Python Overiew - Department of Computer Science ...

Python Overiew

1. In the boxes below, fill in the missing code that will make the function definition match its description.

def every_nth_character(s, n): """ (str, int) -> str

Precondition: n > 0

Return a string that contains every nth character from s, starting at index 0.

>>> every_nth_character('Computer Science', 3) 'CpeSee'

"""

result = '' i=0

while

:

result = result + s[i]

i=

return result

2. Complete the examples in the docstring and then the function body.

def count_uppercase(s): """ (str) -> int

Return the number of uppercase letters in s.

"""

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3. In math, the Collatz conjecture states that starting from any positive integer, you will eventually reach the number 1 by repeatedly applying the following two rules: ? if the number is even, divide it by 2 to get the next number in the sequence ? if the number is odd, multiply by 3 and add 1 to get the next number in the sequence Repeatedly applying the rules generates a sequence of numbers. The Collatz step count is the number of applications of the rules required before the sequence reaches 1. For example, there are 8 Collatz steps in the Collatz sequence: n = 6 -> n = 3 -> n = 10 -> n = 5 -> n = 16 -> n = 8 -> n = 4 -> n = 2 -> n = 1 Complete this function to count the Collatz steps for a particular number n.

def count_collatz_steps(n): """ (int) -> int

Precondition: n >= 1

Return the number of steps it takes to reach 1 by applying the two rules of the Collatz conjecture beginning from the positive integer n.

>>> count_collatz_steps(6) 8 """

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4. Complete the function body. def greatest_difference(nums1, nums2): """ (list of number, list of number) -> number Precondition: len(nums1) == len(nums2) and nums1 != [] Return the greatest absolute difference between numbers at corresponding positions in nums1 and nums2. >>> greatest_difference([1, 2, 3], [6, 8, 10]) 7 >>> greatest_difference([1, -2, 3], [-6, 8, 10]) 10 """

5. Complete the function body. def can_pay_with_two_coins(denoms, amount): """ (list of int, int) -> bool Return True if and only if it is possible to form amount, which is a number of cents, using exactly two coins, which can be of any of the denominations in denoms. >>> can_pay_with_two_coins([1, 5, 10, 25], 35) True >>> can_pay_with_two_coins([1, 5, 10, 25], 20) True >>> can_pay_with_two_coins([1, 5, 10, 25], 12) False """

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6. The express checkout is for grocery orders with 8 or fewer items. Complete the function body. def express_checkout(product_to_quantity): """ (dict of {str: int}) -> bool

Return True iff the grocery order in product_to_quantity qualifies for the express checkout. product_to_quantity maps products to the numbers of those items in the grocery order.

>>> express_checkout({'banana': 3, 'soy milk': 1, 'peanut butter': 1}) True >>> express_checkout({'banana': 3, 'soy milk': 1, 'twinkie': 5}) False """

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7. The Event class can be used to keep track of event related information, such name and start and end times. Implement the missing method bodies .

class Event: """A new calendar event."""

def __init__(self, start_time, end_time, event_name): """ (Event, int, int, str) -> NoneType

Precondition: 0 > e = Event(12, 13, 'Lunch') >>> e.start_time 12 >>> e.end_time 13 >>> e.name 'Lunch' """

def duration(self): """ (Event) -> int

Return the duration of this event. >>> e = Event(10, 11, 'Lecture') >>> e.duration() 1 """

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def __str__(self): """ (Event) -> str Return a string representation of this event. >>> e = Event(6, 7, 'Run') >>> str(e) 'Run: from 6 to 7' """

def __eq__(self, other): """ (Event, Event) -> bool Return True iff this event has the same start time, end time, and name as other. >>> e1 = Event(6, 7, 'Run') >>> >>>

"""

def overlaps(self, other): """ (Event, Event) -> bool Return True iff this event overlaps with event other. >>> e1 = Event(6, 7, 'Run') >>> e2 = Event(0, 7, 'Sleep') >>>

"""

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8. The Day class can be used to keep track of a set of events scheduled in a given date. Implement the missing method bodies .

import event

class Day: """A calendar day and its events."""

def __init__(self, day, month, year): """ (Day, int, str, int) -> NoneType

Initialize a day on the calendar with day, month and year, and no events.

>>> d = Day(30, 'November', 2016) >>> d.day 30 >>> d.month 'November' >>> d.year 2016 >>> d.events [] """

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def schedule_event(self, new_event): """ (Day, Event) -> bool

Attempts to schedule new_event on this day. If the event overlaps with an existing event return False without appending event. Otherwise, return True and append new_event.

>>> d = Day(1, 'December', 2016) >>> e = event.Event(11, 13, 'Meeting') >>> d.schedule_event(e) True >>> d.events[0] == e True >>> e2 = event.Event(11, 12, 'Lunch') >>> d.schedule_event(e2) False >>> e2 in d.events == False True """

def __str__(self): """ (Day) -> str

Return a string representation of this day.

>>> d = Day(29, 'November', 2016) >>> d.schedule_event(event.Event(15, 16, 'Submit A3 work')) True >>> d.schedule_event(event.Event(16, 23, 'Celebrate!')) True >>> print(d) 29 November 2016: - Submit A3 work: from 15 to 16 - Celebrate!: from 16 to 23 """

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