Download PythonFunc

CSC1018F:
Functional Programming
Diving into Python Ch. 16
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
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
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
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
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:
>>> def odd(n):
...
return n % 2
...
>>> li = range(10)
>>> filter(odd, li)
[1,3,5,7,9]
>>> [e for e in li if odd(e)]
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:
>>> def double(n):
...
return n * 2
...
>>> li = range(10)
>>> map(double, li)
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
>>> [double(e) for e in li]
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:
>>> moduleNames = [‘sys’, ‘os’, ‘re’]
>>> modules = map(__import__, moduleNames)
>>> modules
[<module 'sys' (built-in)>, <module 'os' from
'/Library/Frameworks/Python.framework/Versions/2.3/lib/
python2.3/os.pyc'>, <module 're' from
'/Library/Frameworks/Python.framework/Versions/2.3/lib/
python2.3/re.pyc'>]
>>> modules[0].version
'2.3.3 (#2, Dec 23 2003, 22:56:29) \n[GCC 3.1 20020420
(prerelease)]'
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