stuff, its fun and it'll help you remember it better. You may also add strings, tuples, and lists.

====Concatenating====

To add two strings together. to do this you just type the first string, an addition sign, the second string.

Type:

>>> '''"Python" + " is awesome"'''

You can do the same with variables refering to strings.

Type:

>>> '''x = "Python"'''

>>> '''y = " is awesome"'''

Now Type:

>>> '''x + y'''

''''Python is awesome''''

You can do the same with tuples.

Type:

>>> '''x = ('I', 'Love')

>>> '''y = ('Wikiversity',)''' ''DON'T FORGET THE COMMA AFTER '''WIKIVERSITY'''''

Now Type:

>>> '''print x + y'''

'''('I', 'Love', 'Wikiversity')'''

It works the same with ''lists''. What you cannot do is combine two different kinds of ''types''.

Type:

>>> '''x = ('I', 'Love')'''

>>> '''y = 'Python''''

Now Type:

>>> '''print x + y'''

'''Traceback (most recent call last):'''

'''File "<pyshell#91>", line 1, in ?'''

'''print x + y'''

'''TypeError: can only concatenate tuple (not "str") to tuple'''

====Multiplying ''Types''====

Multiplying is very easy and straight forward.

Type:

>>> '''x = 'dog''''

Now type:

>>> '''x * 5'''

''''dogdogdogdogdog''''

Now with a tuple.

Type:

>>> '''x = ('dog',)'''

Now Type:

>>> '''x * 5'''

'''('dog', 'dog', 'dog', 'dog', 'dog')'''

Now with a dictionary.

Type:

>>> '''x = {'dog':1}'''

Now Type:

>>> '''x * 5'''

'''Traceback (most recent call last):'''

'''File "<pyshell#5>", line 1, in ?'''

'''x * 5'''

'''TypeError: unsupported operand type(s) for *: 'dict' and 'int''''

You can't do it with dictionaries, that would make more than one of the same key, remember.

===Indexing===
You have already learned how to index in lesson 2. When you typed x[3] you were indexing. You may also index a string without first making a variable represent it.

Type:

>>> '''"I Love Wikipedia"'''[5]

'''e'''

simple enough.

===Slicing===

''Slicing'' is used to access a range of elements the way that ''indexing'' accessess one element.

Type:

>>> '''x = "Wikipedia and Python are awesome"'''

Now Type:

>>> '''print x[14:32]

'''Python are awesome'''

The numbers that you enter after the variable (the [14:32]) are called ''indices''. The way the last one works is hard to understand at first. I'll do another example to make it clear.

Type:

>>> '''x = '1234''''

Now type:

'''print x[1:3]'''

'''23'''

It prints out the 2 because it starts numbering at 0, but the reason it prints out the 3 instead of the 4 is because it counts the '''[3]''' that you entered as the end point and does not include it. Seems wierd at first but easy to get used to.

You may also use negative numbers as the indices '''(x[-12:-])'''. If you only use one negative indice '''(x[-4:])''' Python will print starting with the element selected and go until the end of the string, tuple or list. This works for positive indices as well '''(x[:3])'''. Python will print the first 2 elements of '''x'''.

Another thing that you can do when ''splicing'' is enter the ''step'' indice.

Type:

>>> '''x = "0123456789"'''

Now Type:

>>> '''x[1:-1:3]'''

''' '147' '''

You may also just use the step indice.

Type:

>>> '''x[::3]'''

''''0369''''

You can do this to find every other element or every third or whatever your needs require. You may also make the step indice negative. By doing so you make the elements return starting with the last one.

Type:

>>> '''x='0123456789''''

Now Type:

>>> '''x[-2:1:-1]

''''8765432''''

To reverse a string (or any sequence):

>>> '''x[::-1]

''''9876543210''''

When the step indice is negative it is important to remember to make sure that the first indice is calling an element that comes later in the string, tuple or list than the second element. Just as in the last example '''-2''' is representing '''8''' while '''1''' is representing 2.

I'll have to finish this lesson some other time, my bed is calling me.

===The Format Specifier===

You are going to use this versatile command constantly.

Type:

>>> '''print 'I Love %s' % 'Linux''''

'''I Love Linux'''

What the percent sign does is hold the place in the string and let you tell Python what to put there at the end of the string. The '''s''' behind the '''%'''

[[Category:Computer science]]
[[Category:Programming]]
[[Category:Python]]

Software industry

2008-08-11T13:23:09Z

85.250.147.194: /* External links */

{{globalize}}
{{Expand|date=January 2007}}
[[Image:Packagedsoftwareatretail.jpg|thumb|right|250px|Starting in the 1980s, application software has been sold in mass-produced packages through retailers]]

The '''software industry''' comprises businesses involved in the [[software development|development]], [[software maintenance|maintenance]] and [[software publisher|publication]] of [[computer software]]. The software industry started in the mid-1970s at the time of the personal computer revolution. The industry also includes software [[Service (economics)|service]]s, such as [[training]] and [[consultancy]]. The largest and most profitable of software companies are located in the [[United States]]. As of 2006, the client software industry is dominated by [[Microsoft]]{{Fact|date=March 2008}}. [[Software Magazine]]'s 500 list in 2005 shows the total amount of revenue brought in by software companies per locale, with the highest being [[California]] due to [[Silicon Valley]] and the amount of [[Fortune 500]] software companies residing in that area. <ref>[http://www.softwaremag.com/SW500/index.cfm?StartRow=1&RowsPer=50&BusCat_Search=&PrimBus_Search=&PrimBusCat_Search=&RankSort=ASC&CompSort=&trk=n&id=5 Software Magazine 500] (2005)</ref>

== Overview ==
There are mainly two types of businesses in the software industry; those developing [[proprietary software]] such as [[Microsoft]], and those developing [[open source software]]. Developing proprietary software is costly and involves [[software licensing]] and the need to protect the software from [[Software cracking|cracking]] and [[Software piracy|piracy]].

The main financial return on open source comes from selling services, such as training and support, rather than the software itself. Many contributors to open source software (especially those developing [[software tools]]) also feel that there is a significant long-term return in the form of improved resources and capabilities within the software industry. Despite doing much business in properietary software, some companies like [[Sun Microsystems]] and [[IBM]] participate in developing free and open source software to deter from [[monopoly|monopolies]] and take a portion of their [[market share]]. [[Netscape]]'s actions are an example of this, and thus [[Firefox]] has become more popular <ref>[[Netscape_Navigator#Fall_of_Netscape]]</ref>

== Sectors ==
=== Freeware ===
[[Freeware]] is [[copyright]]ed computer [[software]] which is made available for use free of charge, for an unlimited time, as opposed to [[shareware]] where the user is required to pay (e.g. after some trial period or for additional functionality). Authors of freeware often want to "give something to the community", but also want credit for their software and to retain control of its future development. Sometimes when programmers decide to [[End-of-life (product)|stop developing]] a freeware product, they will give the [[source code]] to another programmer or release the product's source code to the public as [[free software]].

=== Shareware===
[[Shareware]] is a [[marketing]] method for [[computer software]]. Shareware software is typically obtained free of charge, either by downloading from the Internet or on magazine cover-disks. A user tries out the program, and thus shareware has also been known as "try before you buy". A shareware program is accompanied by a request for payment, and the software's distribution license often requires such a payment.

=== Open source ===
[[Open source]] describes the principles and methodologies to promote open access to the '''production''' and '''design''' process for various goods, products, resources and technical [[conclusions]] or advice. The term is most commonly applied to the [[source code]] of software that is made available to the general public with either relaxed or non-existent [[intellectual property]] restrictions. This allows users to create [[user generated content|user-generated software content]] through either incremental individual effort, or [[collaboration]].

=== Commercial ===
'''Commercial software''' is [[computer software]] sold for [[commerce|commercial]] purposes or that serves commercial purposes. Commercial software is most often [[proprietary software]], but [[free software]] is also used as commercial software.<ref>[[Free Software Foundation]]. ''Categories of Free and Non-Free Software''.[http://www.gnu.org/philosophy/categories.html]</ref> All or parts of software packages and services that support commerce are increasingly made available as free software, including products from [[Red Hat]], [[Apple Computer]], [[Sun Microsystems]], and [[Google]]. [[Microsoft Corporation]] uses "commercial software", rather than "proprietary software", to describe their [[business model]].<ref>[http://www.microsoft.com/presspass/exec/craig/05-03sharedsource.mspx Speech Transcript - Craig Mundie, The New York University Stern School of Business]</ref>

== Size of the Industry ==

[[Software Magazine]]s' ''Software 500 survey'' can be used to gauge the value of the commercial software industry. The ''Software 500 survey'' consists of data of the top 500 software companies, as ranked by [[Software Magazine]]. Total worldwide revenues in 2006 for companies in the ''Software 500'' list were $394 billion, representing a growth of 3.5% from 2005, when total Software 500 revenue was $381 billion.<ref>[http://www.softwaremag.com/L.cfm?Doc=984-10/2006 Software Magazine - 2006 Software 500: Deep Concerns Over Security]</ref>

== See also ==
* [[Professional open-source| Professional Open Source Business Model]]
* [[Computer software]]
* [[Software development]]
* [[Software publisher]]
* [[Software engineering]]
* [[World's largest software companies]]

== References ==
<div class="references-small"><references/></div>

== External links ==
{{Wiktionary}}
* [http://www.sao.org/ Software Association of Oregon website]
* [http://www.siprofessionals.org/ Software Industry Professionals website]
* [http://www.siia.net/ Software and Information Industry Association website]
* [http://www.softwaremag.com/ Software Magazine website]
* [http://unisoft-technologies.blogspot.com/ Software Development News]
* [http://software.computerdictionaries.org/ Software Terms] A collection of software dictionaries

[[Category:Industries]]
[[Category:Software industry|*]]

[[ar:صناعة البرمجيات]]
[[es:Industria del software]]