Week 6 - Python

Welcome to CS50 again! This blog will contain my review for Week 6's content about Python.

Lecture

1. Nothing much to note down.

Section

1. Nothing to note down. Try yourself and read the document is quite helpful.

Shorts

1. Not much to note down. Just introduction to Python.

Problem Set 6

C-to-Python-Sentimental

Nothing to say

DNA

Divide and Conquer

DNA Algorithm:
1. Check for command-line usage
2. Read database file into a variable
3. Read sequence file into a variable
4. Find longest match of each STR in DNA sequence
5. Check database for matching profiles

Useful Snippets

1. Check for command-line uasge

if not len(sys.argv) == 3:
    print("error")
    return

1. Read database file into a variable

rows = []
with open(sys.argv[1]) as file:
    reader = csv.DictReader(file)
    for row in reader:
        rows.append(row)

1. Read DNA sequence file into a variable

with open(sys.argv[2]) as file:
    sequence = file.read()

1. Find longest match of each STR in DNA sequence

result = {}
for STR in STRs:
    count = longest_match(sequence, STR)
    result[STR] = f"{count}"

1. Check database for matching profiles

for row in rows:
    name = row.pop("name")
    if row == result:
        print(name)
        break
else:
    print("No match.")

Take-aways

1. The command-line arguments are stored in sys.argv, which is a list. The first argument, which is sys.argv[0] is the script's name and the arguments after this are the actual arguments.

2. Using this code to read from the file,

with open("filename") as file:
    content = file.read()

The variable content can be accessed outside the with statement.

3. The == can be used to determine whether two dictionaries are equivalent or not. 4. To pop a specific key:value pair from the dictionary,

temp = dict.pop(key)`.  

1. To add add a key:value pair to the dictionary,

dict = {}
dict[key] = value

Lecture - Week6.5

1. In reinforcement learning, if the agent does well, you give them a reward, otherwise, punish them.