Python

Quick Points About Python Python is an interpreted language –Like Perl you don’t have to compile it –It has a command line interpreter if you want to try things out Python is free –You can download it from: –

No semicolons A new line terminates a statement –No semicolons are needed If you need to continue a long line, you can use a slash \ character at the end print "Hello World" a = "Now is the time for all good men" + \ "to come to the aid of their country" print a

Comments Comments are denoted with a # Comments can also be written as strings that are not used # this is a comment """ Now is the time to comment this line is a comment too bla bla bla """

Indention Matters A block of code has all the lines indented the same number of spaces –That is the only way a block is indicated –No curly braces {} –A block of code ends when the indent level reverts to the level of an outer block

Example Block of Code i = 0 while i < 5 : print i i = i + 1 print "done"

Assigning to Variables Variables can hold strings or numbers i = 5 print i i = "hello" print i Mulitple variables can be assigned at once two, three = 2,3 x, y = y, x # really swaps

Python does NOT convert between strings and numbers automatically You can use the built-in int() function a = 1 b = "2" c = a + int(b)

Strings You can use single or double quotes State = "Maryland" State = 'TN‘ Sentence = """ This is a long sentence that finishes on the another line """

Indexing Strings >>> name1 = "Tom" >>> name2 = "Jones" >>> newname = name1[0] + name2[:3] + "123" >>> print newname TJon123 >>> print newname[-3] 1 >>> print newname[:3] TJo

Lists and Tuples mylist = [ “hello”, 7, “green” ] mytuple = ( “hello”, 7, (“red”, 31) ) firstelement = mylist[0] lastelement = mylist[-1] subtuple = mytuple[1:3] mylist[1] = “newlistvalue” mylist.append( 9 ) mylist.extend( [“new”, “entries”, 50] ) print “List has“, len(mylist), “elements” del mylist[2] del mylist[0:1]

Dictionaries mydict[0] = “first” mydict[1] = “Second” mydict[“zero”] = “First” mydict[“one”] = “Second”

If c == 12: c = 1 for element in mylist: print element