CSC102 INTRO TO PROGRAMMING WITH PYTHON LECTURE 9 PYTHON BEATS YOUR STINKY LANGUAGE: YOU CAN QUOTE ME MICHAEL GROSSBERG

Transcription

1 CSC102 INTRO TO PROGRAMMING WITH PYTHON LECTURE 9 PYTHON BEATS YOUR STINKY LANGUAGE: YOU CAN QUOTE ME MICHAEL GROSSBERG

2 THREE WAYS TO SKIN A STRING SINGLE QUOTES This will give you an error. Must fit in a single line of source DOUBLE QUOTES Also must fit in a single line of source TRIPLE-REPEAT DOUBLE/SINGLE QUOTES This kind of quote can spread over multiple lines. They are often used instead of comments to document source code

3 CONCATENATION ACROSS LINES CONCATENATION x = This will give you an error. x = ( This will not give you + an error. ) x = But this will give you + an error. x = ( Automatic concatenation lets you do this without the plus )

4 SLASH GLUE x = A backslash can also glue lines\ together and not just for string. y = \ 4 + 5! CAN BE TROUBLE, ANY CHARACTER AFTER \ MESSES THINGS UP USE PARENTHESIS FOR FEWER ERRORS x = ( This is so much safer. Why take unnecessary risks? ) y = ( )

5 QUOTES IN QUOTES IF YOU NEED AN APOSTROPHE YOU CAN USE DOUBLE QUOTE STRINGS Let s use a double string quote here IF YOU NEED DOUBLE QUOTES YOU CAN USE SINGLE QUOTES They say, use a single string quote here. YOU CAN USE BOTH IN TRIPLE QUOTE STRINGS """With 3 quotes it's "easy" to use apostrophes and quotes.""" OR With 3 quotes it's "easy" to use apostrophes and quotes.

6 THE GREAT ESCAPES YOU CAN ALSO USE \ TO ESCAPE If we \ escape\ special characters: no problem THIS ALSO WORKS FOR APOSTROPHE Let\ s use a double string quote here FOR A BACKSLASH WE NEED TO DO IT TWICE This is actually a backslash: \\.

7 IT S NOT NOTHING WHITESPACE IS NOT NOTHING A SPACE LOOKS LIKE THIS THIS IS A TAB (CHARACTER) x = #the nothing string x = x = \t THIS IS A NEW LINE (UNIX/MAC OSX) THIS IS A WINDOWS NEW LINE THIS IS AN OLD MAC NEW LINE x = \n x = \r\n x = \r

8 OTHER ESCAPES DOES THIS RING A BELL? x = \a print x,x,x,x BACKSPACE SOMETIMES HANDY x = 'XXXXXXXXXX' print x, print 'O' print x, for ind in range(len(x)): print '\b\b', print 'O' XXXXXXXXXX O O WITHOUT BACKSPACE WITH BACKSPACE

9 STRINGS ARE SEQUENCES F o o B a r x[start:end:step] x[4]== B x[1:]== oo Bar. x[:4]== Foo x[-1]==. x[:-2]== Foo Ba x[::2]== FoBr

10 DON T REPEAT YOUR SELF x = This is completely >>> y = ridiculous. >>> z = sublime. >>> print x+y This is completely ridiculous. >>> print x+z This is completely sublime. >>> x = "Are we there yet?\n" >>> print x*3 Are we there yet? Are we there yet? Are we there yet? ADDITION FOR STRINGS PRODUCTS FOR STRINGS

11 MY STRING IS BIGGER TEST EQUALITY USING == secret_word = 'fish' user_input = raw_input('please type the secret word:') if user_input == secret_word: print "Correct. You know the secret word!" else: print "No. That is not the secret word" SOME STRINGS ARE BIGGER THAN OTHERS >>> 'a' < 'b' >>> 'b' < 'a' False

12 THE SECRET LIFE OF CHARACTERS CHARACTERS ARE REALLY NUMBERS ASCII >>> ord('a') 97 >>> chr(97) 'a' >>> ord('b') 98 >>> ord('z') 122 >>> ord('a') 65

13 COUNTING THE ABCS BY GOING THROUGH THE NUMBERS x = ord('a') print "We present the alphabet: " for ind in range(26): print chr(x+ind), WE CAN GET THE ALPHABET We present the alphabet: a b c d e f g h i j k l m n o p q r s t u v w x y z

14 A < C >>> ord('a') 97 >>> ord('c') 99 >>> 'a' < 'c' >>> 'ab' < 'a' False >>> 'ab' < 'ac' >>> 'az' < 'ba' SINGLE CHARACTERS: GOES BY NUMBER SHORTER STRING FIRST EVALUATE FIRST CHARACTER. ONLY IF TIE, GO TO NEXT CHARACTER

15 MESSED UP PRIORITIES >>> '1' < '2' >>> '11' < '12' >>> '34' < '99' >>> '9' < '10' False >>> 'A' < 'a' >>> ord('a') 65 >>> ord('a') 97 >>> 'B' < 'a' STRING COMPARISON COMPARE FIRST CHARACTER CAPITAL LETTERS COME FIRST

16 MEMBERS ONLY alphabet = 'abcdefghijklmnopqrstuvwxyz' vowels = 'aeiou' for letter in alphabet: print 'Letter ', letter, if letter in vowels: print 'is a vowel.' else: print 'is a consonant.' Letter a is a vowel. Letter b is a consonant. Letter c is a consonant. Letter d is a consonant. Letter e is a vowel....

17 FOR USEFUL THINGS IMPORT STRINGS >>> import string >>> print string.ascii_lowercase abcdefghijklmnopqrstuvwxyz >>> print string.ascii_letters abcdefghijklmnopqrstuvwxyzabcdefghijklmno PQRSTUVWXYZ >>> print string.digits >>> print }~ >>> ' ' in string.whitespace AND THERE ARE MORE (RTFM)

18 STRING IS AN OBJECT OBJECT MEANS DATA X = 5 # 5 IS THE DATA X = HELLO # DATA IS THE SEQUENCE OF CHARACTERS ACTIONS (METHODS) THINGS THE OBJECT CAN DO (OFTEN ON SELF)

19 UPPER/LOWER CASE >>> x = "This is a String" >>> x.upper() 'THIS IS A STRING' >>> x.lower() 'this is a string' >>> x.swapcase() 'this IS A string' >>> x.title() 'This Is A String' >>> x = 'fish paste' >>> x.capitalize() 'Fish paste' MAKE ALL UPPERCASE MAKE ALL LOWERCASE SWAP THE CASE CAPITALIZE FIRST LETTER OF EACH WORD CAPITALIZE FIRST LETTER

20 STRIP SHOW >>> ' spacious '.strip() 'spacious' >>> ' 'example' >>> ' spacious '.rstrip() ' spacious' >>> 'mississippi'.rstrip('ipz') 'mississ' >>> ' spacious '.lstrip() 'spacious ' >>> ' 'example.com' STRIP RSTRIP LSTRIP

21 LEFT, RIGHT, AND CENTER >>> x = "Introduction" >>> ' '+x.center(40)+' ' ' Introduction ' >>> ' '+x.center(40,'=')+' ' ' ==============Introduction============== ' >>> ' '+x.ljust(40,'=')+' ' ' Introduction============================ ' >>> ' '+x.rjust(40,'=')+' ' ' ============================Introduction ' GOOD FOR MAKING CELLS IN TABLES

22 WHAT IS IT? >>> '78'.isalnum() >>> '78fish'.isalnum() >>> '78 fish'.isalnum() False >>> '78.fish'.isalnum() False >>> 'fish'.isalpha() >>> '78'.isalpha() False >>> '78'.isdigit() >>> '78.5'.isdigit() False JUST DIGITS AND LETTERS JUST LETTERS JUST DIGITS LOTS MORE!!

23 DON T START WITH ME user_input = raw_input("a material like steel or tin: ") material = user_input.strip().lower() if material.startswith('me'): print "Don't start with me!" else: print 'No it the answer is "metal," you bonehead!' $ python quiz.py A material like steel or tin: metal Don't start with me! $ python quiz.py A material like steel or tin: cookies No it the answer is "metal," you bonehead! ENDSWITH ANOTHER METHOD

24 EXAMPLE: CAN I HAVE YOUR PHONE NUMBER? user_input = raw_input("enter a 10-digit phone number: ") user_input = user_input.strip().lower() error = False import string number = "" for char in user_input: if char not in string.digits + '-() \t': error = ; break elif char.isdigit(): number += char if not error and len(number)==10: number = '('+number[:3]+') '+number[3:6]+'-'+number[6:] print "The phone number is", number else: error = if error: print "Not a properly formatted 10-digit phone number."

25 THANKS