Introduction to Python What is Python Interpreted object oriented high level programming language No compiling or linking neccesary Extensible add new functions or modules to the interpreter Benefits Offers more structure and support for large programs than shell and batch files Modules can be reused No compilation saves development time Easy to read syntax The Interpreter Similar to UNIX Reads and executes commands interactively When called with a file name argument it reads and executes a script from that file Invoking is simple python or python c command arg Script name and additional arguments are passed to sys argv When commands are read from a tty the interpreter is said to be in interactive mode Primary Prompt Secondary Prompt Continuation lines are needed when entering a multiline construct As an example take a look at this if statement Example the world is flat 1 if the world is flat print Be careful not to fall off Be careful not to fall off Using Python as a Calculator 2 2 4 This is a comment 2 2 4 2 2 and a comment on the same line as code 4 50 5 6 4 5 0 8 5 Fractions aren t lost when dividing integers 1 6 Using Variables width 20 height 5 9 width height 900 0 0 0 x y z 0 Zero x y and z x y z Using Variables try to access an undefined variable n Traceback most recent call last File stdin line 1 in module NameError name n is not defined last printed expression is stored as price tax 12 5625 price 113 0625 Strings spam eggs spam eggs doesn t doesn t doesn t doesn t Yes he said Yes he said Yes he said Yes he said Isn t she said Isn t she said New lines hello This is a rather long string containing n several lines of text just as you would do in C n Note that whitespace at the beginning of the line is significant print hello This is a rather long string containing several lines of text just as you would do in C Note that whitespace at the beginning of the line is significant Manipulating Strings word Help A word HelpA word 5 HelpAHelpAHelpAHelpAHelpA str ing string str strip ing string Subscripts word 4 A word 0 2 He word 2 4 lp word 2 The first two characters He word 2 Everything except the first two characters lpA More Slice Notation word 0 x Traceback most recent call last File stdin line 1 in x word 1 xelpA Splat word 4 SplatA word 1 100 elpA word 10 word 2 1 More Slice Notation word 1 The last character A word 2 The last but one character p word 2 The last two characters pA word 2 Everything except the last two characters Hel Lists Most versatile compound data type List items may be different types a spam eggs 100 1234 a spam eggs 100 1234 Lists Indices a 0 spam a 3 1234 a 2 100 a 1 1 eggs 100 a 2 bacon 2 2 spam eggs bacon 4 3 a 3 Boo spam eggs 100 spam eggs 100 spam eggs 100 Boo Programming Fibonacci series the sum of two elements defines the next a b 0 1 while b 10 print b a b b a b 1 1 2 3 5 8 if Statements x int input Please enter an integer Please enter an integer 42 if x 0 x 0 print Negative changed to zero elif x 0 print Zero elif x 1 print Single else print More More for Statements Measure some strings a cat window for for x in a print x len x cat 3 window 6 for 3 Using range function for i in range 5 print i 0 1 2 3 4 Using break and else for loops for n in range 2 10 for x in range 2 n if n x 0 print n equals x n x break else loop fell through without finding a factor print n is a prime number Using pass The pass statement is used for when a statement is required but no action while True pass Busy wait for keyboard interrupt Ctrl C class MyEmptyClass pass Defining Functions def fib n write Fibonacci series up to n Print a Fibonacci series up to n a b 0 1 while b n print b end a b b a b print Now call the function we just defined fib 2000 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 Keyword Arguments May use keyword arguments of the form keyword value def parrot voltage state a stiff action voom print This parrot wouldn t action end print if you put voltage volts through it http docs python org tutorial index html
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