Lab 1: Course Intro, Getting Started with Python IDLE. Ling 1330/2330 Computational Linguistics Na-Rae Han

Transcription

1 Lab 1: Course Intro, Getting Started with Python IDLE Ling 1330/2330 Computational Linguistics Na-Rae Han

2 Objectives Course Introduction Student survey Introduction to Python 3 Try out Python IDLE (Interactive DeveLopment Environment) Learn Python basic syntax print command Strings Variables Learn to get around in Python IDLE Restarting IDLE session 8/28/2018 2

3 How to do well in this course 1. Be hard-working. If you are new to programming, expect to put in 4-credit worth of work. 2. Be detail-oriented. Do not skim for "important" stuff! You should learn everything. Pay attention to instructions & details when doing homework. 3. Be organized. Class moves fast, and there are a lot of assignments. 4. Be persistent. Coding has frustrating moments. Keep at it! 5. Ask for help. When you had enough of hair-pulling, /office hours. 8/28/2018 3

4 Your first code 1. Open up a new window ("File" > "New Window", or Ctrl+n). 2. Python editor window opens up. Type in: 3. Save the script as "hello.py". print('hello, world!') 4. Run the script by selecting "Run" > "Run Module" or F5. 5. Success! The command executes in the IDLE shell window. Python SCRIPT file IDLE shell (Python interpreter)

5 Scripts can be edited and saved More lines of code added to the script Script is run again; shell re-starts and then executes 8/28/2018 5

6 Following up a script in shell Variable name is available in shell for subsequent commands 8/28/2018 6

7 Try it out 1 minute 8/28/2018 7

8 Operating in shell >>> print('hello', 'world!') Hello world! >>> 4 * >>> In IDLE shell window, Python interprets and responds to each line of code you type in. called a command prompt 8/28/2018 8

9 >>> print('hello', 'world!') Hello world! >>> 4 * >>> print(4 * 12) 48 >>> * >>> 1+4*12 49 >>> (1 + 4 * 12) / >>> prints two strings as two words returns value prints value white space is optional with these operators Parentheses ( ) are used to override precedence 8/28/2018 9

10 Variable assignment Variable name >>> salary = 4500*12 >>> print(salary) Variable assignment operator Expression: variable content VALUE is what s stored, not the expression itself 8/28/

11 Printing vs. returning Prints string content >>> who = 'Homer' >>> print(who) Homer >>> who 'Homer' >>> Evaluates expression, returns the value. Value is a string: note the quotes! 8/28/

12 >>> who = 'Homer' >>> print(who) Homer >>> who 'Homer' >>> salary = 4500 *12 >>> salary >>> print(who, 'makes', salary, 'dollars a year.') Homer makes dollars a year. >>> who = 'Mr. Burns' >>> salary = 50000*12 >>> print(who, 'makes', salary, 'dollars a year.') Mr. Burns makes dollars a year. 8/28/

13 Changing variable value Variable value is declared and then changed >>> who = 'Homer' >>> print(who) Homer >>> who 'Homer' >>> salary = 4500 *12 >>> salary >>> print(who, 'makes', salary, 'dollars a year.') Homer makes dollars a year. >>> who = 'Mr. Burns' >>> salary = 50000*12 >>> print(who, 'makes', salary, 'dollars a year.') Mr. Burns makes dollars a year. 8/28/

14 Variables, variables 2 minutes >>> greet = 'Hello,' >>> nameis = 'my name is' >>> name = 'Homer' >>> print(greet, nameis, name) Hello, my name is Homer >>> >>> name = 'Marge' >>> print(greet, nameis, name) Hello, my name is Marge >>> >>> greet = 'Good morning everyone,' >>> print(greet, nameis, name) Good morning everyone, my name is Marge Same command. Use command history! Ctrl+p/n (Mac)* Alt+p/n (Win)* *It could be up/down arrows. You can also configure your IDLE. 8/28/

15 Can anything be a variable name? Answer: NO. You can use: Any letter Number, but not initially. ex: name1 is good, 1name is not Underscore "_". ex: student_name Variable names are case-sensitive! greet and Greet are two different variables. Following are built-in Python keywords and cannot be used as a variable name: and assert break class continue def del elif else except exec finally for from global if import in is lambda not or pass raise return try while yield 8/28/

16 Restarting shell Ctrl+F6 restarts IDLE shell >>> greet = 'Hello,' >>> nameis = 'my name is' >>> name = 'Homer' >>> print(greet, nameis, name) Hello, my name is Homer >>> name = 'Marge' >>> print(greet, nameis, name) Hello, my name is Marge ================================ RESTART ==================== >>> print(greet, nameis, name) Traceback (most recent call last): File "<pyshell#3>", line 1, in <module> print(greet, nameis, name) NameError: name 'greet' is not defined After RESTART, the 3 variables are no longer defined!! 8/28/

17 String vs. number: '+' and len() >>> >>> '4 + 15' '4 + 15' >>> '4' + '15' '415' >>> 'ab' + 'cde' 'abcde' >>> len('abcde') 5 >>> len('4' + '15') 3 >>> len('ab' + 'cde') 5 >>> len(4 + 15) Traceback (most recent call last): File "<pyshell#12>", line 1, in <module> len(4 + 15) TypeError: object of type 'int' has no len() 8/28/

18 String vs. number: '+' and len() >>> >>> '4 + 15' '4 + 15' >>> '4' + '15' '415' >>> 'ab' + 'cde' 'abcde' >>> len('abcde') 5 >>> len('4' + '15') 3 >>> len('ab' + 'cde') 5 >>> len(4 + 15) Traceback (most recent call last): File "<pyshell#12>", line 1, in <module> len(4 + 15) TypeError: object of type 'int' has no len() ERROR: Integers do not inherently have length! 8/28/

19 len() >>> >>> '4 + 15' '4 + 15' >>> '4' + '15' '415' >>> 'ab' + 'cde' 'abcde' >>> len('abcde') 5 >>> len('4' + '15') 3 >>> len('ab' + 'cde') 5 >>> len(4 + 15) len() returns the length of a string measured in # of characters Traceback (most recent call last): File "<pyshell#12>", line 1, in <module> len(4 + 15) TypeError: object of type 'int' has no len() 8/28/

20 +: number vs. string operation >>> >>> '4 + 15' '4 + 15' >>> '4' + '15' '415' >>> 'ab' + 'cde' 'abcde' >>> len('abcde') 5 >>> len('4' + '15') 3 >>> len('ab' + 'cde') 5 >>> len(4 + 15) 4 and 15 are integers. + is an addition operator '4' and '15' are strings of letters. + is a concatenation operator Traceback (most recent call last): File "<pyshell#12>", line 1, in <module> len(4 + 15) TypeError: object of type 'int' has no len() 8/28/

21 + vs. print >>> 'police' + 'man' 'policeman' >>> print('police', 'man') police man >>> print('police' + 'man') policeman 8/28/

22 + vs. print >>> 'police' + 'man' 'policeman' >>> print('police', 'man') police man >>> print('police' + 'man') policeman prints two strings, separated by a space prints the concatenated output as a single string 8/28/

23 +, *: overloaded operators >>> 14 * 3 42 >>> 'abc' * 3 'abcabcabc' >>> '14' * 3 '141414' >>> 'x' * 10 'xxxxxxxxxx' 8/28/

24 +, *: overloaded operators >>> 14 * 3 42 >>> 'abc' * 3 'abcabcabc' >>> '14' * 3 '141414' >>> 'x' * 10 'xxxxxxxxxx' Integers arguments. * is a multiplication operator String argument on left. * is a multi-copy concatenation operator Just like +, * also behaves differently for number and string arguments: overloaded operators 8/28/

25 + as concatenation operator >>> w1 = 'school' >>> w2 = 'bus' >>> w1+w2 'schoolbus' >>> print(w1, w2) school bus >>> print(w1+w2) schoolbus >>> w1+' '+w2 'school bus' >>> print(w1+' '+w2) school bus >>> [w1, w2] ['school', 'bus'] 8/28/

26 A list of strings >>> w1 = 'school' >>> w2 = 'bus' >>> w1+w2 'schoolbus' >>> print(w1, w2) school bus >>> print(w1+w2) schoolbus >>> w1+' '+w2 'school bus' >>> print(w1+' '+w2) school bus >>> [w1, w2] ['school', 'bus'] A list containing two strings. Square bracket [ ] marks the list data type. 8/28/

27 A string can contain a space >>> w1 = 'school' >>> w2 = 'bus' >>> w1+w2 'schoolbus' >>> print(w1, w2) school bus >>> print(w1+w2) schoolbus >>> w1+' '+w2 'school bus' >>> print(w1+' '+w2) school bus >>> [w1, w2] ['school', 'bus'] Concatenating two words with a space ' ' in between 8/28/

28 String String: a single piece of text, composed of a sequence of characters. Enclosed in ' ' or " " >>> print("it's me, Homer.") It's me, Homer. >>> print('homer says "hi."') Homer says "hi." 8/28/

29 String String: a single piece of text, composed of a sequence of characters. Enclosed in ' ' or " " >>> print("it's me, Homer.") It's me, Homer. >>> print('homer says "hi."') Homer says "hi." Enclosed in """ """ (triple double quotes) Can be multi-line! >>> print("""this is a long string that spans three lines.""") This is a long string that spans three lines. 8/28/

30 The trouble with quotation marks But how to print: >>> print("""both ' and " are ok.""") Both ' and " are ok. Method 1: Use triple double quotes """. >>> print("""both ' and " are ok.""") Both ' and " are ok. Method 2: Use backslash \ to "escape". >>> print('both \' and " are ok.') Both ' and " are ok. >>> print("both ' and \" are ok.") Both ' and " are ok.? 8/28/

31 Escaping with backslash \ >>> print('it\'s snowing.') It's snowing. >>> print('lala\tlala') lala lala >>> print('lala\nlala') lala lala >>> multi = """This is a long string across multiple lines.""" >>> print(multi) This is a long string across multiple lines. >>> multi 'This is a\nlong string across\nmultiple lines.' 8/28/

32 Escaping with backslash \ >>> print('it\'s snowing.') It's snowing. >>> print('lala\tlala') lala lala >>> print('lala\nlala') lala lala >>> multi = """This is a long string across multiple lines.""" >>> print(multi) This is a long string across multiple lines. >>> multi 'This is a\nlong string across\nmultiple lines.' 8/28/

33 Special character and \ Prefixing backslash \ (=escaping) turns: A special character into a normal one SPECIAL NORMAL ' String delimiter \' Single quote character " String delimiter \" Double quote character \ Escape marker \\ Backslash character A normal character into a special one NORMAL SPECIAL n Alphabet n \n New line character t Alphabet t \t Tab character 8/28/

34 Practice 2 minutes Compose print commands to output the following: >>> print('look in C:\\temp\\note.') Look in C:\temp\note. >>> print('lisa said \'Look in C:\\temp\\note\'.') Lisa said 'Look in C:\temp\note'. >>> print('lisa said \'Look in C:\\temp\\note and find "my.txt".\'') Lisa said 'Look in C:\temp\note and find "my.txt"'. >>> print('roses are red,\nviolets are blue,\nsugar is sweet.') Roses are red, Violets are blue, Sugar is sweet. 8/28/

35 Practice 2 minutes Compose print commands to output the following: >>> print('look in C:\\temp\\note.') Look in C:\temp\note. >>> print('lisa said \'Look in C:\\temp\\note\'.') Lisa said 'Look in C:\temp\note'. >>> print('lisa said \'Look in C:\\temp\\note and find "my.txt".\'') Lisa said 'Look in C:\temp\note and find "my.txt"'. >>> print('roses are red,\nviolets are blue,\nsugar is sweet.') Roses are red, Violets are blue, Sugar is sweet. 8/28/

36 Wrap-up Exercise #1 Review today's lesson Learn on your own: String Methods 1, Boolean Operators Due 30 mins before next class (=Thu 4pm) Friday recitation Will send individual tomorrow. Python installation/configuration: make sure you followed all instructions in "Getting Started" sections Next class More Python practice Study Tutorials 5, 7, 16, 17, 18 and Additional Topics 1, 2, 3 before class New to programming? Try to log a few additional hours! 8/28/