CS Introduction to Programming Fall 2016

Transcription

1 CS Introduction to Programming Fall 2016 Exam 3 Review - Part 2 (Python) Friday, December 2 nd, 2016 Ahmed Ibrahim 1 / 26

2 Course Evaluation Please take a few minutes to submit your course evaluation on Collab 2 / 26

3 Touch-up Alexander s office hours are on Sunday 2-5. Any problems with using py in MATLAB, Piazza. P3 is due by the end of Monday 12/5. 3 / 26

4 About the Test Thursday, December 2, Your lecture hall (Thornton E316). Time: 3 hours (9:00AM - 12:00PM). Format: writing on paper; bring pen/pencil (nothing else). Bubble your first page (2 points). 4 / 26

5 About the Test Students with accommodations should contact the SDAC to schedule a time slot any time on Wednesday to take the test. There is Office Hours on Monday and Tuesday. No Office Hours will be held on Wednesday. (You can still and we ll figure something out) Be here early! 5 / 26

6 What is on the Test Python: Arithmetic / Boolean / Strings / Expression Evaluation / Conditions / Loops (while / for) / Functions / Lists Call-by-value / Call-by-reference / Files / etc (NO DICTIONARIES / RANDOM / Input Validation) MATLAB: Arithmetic / Boolean / Strings / Expression Evaluation / Conditions / Loops (while / for) / Spacing / Functions Multiple Output / etc (Simple Plotting) 6 / 26

7 Type of Questions True / False (Python & MATLAB) Multiple Choice (Python & MATLAB) Expression Evaluation (Python & MATLAB) Short Answer & Tracing (Python & MATLAB) Writing functions (Python & MATLAB) One big coding question (!?) 7 / 26

8 Questions? 8 / 26

9 Remember The algorithm must be: - Unambiguous - Executable - Terminating Control Structures: sequence / condition / loop / subprogram Types of Errors: Syntax / Logical / Runtime 9 / 26

10 Strings The split() method: fn, ln = input("please enter your name: ").split() name_list = input("please enter your name: ").split() String indexes: str = "Welcome to CS1113!" what is str[3]? what is str[-1]? what is str[len(str)-1]? what is str[ : 5]? what is str[3:7]? what is str[11 : ]? 10 / 26

11 String Replication / Concatenation String Replication: str = "10" * 3 # "101010" String Concatenation: str = "10" + "3" # "103" String Length: len(str) # GETS THE LENGHT OF THE STRING 11 / 26

12 Boolean Operators Evaluate the following expressions: 50 == 50 0 < temp < > 2 and not ( 7 > 5 ) 6 > 2 or not ( 7 < 5 ) 12 / 26

13 Functions Simpler code Code reuse Write the code once and call it multiple times Better testing and debugging Faster development Easier facilitation of teamwork 13 / 26

14 Functions Can have 0 or more arguments Number of parameters passed MUST be the same as the number of args - unless arguments are optional! Can have 0, 1 or multiple return values Local variables can t be accessed outside the function 14 / 26

15 Functions A function starts with a header def function_name (0_or_more_arguments): # code # x = 10 -> local variable # code # return statement # code 15 / 26

16 Pass by Value / 26

17 Pass by Reference / 26

18 Lists # 1: Creating a list values = [32, 54, 67.5, 29, 35, 80, 115, 44.5, 100, 65] # 2: Accessing a list element values[5] = / 26

19 Out of Range Errors Perhaps the most common error in using lists is accessing a nonexistent element values = [2.3, 4.5, 7.2, 1.0, 12.2, 9.0, 15.2, 0.5] values[8] = 5.4 # Error values has 8 elements, # and the index can range from 0 to 7 If your program accesses a list through an out-of-range index, the program will generate an exception at run time. 19 / 26

20 List Concatenation The concatenation of two lists is a new list that contains the elements of the first list, followed by the elements of the second myfriends = ["Fritz", "Cindy"] yourfriends = ["Lee", "Pat", "Phuong"] Two lists can be concatenated by using the plus (+) operator: ourfriends = myfriends + yourfriends # Sets ourfriends to ["Fritz", "Cindy", "Lee", "Pat","Phuong"] 20 / 26

21 List Replication Replication of two lists is a new list that contains the elements of the first list, followed by the elements of the second. month_in_quarter = [1, 2, 3] * 4 Results in the list [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2,3] The integer specifies how many copies of the list should be concatenated One common use of replication is to initialize a list with a fixed value monthly_scores = [0] * / 26

22 Looping Over the List Given a list that contains n elements, you can loop over the list using one of the following ways: # list index used for i in range(len(values)) : print(i, values[i]) # index values not needed (traverse list elements) for element in values : print(element) 22 / 26

23 Loop Over a Table table = [ [3,4,5], [6,7], [8,9,10,11,12] ] for row in range( len(table) ): for column in range( len(table[row]) ): print( table[row][column] ) 23 / 26

24 Reading From a File - for infile = open("input.txt", "r") for line in infile : # Process the line. infile.close() 24 / 26

25 Writing to a File To open a file for writing, you provide the name of the file as the first argument to the open function and the string "w" as the second argument: outfile = open("output.txt", "w") outfile.write("text\n") #string only If the output file already exists, it is emptied before the new data is written into it If the file does not exist, an empty file is created 25 / 26

26 Practice Coding on Paper How to practice? Try re-solving the Homeworks and Lab problems on paper without looking at your code or textbook. Try re-solving the lecture code on paper without looking at your notes or the lecture slides. Start with: HW4 / HW5 / HW6 / HW7 / HW8 / Lab8 / Lab10 26 / 26