Python Code Snippets and Programming Concepts

Posted on Dec 1, 2024 in Computers

HW9: Shift String

Function caesar shifts letters in a string:

def caesar(left, shift): 
    ref = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" 
    con = "" 
    letf = left.strip().upper() 
    for x in range(0, len(left)): 
        if letf[x] not in ref: 
            con += letf[x] 
        else: 
            con += ref[(ref.find(left[x]) + shift) % 26] 
    return con 

CW10: Recursion

Function fib calculates Fibonacci numbers recursively:

def fib(n): 
    if n in [1, 2]: 
        return 1 
    else: 
        return fib(n - 1) + fib(n - 2) 

Note: The original code had a typo (n+1) and would cause an infinite loop. It should be (n-2). Use Ctrl + C to stop infinite loops.

HW10: Syntax and Runtime Errors

Syntax Errors

Example of syntax errors.

Runtime Errors

Example of runtime errors (e.g., variable not defined).

Logic Errors

Example of logic errors (e.g., missing parenthesis).

CW11: Classes

Employee Class

class Employee: 
    def __init__(self, first, last): 
        self.first = first 
        self.last = last 
    def initial(self): 
        return self.first[0] + self.last[0] 
    def number_letter(self): 
        return len(self.first) + len(self.last) 

Executive Class (Inheritance)

class Executive(Employee): 
    def __init__(self, first, last, salary, term): 
        super().__init__(first, last) 
        self.salary = salary 
        self.term = term 
    def pv_salary(self): 
        pv = round(sum([self.salary / 1.005 ** i for i in range(1, self.term + 1)])) 
        return f"The present value of {self.first} {self.last}'s {self.term} months of salaries is ${pv}." 

Set Operations

• {1, 2, 5}.union({2, 3, 5}) >> {1, 2, 3, 5}
• {1, 2, 5}.intersection({2, 3, 5}) >> {2, 5}
• {2, 3}.symmetric_difference({2, 4, 5}) >> {3, 4, 5}
• {2, 3} - {2, 4, 5} >> {3}

Built-in functions: max(list), min(list), sum(list)

CW12: File Handling – First Letters

def first_letters(file): 
    with open(file, 'r') as infile: 
        lst = [line[0] for line in infile] 
    return ''.join(lst) 

HW13: Set Union from Files

with open("bank1.txt", "r") as infile: 
    set1 = set() 
with open("bank2.txt", 'r') as infile: 
    table = [line.strip().replace(' ', ',').split(',') for line in infile] 
for x in table: 
    x[-1], x[-2] = x[-2], x[-1] 
set2 = {','.join(x) + "\n" for x in table} 
merged = sorted(set1.union(set2)) 
with open("bank_merged.txt", 'w') as outfile: 
    outfile.writelines(merged) 

HW12: People Names – Initials

with open("people.txt", 'r') as infile: 
    table = [line.split() for line in infile] 
    mixed = sorted([x[0][0] + x[1][0] for x in table]) 
with open("inital.txt", 'w') as outfile: 
    outfile.writelines("\n".join(mixed)) 

Recursion – Sum Up

def recur_sum(lst): 
    if len(lst) == 0: 
        return 0 
    else: 
        return lst[0] + recur_sum(lst[1:]) 

File – First Letter

def first_letter(file): 
    with open(file, 'r') as infile: 
        lst = [line[0] for line in infile] 
    return ''.join(lst) 

Caesar Cipher Function

def casear(message, action, shift): 
    ref = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" 
    converted = "" 
    for x in message.upper().replace(" ", ''): 
        if action == 'E': 
            converted += ref[(ref.find(x) + shift) % 26] 
        elif action == "D": 
            converted += ref[(ref.find(x) - shift) % 26] 
    return converted 

Note: The original code had a typo in the decryption part. It should be (ref.find(x) – shift) % 26.

Prime Factorization

def factorization(n): 
    lst = [] 
    for i in range(2, n): 
        if n % i == 0: 
            j = 0 
            while n % i == 0: 
                j += 1 
                n /= i 
            lst.append((i, j)) 
    return lst 

HW4: Matrix Operations

matrix = eval(input("Enter")) 
a = matrix[0] 
b = matrix[1] 
c = matrix[2] 
d = matrix[3] 
det = a * d - b * c 
inverse = [[d / det, -b / det], [-c / det, a / det]] 
print(inverse) 

Note: The input is expected to be a tuple like (1,2,3,4).