CSC1018F: Functional Programming

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CSC1018FFunctional Programming

• Diving into Python Ch. 16

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Lecture Outline

• Recap of Regular Expressions week 3
• Functional Programming
• The Zen of Functional Programming
• Finding Path Names
• Filtering and Mapping Revisited
• Revision Exercise Chess Notation

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Recap of Regular Expressions

• A powerful mechanism for identifying patterns in
  text
• But need to be handled with care
• An entirely new syntax is required
• Verbose regular expressions include whitespace
  and comments
• The verbose form is preferred

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Introduction to Functional Programming

• Data-centric thought pattern
• Functions are simply treated as another form of
  data
• Can be operated on and passed as arguments!
• Enables higher level logic and avoid busywork
  coding
• A philosophy of focusing on the data and how it
  needs to be transformed

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Finding Path Names

• Functions useful in finding the name and path of
  the currently executing script
• sys.argv - a list with the name and command line
  arguments of the script
• os.path.dirname(filename) - separates out and
  returns the path portion of filename
• os.path.abspath(pathname) - expands a pathname
  from partial to full. Performs normalization
• os.getcwd() - returns the current working
  directory

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Filtering Lists Differently

• Pass a function and a list to a filter. List
  elements are passed to the function which returns
  True for elements in the final filtered list
• Syntax filter(fn, li)
• fn takes a single argument and evaluates to true
  or false
• Example

gtgtgt def odd(n) ... return n 2 ... gtgtgt li
range(10) gtgtgt filter(odd, li) 1,3,5,7,9 gtgtgt e
for e in li if odd(e)
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Mapping Lists Differently

• Pass a function and a list to a map. List
  elements are passed through the function
• Syntax map(fn, li)
• fn takes a single argument, operates on it and
  returns a new version
• Example

gtgtgt def double(n) ... return n 2 ... gtgtgt li
range(10) gtgtgt map(double, li) 0, 2, 4, 6, 8,
10, 12, 14, 16, 18 gtgtgt double(e) for e in li
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Example Dynamically Importing Modules

• __import__ - a built in function that takes a
  module name as a string and returns the module
• Allows us to load and access modules that are
  only named at run-time
• Example

gtgtgt moduleNames sys, os, re gtgtgt
modules map(__import__, moduleNames) gtgtgt
modules ltmodule 'sys' (built-in)gt, ltmodule 'os'
from '/Library/Frameworks/Python.framework/Version
s/2.3/lib/python2.3/os.pyc'gt, ltmodule 're' from
'/Library/Frameworks/Python.framework/Versions/2.3
/lib/python2.3/re.pyc'gt gtgtgt modules0.version '2
.3.3 (2, Dec 23 2003, 225629) \nGCC 3.1
20020420 (prerelease)'
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Revision Exercise

• You are tasked with coding an anonymization
  program. This replaces names with initials in
  order to hide identity
• To begin, read in a list of names from a file
  idprotect.txt, which contains names in the
  form Firstname and also Firstname Surname on
  separate lines
• The main text should be read in from
  plaintext.txt and all occurrences of idprotect
  names replaced with their corresponding initial.
  Thus John becomes J. and John Smith becomes
  J. S. The final anonymous text should be output
  to the file anontext.txt
• Do this using regular expressions, maps and
  filters, where appropriate