Fall 2020 Berkeley cs61a hw04答案

def make_bank(balance):"""Returns a bank function with a starting balance. Supportswithdrawals and deposits.>>> bank = make_bank(100)>>> bank('withdraw', 40)    # 100 - 4060>>> bank('hello', 500)      # Invalid message passed in'Invalid message'>>> bank('deposit', 20)     # 60 + 2080>>> bank('withdraw', 90)    # 80 - 90; not enough money'Insufficient funds'>>> bank('deposit', 100)    # 80 + 100180>>> bank('goodbye', 0)      # Invalid message passed in'Invalid message'>>> bank('withdraw', 60)    # 180 - 60120"""def bank(message, amount):"*** YOUR CODE HERE ***"nonlocal balanceif message == 'withdraw':if amount > balance:return 'Insufficient funds'balance = balance - amountelif message == 'deposit':balance = balance + amountelse:return 'Invalid message'return balancereturn bankdef make_withdraw(balance, password):"""Return a password-protected withdraw function.>>> w = make_withdraw(100, 'hax0r')>>> w(25, 'hax0r')75>>> error = w(90, 'hax0r')>>> error'Insufficient funds'>>> error = w(25, 'hwat')>>> error'Incorrect password'>>> new_bal = w(25, 'hax0r')>>> new_bal50>>> w(75, 'a')'Incorrect password'>>> w(10, 'hax0r')40>>> w(20, 'n00b')'Incorrect password'>>> w(10, 'hax0r')"Frozen account. Attempts: ['hwat', 'a', 'n00b']">>> w(10, 'l33t')"Frozen account. Attempts: ['hwat', 'a', 'n00b']">>> type(w(10, 'l33t')) == strTrue""""*** YOUR CODE HERE ***"wrong_trail_password = []wrong_trail_times = 0def withdraw(amount, trail_password):nonlocal balance, wrong_trail_timesif wrong_trail_times == 3:return "Frozen account. Attempts: " + str(wrong_trail_password)if password == trail_password:if amount > balance:return 'Insufficient funds'balance = balance - amountreturn balanceelse:wrong_trail_times += 1if wrong_trail_times <= 3:wrong_trail_password.append(trail_password)return 'Incorrect password'return withdrawdef repeated(t, k):"""Return the first value in iterator T that appears K times in a row. Iterate through the items such thatif the same iterator is passed into repeated twice, it continues in the second call at the point it left offin the first.>>> s = iter([10, 9, 10, 9, 9, 10, 8, 8, 8, 7])>>> repeated(s, 2)9>>> s2 = iter([10, 9, 10, 9, 9, 10, 8, 8, 8, 7])>>> repeated(s2, 3)8>>> s = iter([3, 2, 2, 2, 1, 2, 1, 4, 4, 5, 5, 5])>>> repeated(s, 3)2>>> repeated(s, 3)5>>> s2 = iter([4, 1, 6, 6, 7, 7, 8, 8, 2, 2, 2, 5])>>> repeated(s2, 3)2"""assert k > 1"*** YOUR CODE HERE ***"count = 1current_number = next(t)next_number = next(t)while True:if current_number == next_number:count += 1if count == k:return next_numbercurrent_number, next_number = next_number, next(t)else:count = 1current_number, next_number = next_number, next(t)
def permutations(seq):"""Generates all permutations of the given sequence. Each permutation is alist of the elements in SEQ in a different order. The permutations may beyielded in any order.>>> perms = permutations([100])>>> type(perms)<class 'generator'>>>> next(perms)[100]>>> try: #this piece of code prints "No more permutations!" if calling next would cause an error...     next(perms)... except StopIteration:...     print('No more permutations!')No more permutations!>>> sorted(permutations([1, 2, 3])) # Returns a sorted list containing elements of the generator[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]>>> sorted(permutations((10, 20, 30)))[[10, 20, 30], [10, 30, 20], [20, 10, 30], [20, 30, 10], [30, 10, 20], [30, 20, 10]]>>> sorted(permutations("ab"))[['a', 'b'], ['b', 'a']]""""*** YOUR CODE HERE ***"if len(seq) == 1:yield seqelse:for element in permutations([x for x in seq if x != seq[0]]):for k in range(len(element) + 1):yield element[:k] + [seq[0]] + element[k:]def make_joint(withdraw, old_pass, new_pass):"""Return a password-protected withdraw function that has joint access tothe balance of withdraw.>>> w = make_withdraw(100, 'hax0r')>>> w(25, 'hax0r')75>>> make_joint(w, 'my', 'secret')'Incorrect password'>>> j = make_joint(w, 'hax0r', 'secret')>>> w(25, 'secret')'Incorrect password'>>> j(25, 'secret')50>>> j(25, 'hax0r')25>>> j(100, 'secret')'Insufficient funds'>>> j2 = make_joint(j, 'secret', 'code')>>> j2(5, 'code')20>>> j2(5, 'secret')15>>> j2(5, 'hax0r')10>>> j2(25, 'password')'Incorrect password'>>> j2(5, 'secret')"Frozen account. Attempts: ['my', 'secret', 'password']">>> j(5, 'secret')"Frozen account. Attempts: ['my', 'secret', 'password']">>> w(5, 'hax0r')"Frozen account. Attempts: ['my', 'secret', 'password']">>> make_joint(w, 'hax0r', 'hello')"Frozen account. Attempts: ['my', 'secret', 'password']"""""*** YOUR CODE HERE ***"def remainders_generator(m):"""Yields m generators. The ith yielded generator yields natural numbers whoseremainder is i when divided by m.>>> import types>>> [isinstance(gen, types.GeneratorType) for gen in remainders_generator(5)][True, True, True, True, True]>>> remainders_four = remainders_generator(4)>>> for i in range(4):...     print("First 3 natural numbers with remainder {0} when divided by 4:".format(i))...     gen = next(remainders_four)...     for _ in range(3):...         print(next(gen))First 3 natural numbers with remainder 0 when divided by 4:4812First 3 natural numbers with remainder 1 when divided by 4:159First 3 natural numbers with remainder 2 when divided by 4:2610First 3 natural numbers with remainder 3 when divided by 4:3711""""*** YOUR CODE HERE ***"def naturals():"""A generator function that yields the infinite sequence of naturalnumbers, starting at 1.>>> m = naturals()>>> type(m)<class 'generator'>>>> [next(m) for _ in range(10)][1, 2, 3, 4, 5, 6, 7, 8, 9, 10]"""i = 1while True:yield ii += 1

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Fall 2020 Berkeley cs61a hw04答案

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