LIS 559: Programming for Library and Information Science Applications

1
LIS 559 Programming for Library and Information
Science Applications

• Summer 2006
• Margaret Kipp
• mkipp_at_uwo.ca
• x88687
• NCB 235

2
Basic Concepts

• Getting Started
• First Programme
• Types
• Strings
• Variables
• Conditionals
• Flow Control Structures
• Namespaces
• Input and Output

3
Getting Started

• Programming Language Python
• ActivePython
• Start -- Programs -- ActiveState ActivePython
• Pythonwin IDE (Integrated Development
  Environment)
• Interactive Python session
• Text editor
• http//www.activestate.com/Products/ActivePython/

4
First Programme

• Type print "Hello, World!"
• This is an extremely simple programme
• print is a builtin Python command
• print has a carriage return at the end, to remove
  this, add a ,
• print "Hello, World!",
• print "Hello, World!"

5
Reserved Words (builtin commands)

• and, assert, break, class, continue, def, del,
  elif, else, except, exec, finally, for, from,
  global, if, import, in, is, lambda, not, or,
  pass, print, raise, return, try, while

6
Variables

• A variable stores programme data.
• A variable has a type. It can be a number, a
  string or something more complex.
• e.g.
• hello "Hello, World!"
• print hello
• hello is a variable of type string

7
Variables (cont.)

• Variables cannot have the same name as a builtin
  command in Python
• Variable names should tell others what the
  variable does
• e.g. 'name' for a person's name, rather than
  'column1'

8
Types

• String
• "python", "Hello, World!"
• Number
• 1, 1.5, 1000
• List
• "apple", "orange", "banana"
• 1,2,3
• Tuple
• (1, 2, 4)
• Dictionary
• "author" "Jane Doe", "title" "This is not a
  book"

9
Numbers

• integers (1, 2, 3), floats (e.g. 1.56)
• basic arithmetic - /
• is the modulo operator or remainder of
  division, e.g. 50 5 0 because 50 is divisible
  by 5
• if a b is not zero, then a is not divisible by
  b
• tests
• lt (less than) gt (greater than)
• (equals) ! (is not equal to)
• gt (greater than or equal to) lt (less than or
  equal to)

10
Strings

• Always start/end with quotes " or ', either 1, 2
  or 3 (3 quotes allow strings to span multiple
  lines)
• a "Hello, World!"
• b "This is a sample programme."
• a0 H
• a1 e
• a2 l
• ...
• a-1 ! (can be used to pick letters from the
  end)

11
Strings (cont.)

• concatenation sticking strings together
• just like adding numbers a b
• a "Hello, World!"
• b "This is a sample programme."
• print a b
• result "Hello, World! This is a sample
  programme."
• length number of letters/numbers in a string
• len()
• print len(a)
• result 13
• print len(b)
• result 27

12
Strings (cont.)

• strip() removes spaces and returns from the end
  of the string
• s "Hello, World! "
• s s.strip()
• print s
• result "Hello, World!"
• split(" ") splits a string
• s "Hello, World!"
• s s.split(" ")
• print s
• result "Hello,", "World!"

13
Strings (cont.)

• find(substring) finds a substring inside the
  string
• s "Hello, World!"
• s s.find("lo")
• print s
• result 3
• replace(substring, new) replaces a substring
  with something new
• s "Hello, World!"
• s s.replace("World","Class")
• result "Hello, Class!"

14
Conditionals

• If-Then
• Used to determine which path the programme will
  take
• a 7
• b 5
• if a lt b
• print str(a) " is less than " str(b)
• elif a gt b
• print str(a) " is greater than " str(b)
• else
• print str(a) " equals " str(b)

15
Flow Control Structures (Loops)

• while loop
• used when the number of times the loop will run
  is not known
• syntax
• i 20
• while i gt 5
• i i / 2
• print i
• result 5
• Note that any lines that are part of the while
  loop must be indented

16
Loops (cont.)

• for loop
• useful where the number of times the loop will
  run is known
• syntax
• j 0
• for i in range(1,5)
• j j 1
• print j
• result 4
• range command
• this command creates a list of numbers, in this
  case 1, 2, 3, 4, 5, it's extremely useful in
  for loops
• or
• for item in allDatabaseEntries
• print item

17
Input and Output

• Output
• print
• e.g.
• print "Hello, World!"
• print 54
• Input
• raw_input()
• e.g.
• name raw_input("What is your name?")

18
Saved Programmes (import)

• import
• used to run programmes typed in a text editor at
  the command line
• can also be used to add other programmes to yours
• import helloworld.py