Introduction to USF's AI Program: Python Programming - Prof. Christopher H. Brooks, Study notes of Computer Science

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Artificial Intelligence Programming

Python Intro^ Chris BrooksDepartment of Computer ScienceUniversity of San Francisco

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2b-0:^ What is Python?

Python is:^ High-level^ Object-oriented^ Free, open-source^ Dynamically typed^ Has a large collection of utility libraries^ garbage-collected^ Mixable - works nicely as a “glue” language^ Easy to learn/use

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2b-2:^ Invoking Python Programs

There are four ways to run a Python program:^ Interactively^ From the command line^ As a script^ From another program

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2b-3:^ Python Implementations

/usr/bin/python on all unix machines IDLE and PythonWin on Windows MacPython on Macintosh Also for Amiga, PalmOS, BeOS, etc.

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2b-5:^ Basic Python

Python has a nice set of built-in data types^ Numbers^ Strings^ Lists^ Dictionaries^ Files Using built-in types makes your code easier towrite/maintain, more portable, and more efficient.

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2b-6:^ Numbers

Numbers work like we’d expect. There are integers, equivalent to longs in C. (1, -31311,4000) There are^ long integers

, which are of unlimited size (31111L, 12345l) There are floats, equivalent to doubles in C.1.23, 3.1e+5 There are Octal and Hexadecimal representations as in C.(0155, 0x3af5) There are complex numbers, as in Lisp, Matlab, etc.(3.0+4j)

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2b-8:^ Strings

One of Python’s strong suits is its ability to work withstrings. Strings are denoted with double quotes, as in C. s1 + s2 - concatenation s1 * 3 - repitition s1[i] - indexing, s1[i:j] - slicing s1[-1] - last character “a % parrot” % “dead” - formatting for char in s1 - iteration

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2b-9:^ Strings

Strings are immutable sequences - to change them, weneed to make a copy.^ Can’t do: s1[3] = ’c’^ Must do: s2 = s1[0:2] + ’c’ + s1[3:]

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2b-11:^ Dictionaries

A Dictionary is a Python hash table (or associative list) Unordered collections of arbitrary objects. d1 = {} - new hashtable d2 = {’spam’ : 2, ’eggs’, 3} Can index by key d2[’spam’] Can have nested Hashtables^ d3 = {’spam’ : 1, ’other’ :{’eggs’ :2, ’spam’ : 3}}^ d3[’other’][’spam’] has_key, keys(), values(), for k in keys() Typically, you’ll insert/delete with:^ d3[’spam’] = ’delicious!’^ del d3[’spam’]

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2b-12:^ Tuples

Tuples are like immutable lists. Nice for dealing with enumerated types. Can be nested and indexed. t1 = (1,2,3), t2 = (1,2,(3,4,5)) Can index, slice, length, just like lists.^ t1[3], t1[1:2], t1[-2] Tuples are mostly useful when you want to have a list of apredetermined size/length.

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2b-14:^ Files

outfile.write(S) - write the string S into the file. outfile.writelines(L) - write the list of strings L into the file. outfile.close() (this is also done by the garbage collector)

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2b-15:^ Basic Python statements

Python uses dynamic typing.^ No need to pre-define variables. Variables are instantiated by assigning values to them^ Referencing a variable before assignment is an error You can assign multiple variables simultaneously spam^ =^4 eggs^ =^5 spam,^ eggs^ = eggs,

spam spam,^ eggs^ = 4,

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2b-17:^ Printing

We’ve already seen the basic print.^ print “hello world” To use a formatting string, do:^ print “hello %s” % “bob”^ print "%s %s" % ("hello" , "world") To suppress the linefeed, include a ,

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2b-18:^ Conditionals

The general format for an if statement is: if^ ^ : elif:^ ^

: else: Notice the colons after the conditionals. Compound statements consist of the colon, followed by anindented block.

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