10:
Creating Chapter and Modifying Text
1
2
Text
Text is the universal medium
We can convert any other media to a text representation.
We can convert between media formats using text.
Text is simple.
Like sound, text is usually processed in an arraya long
line of characters
We refer to one of these long line of characters as a string.
In many (especially older) programming languages, text is actually manipulated
as arrays of characters. Its horrible! Python actually knows how to deal with
strings.
3
Strings
Strings are defined with quote marks.
Python actually supports three kinds of quotes:
>>> print 'this is a string'
this is a string
>>> print "this is a string"
this is a string
>>> print """this is a string"""
this is a string
Use the right one that allows you to embed quote
marks you want
>>> aSingleQuote = " '
>>> print aSingleQuote
'
"
4
Why would you want to use triple quotes?
To have long quotations
with returns and such
inside them.
>>> print aLongString()
This is a
long
string
>>>
def aLongString():
return """This is a
long
string"""
5
Encodings for strings
Strings are just arrays of characters
In most cases, characters are just single bytes.
The ASCII encoding standard maps between single byte
values and the corresponding characters
More recently, characters are two bytes.
Unicode uses two bytes per characters so that there are
encodings for glyphs (characters) of other languages
Java uses Unicode. The version of Python we are using is
based in Java, so our strings are actually using Unicode.
6
ASCII encoding through
ord()
>>> str = "Hello"
>>> for char in str:
...
print ord(char)
...
72
101
108
108
111
7
There are more characters than
we can type
Our keyboards dont have all the characters available to
us, and its hard to type others into strings.
Backspace
Return
We use backslash escapes to get other characters into
strings
8
Backslash escapes
\b is backspace
\n is a newline (like pressing the Enter key)
\t is a tab
\uXXXX is a Unicode character, where XXXX is a
code and each X can be 0-9 or A-F.
http://www.unicode.org/charts/
Must precede the string with u for Unicode to work
9
Testing strings
>>> print "hello\tthere\nMark"
hello there
Mark
>>> print u"\uFEED"
>>> print u"\u03F0"
>>> print "This is\na test"
This is
a test
10
Manipulating strings
We can add strings and get their lengths using the kinds of
programming features weve seen previously.
>>> hello = "Hello"
>>> print len(hello)
5
>>> mark = ", Mark"
>>> print len(mark)
6
>>> print hello+mark
Hello, Mark
>>> print len(hello+mark)
11
11
Getting parts of strings
We use the square bracket [] notation to get parts of
strings.
string[n] gives you the nth character in the string
string[n:m] gives you the nth up to (but not including) the
mth character.
string[0:len(string)] is the whole string
12
Getting parts of strings
>>> hello = "Hello"
>>> print hello[1]
e
>>> print hello[0]
H
>>> print hello[2:4]
ll
H
e
l
l
o
0
1
2
3
4
13
Start and end assumed if not
there
>>> print hello
Hello
>>> print hello[:3]
Hel
>>> print hello[3:]
lo
>>> print hello[:]
Hello
14
Dot notation
All data in Python are actually objects
Objects not only store data, but they respond to special
functions that only objects of the same type understand.
We call these special functions methods
Methods are functions known only to certain objects
To execute a method, you use dot notation
object.method()
15
Capitalize is a method known
only to strings
>>> test="this is a test."
>>> print test.capitalize()
This is a test.
>>> print capitalize(test)
#not a function!
A local or global name could not be found.
NameError: capitalize
>>> print 'this is another test'.capitalize()
This is another test
>>> print 12.capitalize() #12 is not a string!
A syntax error is contained in the code -- I can't read it as Python.
16
Useful string methods
startswith(prefix) returns true if the string starts with the
given suffix
endswith(suffix) returns true if the string ends with the
given suffix
find(findstring) and find(findstring,start) and
find(findstring,start,end) finds the findstring in the object
string and returns the index number where the string starts.
You can tell it what index number to start from, and even
where to stop looking. It returns -1 if it fails.
There is also rfind(findstring) (and variations) that
searches from the end of the string toward the front.
17
Demonstrating startswith
>>> letter = "Mr. Mark Guzdial requests the pleasure of
your company..."
>>> print letter.startswith("Mr.")
Python uses 0
1
as false and 1
>>> print letter.startswith("Mrs.")
as true
0
18
Demonstrating endswith
>>> filename="barbara.jpg"
>>> if filename.endswith(".jpg"):
...
print "It's a picture"
...
It's a picture
19
Demonstrating find
>>> print letter
Mr. Mark Guzdial requests the pleasure of your company...
>>> print letter.find("Mark")
4
>>> print letter.find("Guzdial")
9
>>> print len("Guzdial")
7
>>> print letter[4:9+7]
Mark Guzdial
>>> print letter.find(Fred")
-1
20
Interesting string methods
upper() translates the string to uppercase
lower() translates the string to lowercase
swapcase() makes all upper->lower and vice versa
title() makes just the first characters uppercase and the
rest lower.
isalpha() returns true if the string is not empty and all
letters
isdigit() returns true if the string is not empty and all
numbers
21
Replace method
>>> print letter
Mr. Mark Guzdial requests the pleasure of your company...
>>> letter.replace("a","!")
'Mr. M!rk Guzdi!l requests the ple!sure of your comp!ny...'
>>> print letter #it doesnt change letter unless you store
the result.
Mr. Mark Guzdial requests the pleasure of your company...
22
Strings are sequences
>>> for i in "Hello":
... print i
...
H
e
l
l
o
23
Lists
Weve seen lists beforethats what range() returns.
Lists are very powerful structures.
Lists can contain strings, numbers, even other lists.
They work very much like strings
You get pieces out with []
You can add lists together
You can use for loops on them
We can use them to process a variety of kinds of data.
24
Demonstrating lists
>>> mylist = ["This","is","a", 12]
>>> print mylist
['This', 'is', 'a', 12]
>>> print mylist[0]
This
>>> for i in mylist:
...
print i
...
This
is
a
12
>>> print mylist + ["Really!"]
['This', 'is', 'a', 12, 'Really!']
25
Useful methods to use with lists:
But these ones dont work with strings
append(something) puts something in the list at the end.
remove(something) removes something from the list
if its there.
sort() puts the list in alphabetical order
reverse() reverses the list
count(something) tells you the number of times that
something is in the list.
max() and min() are methods (weve seen them before)
that take a list as input and give you the maximum and
minimum value in the list.
26
Converting from strings to
lists
>>> print letter.split(" ")
['Mr.', 'Mark', 'Guzdial', 'requests', 'the', 'pleasure', 'of',
'your', 'company...']
>>>words = letter.split(" )
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Extended Split Example
def phonebook():
return """
Mary:893-0234:Realtor:
Fred:897-2033:Boulder crusher:
Barney:234-2342:Professional bowler:"""
def findPhone(person):
for people in phones():
def phones():
if people[0] == person:
phones = phonebook()
print "Phone number
phonelist = phones.split('\n')
for",person,"is",people[1]
newphonelist = []
for list in phonelist:
newphonelist = newphonelist + [list.split(":")]
return newphonelist
28
Running the Phonebook
>>> print phonebook()
Mary:893-0234:Realtor:
Fred:897-2033:Boulder crusher:
Barney:234-2342:Professional bowler:
>>> print phones()
[[''], ['Mary', '893-0234', 'Realtor', ''], ['Fred', '897-2033', 'Boulder crusher',
''], ['Barney', '234-2342', 'Professional bowler', '']]
>>> findPhone('Fred')
Phone number for Fred is 897-2033
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Strings have no font
Strings are only the characters of text displayed
WYSIWYG (What You See is What You Get)
WYSIWYG text includes fonts and styles
The font is the characteristic look of the letters in all sizes
The style is typically the boldface, italics, underline, and
other effects applied to the font
In printers terms, each style is its own font
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Encoding font information
Font and style information is often encoded as style runs
A separate representation from the string
Indicates bold, italics, or whatever style modification; start
character; and end character.
The old brown fox runs.
Could be encoded as:
"The old brown fox runs."
[[bold 0 6] [italics 5 12]]
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How do we encode all that?
Is it a single value? Not really.
Do we encode it all in a complex list? We could.
How do most text systems handle this?
As objects
Objects
have data, maybe in many parts.
Objects know how to act upon their data.
Objects methods may be known only to that object, or
may be known by many objects, but each object performs
that method differently.
32
What can we do with all this?
Answer: Just about anything!
Strings and lists are about as powerful as one gets in
Python
By powerful, we mean that we can do a lot of different kinds of computation
with them.
Examples:
Pull up a Web page and grab information out of it, from within a function.
Find a nucleotide sequence in a string and print its name.
Manipulate functions source
But first, we have to learn how to manipulate files
33
Files: Places to put strings and
other stuff
Files are these named large collections of bytes.
Files typically have a base name and a suffix
barbara.jpg has a base name of barbara and a suffix of
.jpg
Files exist in directories (sometimes called folders)
Tells us that the file 640x480.jpg is
in the folder mediasources in the
folder ip-book on the disk C:
34
Directories
Directories can contain files or other directories.
There is a base directory on your computer, sometimes
called the root directory
A complete description of what directories to visit to get
to your file is called a path
35
We call this structure a tree
C:\
C:\ is the root of the tree.
It has branches, each of
which is a directory
Any directory (branch)
can contain more
directories (branches) and
files (leaves)
Documents
and Settings
Windows
Mark
Guzdial
mediasources
cs1315
640x480.jpg
36
Why do I care about all this?
If youre going to process files, you need to know where
they are (directories) and how to specify them (paths).
If youre going to do movie processing, which involves
lots of files, you need to be able to write programs that
process all the files in a directory (or even several
directories) without having to write down each and every
name of the files.
37
Using lists to represent trees
>>> tree = [["Leaf1","Leaf2"],[["Leaf3"],
["Leaf4"],"Leaf5"]]
>>> print tree
[['Leaf1', 'Leaf2'], [['Leaf3'], ['Leaf4'], 'Leaf5']]
>>> print tree[0]
['Leaf1', 'Leaf2']
>>> print tree[1]
[['Leaf3'], ['Leaf4'], 'Leaf5']
>>> print tree[1][0]
['Leaf3']
Leaf1
>>> print tree[1][1]
['Leaf4']
>>> print tree[1][2]
Leaf5
Leaf5
Leaf3
Leaf2
Leaf4
The Point: Lists allow us to
represent complex
relationships, like trees
38
How to open a file
For reading or writing a file (getting characters out or
putting characters in), you need to use open
open(filename,how) opens the filename.
If you dont provide a full path, the filename is assumed to be in the same
directory as JES.
how is a two character string that says what you want to
do with the string.
rt means read text
wt means write text
rb and wb means read or write bytes
We wont do much of that
39
Methods on files:
Open returns a file object
open() returns a file object that you use to manipulate the
file
Example: file=open(myfile,wt)
file.read() reads the whole file as a single string.
file.readlines() reads the whole file into a list where each
element is one line.
read() and readlines() can only be used once without closing and reopening the
file.
file.write(something) writes something to the file
file.close() closes the filewrites it out to the disk, and
wont let you do any more to it without re-opening it.
40
Reading a file
>>> program=pickAFile()
>>> print program
C:\Documents and Settings\Mark Guzdial\My Documents\py-programs\littlepicture.py
>>> file=open(program,"rt")
>>> contents=file.read()
>>> print contents
def littlepicture():
canvas=makePicture(getMediaPath("640x480.jpg"))
addText(canvas,10,50,"This is not a picture")
addLine(canvas,10,20,300,50)
addRectFilled(canvas,0,200,300,500,yellow)
addRect(canvas,10,210,290,490)
return canvas
>>> file.close()
41
Reading a file by lines
>>> file=open(program,"rt")
>>> lines=file.readlines()
>>> print lines
['def littlepicture():\n', '
canvas=makePicture(getMediaPath("640x480.jpg"))\n', '
addText(canvas,10,50,"This is not a picture")\n', '
addLine(canvas,10,20,300,50)\n', '
addRectFilled(canvas,0,200,300,500,yellow)\n', '
addRect(canvas,10,210,290,490)\n', ' return canvas']
>>> file.close()
42
Silly example of writing a file
>>> writefile = open("myfile.txt","wt")
>>> writefile.write("Here is some text.")
>>> writefile.write("Here is some more.\n")
>>> writefile.write("And now we're done.\n\nTHE END.")
>>> writefile.close()
>>> writefile=open("myfile.txt","rt")
>>> print writefile.read()
Here is some text.Here is some more.
And now we're done.
Notice the \n
to make new
lines
THE END.
>>> writefile.close()
43
How you get spam
def formLetter(gender ,lastName ,city ,eyeColor ):
file = open("formLetter.txt","wt")
file.write("Dear ")
if gender =="F":
file.write("Ms. "+lastName+":\n")
if gender =="M":
file.write("Mr. "+lastName+":\n")
file.write("I am writing to remind you of the offer ")
file.write("that we sent to you last week. Everyone in ")
file.write(city+" knows what an exceptional offer this is!")
file.write("(Especially those with lovely eyes of"+eyeColor+"!)")
file.write("We hope to hear from you soon .\n")
file.write("Sincerely ,\n")
file.write("I.M. Acrook , Attorney at Law")
file.close ()
44
Trying out our spam
generator
>>> formLetter("M","Guzdial","Decatur","brown")
Dear Mr. Guzdial:
I am writing to remind you of the offer that we
sent to you last week. Everyone in Decatur knows what
an exceptional offer this is!(Especially those with
lovely eyes of brown!)We hope to hear from you soon.
Sincerely,
I.M. Acrook,
Attorney at Law
Only use this power for good!
45
Writing a program to write
programs
First, a function that will automatically change the text
string that the program littlepicture draws
As input, well take a new filename and a new string.
Well find() the addText, then look for the first double
quote, and then the final double quote.
Then well write out the program as a new string to a new
file.
46
Changing the little program changeLittle(filename,newstring):
# automatically
def Get the original file contents
programfile=r"C:\Documents and Settings\Mark Guzdial\My Documents\pyprograms\littlepicture.py"
file = open(programfile,"rt")
contents = file.read()
file.close()
# Now, find the right place to put our new string
addtext = contents.find("addText")
firstquote = contents.find('"',addtext) #Double quote after addText
endquote = contents.find('"',firstquote+1) #Double quote after firstquote
# Make our new file
newfile = open(filename,"wt")
newfile.write(contents[:firstquote+1]) # Include the quote
newfile.write(newstring)
newfile.write(contents[endquote:])
newfile.close()
47
changeLittle("sample.py","Here is a sample
of changing a program")
Original:
def littlepicture():
Modified:
def littlepicture():
canvas=makePicture(getMediaPath("6
40x480.jpg"))
addText(canvas,10,50,"This is not a
picture")
addLine(canvas,10,20,300,50)
canvas=makePicture(getMediaPath("6
40x480.jpg"))
addText(canvas,10,50,"Here is a sample
of changing a program")
addLine(canvas,10,20,300,50)
addRectFilled(canvas,0,200,300,500,y
ellow)
addRect(canvas,10,210,290,490)
return canvas
addRectFilled(canvas,0,200,300,500,y
ellow)
addRect(canvas,10,210,290,490)
return canvas
48
Thats how vector-based
drawing programs work!
Editing a line in AutoCAD doesnt change the pixels.
It changes the underlying representation of what the line
should look like.
It then runs the representation and creates the pixels all
over again.
Is that slower?
Who cares? (Refer to Moores Law)
49
Finding data on the Internet
The Internet is filled with wonderful data, and almost all
of it is in text!
Later, well write functions that directly grab files from
the Internet, turn them into strings, and pull information
out of them.
For now, lets assume that the files are on your disk, and
lets process them from there.
50
Example: Finding the nucleotide sequence
There are places on the Internet
where you can grab DNA
sequences of things like
parasites.
What if youre a biologist and
want to know if a sequence of
nucleotides that you care about
is in one of these parasites?
We not only want to know
yes or no, but which
parasite.
51
What the data looks like
>Schisto unique AA825099
gcttagatgtcagattgagcacgatgatcgattgaccgtgagatcgacga
gatgcgcagatcgagatctgcatacagatgatgaccatagtgtacg
>Schisto unique mancons0736
ttctcgctcacactagaagcaagacaatttacactattattattattatt
accattattattattattattactattattattattattactattattta
ctacgtcgctttttcactccctttattctcaaattgtgtatccttccttt
52
How are we going to do it?
First, we get the sequences in a big string.
Next, we find where the small subsequence is in the big
string.
From there, we need to work backwards until we find >
which is the beginning of the line with the sequence name.
From there, we need to work forwards to the end of the
line. From > to the end of the line is the name of the
sequence
Yes, this is hard to get just right. Lots of debugging prints.
53
The code that does it
def findSequence(seq):
sequencesFile = getMediaPath("parasites.txt")
file = open(sequencesFile,"rt")
sequences = file.read()
file.close()
# Find the sequence
seqloc = sequences.find(seq)
#print "Found at:",seqloc
if seqloc <> -1:
# Now, find the ">" with the name of the sequence
nameloc = sequences.rfind(">",0,seqloc) # using rfind() here!!
#print "Name at:",nameloc
endline = sequences.find("\n",nameloc)
print "Found in ",sequences[nameloc:endline]
if seqloc == -1:
print "Not found"
54
Why -1?
If .find or .rfind dont find something, they return -1
If they return 0 or more, then its the index of where the
search string is found.
Whats <>?
Thats notation for not equals
You can also use !=
55
Running the program
>>> findSequence("tagatgtcagattgagcacgatgatcgattgacc")
Found in >Schisto unique AA825099
>>> findSequence("agtcactgtctggttgaaagtgaatgcttccaccgatt")
Found in >Schisto unique mancons0736
56
Example: Get the
temperature
The weather is always available
on the Internet.
Can we write a function that
takes the current temperature
out of a source like
http://www.ajc.com/weather or
http://www.weather.com?
57
The Internet is mostly text
Text is the other unimedia.
Web pages are actually text in the format called HTML
(HyperText Markup Language)
HTML isnt a programming language,
its an encoding language.
It defines a set of meanings for certain characters, but one
cant program in it.
We can ignore the HTML meanings for now, and just
look at patterns in the text.
58
Wheres the temperature?
The word temperature
doesnt really show up.
But the temperature always
follows the word Currently,
and always comes before the
<b>&deg;</b>
<td ><img
src="/sharedlocal/weather/images/ps.gif"
width="48" height="48"
border="0"><font size=2><br></font><font
size="-1" face="Arial, Helvetica, sansserif"><b>Currently</b><br>
Partly sunny<br>
<font
size="+2">54<b>&deg;</b></font>
<font face="Arial, Helvetica, sansserif"
size="+1">F</font></font></td>
</tr>
59
We can use the same algorithm weve seen
previously
Grab the content out of a file in a big string.
(Weve saved the HTML page previously.
Soon, well see how to grab it directly.)
Find the starting indicator (Currently)
Find the ending indicator (<b>&deg;)
Read the previous characters
60
Finding the temperature
def findTemperature():
weatherFile = getMediaPath("ajc-weather.html")
file = open(weatherFile,"rt")
weather = file.read()
file.close()
# Find the Temperature
curloc = weather.find("Currently")
if curloc <> -1:
# Now, find the "<b>&deg;" following the temp
temploc = weather.find("<b>&deg;",curloc)
tempstart = weather.rfind(">",0,temploc)
print "Current temperature:",weather[tempstart+1:temploc]
if curloc == -1:
print "They must have changed the page format -- can't find the temp"
61
Adding new capabilities: Modules
What we need to do is to add capabilities to Python that
we havent seen so far.
We do this by importing external modules.
A module is a file with a bunch of additional functions and
objects defined within it.
Some kind of module capability exists in virtually every programming language.
By importing the module, we make the modules
capabilities available to our program.
Literally, we are using the module, as if wed typed it into our file.
62
Pythons Standard Library
Python has an extensive
library of modules that
come with it.
The Python standard
library includes modules
that allow us to access the
Internet, deal with time,
generate random numbers,
andaccess files in a
directory.
63
Accessing pieces of a
module
We access the additional capabilities of a module using
dot notation, after we import the module.
How do you know what pieces are there?
Check the documentation.
Python comes with a Library Guide.
There are books like Python Standard Library that describe
the modules and provide examples.
64
The OS Module
The OS module offers a number of powerful capabilities
for dealing with files, e.g., renaming files, finding out
when a file was last modified, and so on.
We start accessing the OS module by typing:
import os
The function that knows about directories is listdir(),
used as os.listdir()
listdir takes a path to a directory as input.
65
Using os.listdir
>>> import os
>>> print getMediaPath("barbara.jpg")
C:\Documents and Settings\Mark Guzdial\My
Documents\mediasources\barbara.jpg
>>> print getMediaPath("pics")
Note: There is no file at C:\Documents and Settings\Mark Guzdial\My
Documents\mediasources\pics
C:\Documents and Settings\Mark Guzdial\My
Documents\mediasources\pics
>>> print os.listdir("C:\Documents and Settings\Mark Guzdial\My
Documents\mediasources\pics")
['students1.jpg', 'students2.jpg', 'students5.jpg', 'students6.jpg',
'students7.jpg', 'students8.jpg']
66
Writing a program to title pictures
Well input a directory
Well use os.listdir() to get each filename in the directory
Well open the file as a picture.
Well title it.
Well save it out as titled- and the filename.
67
Titling Pictures
import os
def titleDirectory(dir):
for file in os.listdir(dir):
picture = makePicture(file)
addText(picture,10,10,"This is from My CS CLass")
writePictureTo(picture,"titled-"+file)
68
Okay, that didnt work
>>> titleDirectory("C:\Documents and Settings\Mark
Guzdial\My Documents\mediasources\pics")
makePicture(filename): There is no file at students1.jpg
An error occurred attempting to pass an argument to a
function.
69
Why not?
Is there a file where we tried to open the picture?
Actually, no. Look at the output of os.listdir() again
>>> print os.listdir("C:\Documents and Settings\Mark
Guzdial\My Documents\mediasources\pics")
['students1.jpg', 'students2.jpg', 'students5.jpg',
'students6.jpg', 'students7.jpg', 'students8.jpg']
The strings in the list are just the base names
No paths
70
Creating paths
If the directory string is in the placeholder variable dir,
then dir+file is the full pathname, right?
Closeyou still need a path delimiter, like /
But its different for each platform!
Python gives us a notation that works: // is as a path
delimiter for any platform.
So: dir+//+file
71
A Working Titling Program
import os
def titleDirectory(dir):
for file in os.listdir(dir):
print "Processing:",dir+"//"+file
picture = makePicture(dir+"//"+file)
addText(picture,10,10,"This is from My CS Class")
writePictureTo(picture,dir+"//"+"titled-"+file)
72
Showing it work
>>> titleDirectory("C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics")
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students1.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students2.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students5.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students6.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students7.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students8.jpg
>>> print os.listdir("C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics")
['students1.jpg', 'students2.jpg', 'students5.jpg', 'students6.jpg', 'students7.jpg', 'students8.jpg', 'titledstudents1.jpg', 'titled-students2.jpg', 'titled-students5.jpg', 'titled-students6.jpg', 'titled-students7.jpg',
'titled-students8.jpg']
73
Inserting a copyright on pictures
74
What if you want to make sure youve got
JPEG files?
import os
def titleDirectory(dir):
for file in os.listdir(dir):
print "Processing:",dir+"//"+file
if file.endswith(".jpg"):
picture = makePicture(dir+"//"+file)
addText(picture,10,10,"This is from My CS Class")
writePictureTo(picture,dir+"//"+"titled-"+file)
75
Say, if thumbs.db is there
>>> titleDirectory("C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics")
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students1.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students2.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students5.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students6.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students7.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//students8.jpg
Processing: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics//Thumbs.db
>>> print os.listdir("C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\pics")
['students1.jpg', 'students2.jpg', 'students5.jpg', 'students6.jpg', 'students7.jpg', 'students8.jpg', 'Thumbs.db',
'titled-students1.jpg', 'titled-students2.jpg', 'titled-students5.jpg', 'titled-students6.jpg', 'titled-students7.jpg',
'titled-students8.jpg']
76
Another interesting module: Random
>>> import random
>>> for i in range(1,10):
...
print random.random()
...
0.8211369314193928
0.6354266779703246
0.9460060163520159
0.904615696559684
0.33500464463254187
0.08124982126940594
0.0711481376807015
0.7255217307346048
0.2920541211845866
77
Randomly choosing words from a list
>>> for i in range(1,5):
...
print random.choice(["Here", "is", "a", "list", "of",
"words", "in","random","order"])
...
list
a
Here
list
78
Randomly generating
language
Given a list of nouns,
verbs that agree in tense and number,
and object phrases that all match the verb,
We can randomly take one from each to make sentences.
79
Random sentence generator
import random
def sentence():
nouns = ["Mark", "Adam", "Angela", "Larry", "Jose", "Matt", "Jim"]
verbs = ["runs", "skips", "sings", "leaps", "jumps", "climbs", "argues",
"giggles"]
phrases = ["in a tree", "over a log", "very loudly", "around the bush",
"while reading the newspaper"]
phrases = phrases + ["very badly", "while skipping","instead of grading",
"while typing on the Internet."]
print random.choice(nouns), random.choice(verbs),
random.choice(phrases)
80
Running the sentence generator
>>> sentence()
Jose leaps while reading the newspaper
>>> sentence()
Jim skips while typing on the Internet.
>>> sentence()
Matt sings very loudly
>>> sentence()
Adam sings in a tree
>>> sentence()
Adam sings around the bush
>>> sentence()
Angela runs while typing on the Internet.
>>> sentence()
Angela sings around the bush
>>> sentence()
Jose runs very badly
81
How much smarter can we make this?
Can we have different kinds of lists so that, depending on
the noun selected, picks the right verb list to get a match
in tense and number?
How about reading input from the user, picking out key
words, then generating an appropriate response?
if input.find(mother) <> -1:
print Tell me more about your mother
82
Joseph Weizenbaums
Eliza
Created a program that acted like a therapist.
Echoing back to the user whatever they said, as a question.
It had rules that triggered on key words in the users
statements.
It had a little memory of what it had said before.
People really believed it was a real therapist!
Convinced Weizenbaum of the dangers of computing.
83
Session with the Doctor
>>>My mother bothers me.
Tell me something about your family.
>>>My father was a caterpillar.
Note that this is
all generated
automatically.
You seem to dwell on your family.
>>>My job isn't good either.
Is it because of your plans that you say your job is not good either?
84
Many other Python Standard
Libraries
datetime and calendar know about dates.
What day of the week was the US Declaration
of Independence signed? Thursday.
math knows about sin() and sqrt()
zipfile knows how to make and read .zip files
email lets you (really!) build your own spam
program, or filter spam, or build an email tool
for yourself.
SimpleHTTPServer is a complete working
Web server.
85