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Fun with Python Learning a new language in several easy steps. What does a computer language have to do? Data Representation, storage, and Recall: There has to be a way to set variables and to refer to the values they contain. Python has the regular set of things like characters, integers, floating point numbers and strings. It doesn’t have a declaration statement (no int i; like java) nor does it have implicit values like FORTRAN. It doesn’t have arrays, as such. It has lists, tuples and dictionaries. It also uses garbage collection to remove data space that is no longer used – which can have some interesting effects on performance. i= 1 defines an integer i as one. [0,1,2,3] is a list of 4 integers [“CA”, 1., 1.1, 3.] is a list with a string and three floating point numbers (“CA”, 1., 1.1, 3.) is the same data as a tuple [(“CA”,1., 1.1, 3.), (“CA”, 4.8, 1.1,3.)] is a list of tuples { ‘atom1’:”CA”, ‘atom2’:”CB”} is a dictionary “ABC” and ‘XYZ’ are strings Lists, tuples and dictionaries can be indexed and assigned. a = [1,2,3] means a is a list of numbers a[1] is 2 because indexing starts with 0 a[1:] is [2,3] Conditional Operations There has to be a way to check if a logical condition is true or false and use that result to control the operation of the program. if x < 0 : do something elif x == 1: do something else else: do yet another thing Python has continue, pass and break statements but not GOTO’s Basic Numerical and Logical Operations +-*/ // % ** >= == <= > < != and more. Iterative Control Structures Python has for and while loops for a in iterable : # an iterable is something like a list that can be iterated on print a x=0 while x < 100 : x += 1 Input and Output: print x prints the value of x print “x equals “ + x prints “x equals “ followed by the value of x input requires knowing how to open a file (in general) but can work from a standard input (i.e. the terminal) for line in sys.stdin : reads every line in from the terminal line = readline (sys.stdin) reads a line from the terminal Libraries: import sys imports the system library from sys import stdin only imports stdin Methods : Objects -how to extend the things the language knows about