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CS1001. Python.
November 14th, 2011
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Scripting languages
 Scripting
languages foster an exploratory,
incremental approach to writing code
 Historically
 Favor
interpreted
your time and energy over the CPU’s
 Include
libraries for common tasks
 Examples

AWK [1977], Perl [1987], Python [1991]
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Style
Java: public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello world");
}
}
Python: print “hello world”
Perl: print “hello world\n”;
AWK: BEGIN { print "Hello, world!" }
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Philosophy
More
time
 Thinking
about the problem
 Experimenting with solutions
Less
time
 Writing
code
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Perl
 Larry Wall, 1987
(linguist)
 Report
writing (text processing!)
 “There
is more than one way to do it.”
 What
was text processing essential for in
the early 90s?
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Websites per year (log scale)
Source: http://www.useit.com/alertbox/web-growth.html
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Which is more important?
Code
should be easy to write
Code
should be easy to read
(This is a false dichotomy)
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Obfuscated code contest
`$=`;$_=\%!;($_)=/(.)/;$==++$|;
($.,$/,$,,$\,$",$;,$^,$#,$~,$*,$:,
@%)=($!=~/(.)(.).(.)(.)(.)(.)..(.)(.)
(.)..(.)......(.)/,$"),$=++;$.++;$.+
+;
$_++;$_++;($_,$\,$,)=($~.$"."$;$
/$%[$?]$_$\$,$:$%[$?]",$"&$~,$
#,);$,++;$,++;$^|=$";`$_$\$,$/$:
$;$~$*$%[$?]$.$~$*${#}$%[$?]$
;$\$"$^$~$*.>&$=`
Perl
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Obfuscated code contest
`$=`;$_=\%!;($_)=/(.)/;$==++$|;
($.,$/,$,,$\,$",$;,$^,$#,$~,$*,$:,
@%)=($!=~/(.)(.).(.)(.)(.)(.)..(.)(.)
(.)..(.)......(.)/,$"),$=++;$.++;$.+
+;
$_++;$_++;($_,$\,$,)=($~.$"."$;$
/$%[$?]$_$\$,$:$%[$?]",$"&$~,$
#,);$,++;$,++;$^|=$";`$_$\$,$/$:
$;$~$*$%[$?]$.$~$*${#}$%[$?]$
;$\$"$^$~$*.>&$=`
$
Just another Perl
hacker.
Perl
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Obfuscated code contest
C
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Obfuscated code contest
C
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Python
 Emphasizes
readability
 “There
should be one – and preferably only
one – way to do it.”
 Large
standard library (batteries included)
 Cross
platform and open source
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Parsing text files (and reading
them back!)
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Getting the weather
http://weather.yahooapis.com/forecastrss?w=2459115
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Technically
 Dynamic
typing
 Garbage
collected
 Multi-paradigm
 Compiles
to bytecode
 Exception
based error handling
 Extensible
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Dynamic typing
pi = 3.1459
print pi
pi = "I'd love to have " + str(pi) + " pies"
print pi
print "In fact, I'd like one more"
pi = pi + 1 # TypeError: cannot concatenate 'str' and 'int' objects
print pi
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Books
Ordered by technical complexity - notice anything?
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Internet humor
Source: http://xkcd.com/534/