Slide 1What is Python?BenefitsThe InterpreterSlide 5Example:Using Python as a CalculatorUsing VariablesUsing VariablesStringsNew linesManipulating StringsSubscriptsMore Slice NotationMore Slice NotationListsLists IndicesProgrammingif Statementsfor StatementsUsing range() functionUsing break and else for loopsUsing passDefining FunctionsKeyword ArgumentsSlide 26Introduction to PythonWhat is Python?•Interpreted object oriented high level programming language–No compiling or linking neccesary•Extensible: add new functions or modules to the interpreterBenefits•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 syntaxThe 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 multi-line 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•1.6Using Variables>>> width = 20>>> height = 5*9>>> width * height900>>> x = y = z = 0 # Zero x, y and z>>> x0>>> y0>>> z0Using Variables>>> # try to access an undefined variable... nTraceback (most recent call last):File "<stdin>", line 1, in <module>NameError: name ’n’ is not defined>>> # last printed expression is stored as _>>> price * tax12.5625>>> price + _113.0625Strings>>> ’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 lineshello = "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 containingseveral 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...112358if 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’)...Morefor Statements>>> # Measure some strings:... a = [’cat’, ’window’, ’for’]>>> for x in a:... print(x, len(x))...cat 3window 6for 3Using range() function>>> for i in range(5):... print(i)...01234Using 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 passThe 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 1597Keyword Arguments-May use keyword arguments of the form:keyword = valuedef parrot(voltage, state=’a stiff’, action=’voom’): print("-- This parrot wouldn’t", action, end=’ ’)print("if you put", voltage, "volts through
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