猴子學Python - Business Computing in Python (week 4)

Conditionals

1. Nested if-else

   if XXX: if YYY: statement A else: statement B else: statement C

2. Avoid potential inconsistency
   Don’t repeat, don’t copy paste your code.
   Eliminate redundancy!

3. Ternary if operator

   min = a if a <= c else c

   • parentheses are helpful. They make the code more readable.

     min = (a if (a <= c) else c)

4. else if = elif

   if XXX: elif YYY: else:

5. Logical operators

   • ‘and’, ‘or’, ‘not’
   • operators have precedence rule, but don’t memorize it. Just use PARENTHESES!
   • conditions must be complete at both sides.
   • ‘not’ is a unary operator.

Iterations(loop)

1. ‘while’

   • an ‘if’ that repeats
   • use ‘loop counters’ to keep track of/update the loop. Self assignment are useful (+=)
   • logical error may create infinite loops

2. ‘break’ and ‘continue’

   • ‘break’ will exit the loop immediately.
   • ‘continue’ will skip the statements in the loop and recheck the looping condition.
   • ‘break’ gives a loop multiple exits, it sometimes makes the code harder to read.

3. ‘for’

   • for variable in list
     variable: the loop counter
     list: variables that will be traersed.
   • how to create list?
   • range() function

4. biggest difference between ‘while’ and ‘for’
   the statement after ‘while’ is a condition but the statement after ‘for’ is just a counter assignment

5. Nested loops

   • helpful for multi-dimentional cases.
   • print(xxxxxxx , end = “ “) the end is used to add anything you want at the end of the printed Chars without adding a new line.

Precision

1. useing 'math' module

2. most decimal fractional numbers can only be approximated!!

3. use imprecise comparisons but can't 100% solve the problem.

Exercise

Newsvendor problem

c = int(input("perchase cost"))
r = int(input("price"))
N = int(input("needs")) + 1
q = int(input("perchase ammount"))

totalprof = 0
totalpercentage = 0
if q == 0:
    print("nothing!")

else:
    for j in range(0, q + 1):
        if j < q:
            pi = input("probability") 
            totalpercentage += pi
        else:
            pi = 100 - totalpercentage
        print(totalpercentage)
        print(pi)
        profit = (r * j - q * c) * pi
        totalprof += profit
        print(profit)
        print(totalprof)
        
print(totalprof)

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• Programming
• Python