Lec19

Lec19, Mon 03/09

Review

Algorithm: a solution to a problem, typically written in a human-understandable language(pseudocode)
Pay attention to conditionals!
You can find the list of the UCSB major/minor codes here: https://registrar.sa.ucsb.edu/faculty-staff/resources-for-faculty-staff/major-minor-codes

ucsb_majors = {}
try:
  infile = open("major_codes.txt")
except:
  print("This files does not exist.")
  print("ERROR:", err)
else:
  for line in infile:
    # line = line.split('\t').strip() #strip the white space
    line_to_write = line
    line = line.strip() # remove white psace
    line = line.split('\t')
    # print("Key = ", line[0].strip())
    key = line[0].strip() # make sure there's no extra white space
    # ucsb_majors[key] = line[1]
    if ucsb_majors.get(key) != None:
      print(line)
      ucsb_majors[key] = line[1]
      continue
    else:
      outfile.write(line_to_write)
    
    print(line)
infile.close()
outfile.close()

What is Computer Science?

What is the other component of Computer Science?

Pseudo code!

gives the “algorithm”: sequence of steps to solve a problem

Roadmap

What are the basic elements of programming?

Pseudocode/Algorithm
Basic Data Types
- This forces you to care about syntax!
- int and float
  - Allow you to do arithmetic ==> +, -, **, //, /, %, *
- bool
  - if/else/elif
    - == and !=
  - Flow of elements
- string
  - Indexing
  - len and print
Functions!
- Parameters
  - The name I have in a parameter is different than what I actually use inside the function
- These will be a huge component on the final exam….
- pytest, assert
  - Verifies the correctness of code
More complex data types
- Lists
  - len and indexing now apply to lists
  - plot (not going to be on the exam)
- Tuples
  - Mutability
  - Named tuples
    - Will definitely be on the final!! Indexing gave us…
Loops!
- while loop
  - range()
- for loop
  - Anything you can do with a while loop you can do with a for loop (without infinite loops)!
Recursion
- Call our function within its definition
Dictionaries
- Will definitely be on the final!!
File I/O
- Reading in our data to store complex data types
- Writing out files into a file

Consider making a similar concept map while studying!

Practice Algorithm

Exceptions won’t be on the exam, but it’s still good to know for your future projects.

We can use try to tell python that a line of code may cause an error. This prevents your code from crashing, giving you a way to gracefully handle the exception.

For example,

try:
    infile = open("major_codes.txt")
except FileNotFoundError as err:
    print("No such file exists.")
    print("ERROR:", err) 
else:
    ucsb_majors = {}
    for line in infile: # line is a str
        line = line.strip() # strips whitespaces from the beginning and end of line
        line = line.split('\t') # splits at the whitespace
        print(line)
        key = line[0].strip() # strips whitespaces from the key
        value = line[1]
        ucsb_majors[key] = value
    infile.close()

Reading a large file in may take a really long time to load, and will make testing your function very tedious….

Instead, consider using a small file for testing to speed up the process and use the large file when your function is ready.

Note! Even if you are not submitting the replacement lab, we still encourage you to look at it for practice! Knowing how to compute summary statistics yourself might come in handy during the final.

Let’s fix our code to skip duplicates.

try:
    infile = open("major_codes.txt")
except FileNotFoundError as err:
    print("No such file exists.")
    print("ERROR:", err) 
else:
    ucsb_majors = {}
    for line in infile: # line is a str
        line = line.strip() # strips whitespaces from the beginning and end of line
        line = line.split('\t') # splits at the whitespace
        print(line)
        key = line[0].strip() # strips whitespaces from the key
        value = line[1]
        if ucsb_majors.get(key) != None:
            ucsb_majors[key] = value
            print(type(line))
            outfile.write(line_to_write)
    infile.close()

Practice your debugging skills: given a function/code that is not correct, find the error or where it might potentially be going wrong.

Final file after Lecture on Monday

ucsb_majors = {}

outfile = open("major-codes-2-clean.txt", 'w')
try:
    infile = open("major-codes-2.txt")
except FileNotFoundError as err:
    print("This file does not exist.")
    print("ERROR:", err)
else:
    for line in infile:
        line_to_write = line
        line = line.strip()
        line = line.split('\t')
        #print("Key =", line[0].strip())
        key = line[0].strip()
        #ucsb_majors[key] = line[1]
        print(ucsb_majors.get(key))
        if ucsb_majors.get(key) == None:
            print(line)
            ucsb_majors[key] = line[1]
            continue
        else:
            outfile.write(line_to_write)
            #outfile.write(line)
        
        
        
    infile.close()
outfile.close()

Final file after Lecture on Tuesday

outfile = open("major_codes_clean.txt", 'w')

try:
    infile = open("major-codes-2.txt", 'r')
    #infile = open("major-codes.txt")
except FileNotFoundError as err:
    print("No such file exists.")
    print("ERROR:", err)
else:
    ucsb_majors = {}
    for line in infile: # line is a str
        #print("'", line, "'", sep="")
        line_to_write = line
        line = line.strip()
        line = line.split('\t')
        print(line)
        key = line[0].strip()
        value = line[1]
        if ucsb_majors.get(key) != None:
            ucsb_majors[key] = value
            print(type(line))
            outfile.write(line_to_write)
        else:
            # we found a duplicate
            pass
    infile.close()

outfile.close()