cs2370 Notes: 06 Design With Lists

Designing a function: #

Purpose statement
Signature (e.g. int -> int)
Examples
Stub
Standard pattern
Write the body
Asserts

Designing a None function

Print a square of a given size with “+-|” characters.

Signature: int -> None

# Print a square with interior size as provided
def print_square(size):
    print "+" + (size * "-") + "+"
    for ii in range(0, size):
        print "|" + (size * " ") + "|"
    print "+" + (size * "-") + "+"

Lists

A list in Python is the standard way of handling a sequence of 0 or more items.

Basic operations:

for / in loop
Indexing
Slicing
.append
concat with +

max_val

Design a function that finds the maximum value in a list.

Standard pattern:

# [number] -> number
def max_val(xs):
    y = 0
    
    for x in xs:
        pass
        
    return y

Problem: Negative numbers, solution: xs[0]

Problem: Empty list, solutions:

None
Throw

contains

Design a function that determines if an integer appears in a list.

Standard pattern:

# [int], int -> bool
def contains(xs, y):
    for x in xs:
        ... something with y... 
    return True # or False

add1_to_all

# [number] -> [number]
def add1_to_all(xs):
    ys = []
    for x in xs:
        ys.append(x + 1)
    return ys

# [number] -> None
def add1_to_each(xs):
    for ii in range(0, len(xs)):
        xs[ii] =

insertion sort

Pattern gives us:

# [number] -> [number]
def sort(xs):
    ys = []
    
    for x in xs:
        ys = insert(ys, x)

    return ys

# We need a helper

# [number], number -> [number]
def insert(xs, y):
    lt = []
    gt = []
   
    for x in xs:
        if x <= y:
            lt.append(x)
        elif x > y:
            gt.append(x)
    
    return lt + [y] + gt