Standard 2

Dearest item

items is a non-empty list of (name, price) tuples. Write dearest(items) that returns the name of the most expensive one.

dearest([("milk", 2.5), ("apple", 40), ("bread", 25)])  ->  "apple"

def dearest(items):
    ...

Running total

Write running(amounts) that returns a list where each position holds the sum of all amounts up to and including that one.

running([10, 5, 20])  ->  [10, 15, 35]
running([])           ->  []

def running(amounts):
    ...

Split a product code

Product codes look like BRD-001-A: department, number and batch separated by dashes. Write parts(code) that returns the three pieces as a tuple.

parts("BRD-001-A")  ->  ("BRD", "001", "A")

def parts(code):
    ...

Pop several

Write pop_n(stack, n) that pops up to n items off a stack (a list) and returns them as a list in the order they were popped. Stop early if the stack runs out.

pop_n(["a", "b", "c"], 2)  ->  ["c", "b"]     (stack is now ["a"])
pop_n(["a"], 3)            ->  ["a"]

def pop_n(stack, n):
    ...

Discounted total

Orders of 100 or more get 20% off, orders of 50 or more get 10% off, smaller orders pay full price. Write to_pay(total) that returns the amount to pay, rounded to two decimal places.

to_pay(120)    ->  96.0
to_pay(60)     ->  54.0
to_pay(77.77)  ->  69.99
to_pay(20)     ->  20      (20.0 is fine too)

def to_pay(total):
    ...

Codes to names

codes maps item names to product codes, and no two items share a code. Write by_code(codes) that returns the reverse mapping, from code to name.

by_code({"bread": "BRD-001", "milk": "MLK-010"})  ->  {"BRD-001": "bread", "MLK-010": "milk"}

def by_code(codes):
    ...

Word counts

Write word_counts(text) that returns a dictionary of how many times each word appears, treating capitals and lowercase as the same word.

word_counts("Bread and milk and bread")  ->  {"bread": 2, "and": 2, "milk": 1}

def word_counts(text):
    ...

Common prefix

Write common_prefix(a, b) that returns the longest string that both a and b start with.

common_prefix("sourdough", "soup")  ->  "sou"
common_prefix("milk", "bread")      ->  ""

def common_prefix(a, b):
    ...

Two largest

Write top_two(prices) that returns the two largest values from a list of at least two, largest first, using heapq. A repeated value counts each time it appears.

top_two([40, 25, 2.5, 60])  ->  [60, 40]
top_two([5, 5, 1])          ->  [5, 5]

import heapq

def top_two(prices):
    ...

Pair them up

Write pairs(items) that groups a list with an even number of items into consecutive pairs, as a list of tuples.

pairs(["a", "b", "c", "d"])  ->  [("a", "b"), ("c", "d")]
pairs([])                    ->  []

def pairs(items):
    ...

Next: Standard 3.