Exercises¶

1. Create a list containing 100 random integers between 0 and 1000 (use iteration, append, and the random module). Write a function called average that will take the list as a parameter and return the average.

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   (ex_9_4)

2. • Question
   • Answer

   Write a Python function that will take a the list of 100 random integers between 0 and 1000 and return the maximum value. (Note: there is a builtin function named max but pretend you cannot use it.)

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   (ex_9_5)

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   import random def max(lst): max = 0 for e in lst: if e > max: max = e return max lst = [] for i in range(100): lst.append(random.randint(0, 1000)) print(max(lst))

   (q5_answer)

3. Write a function sum_of_squares(xs) that computes the sum of the squares of the numbers in the list xs. For example, sum_of_squares([2, 3, 4]) should return 4+9+16 which is 29:

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   (ex_7_11)

4. • Question
   • Answer

   Write a function to count how many odd numbers are in a list.

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   (ex_9_6)

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   import random def countOdd(lst): odd = 0 for e in lst: if e % 2 != 0: odd = odd + 1 return odd # make a random list to test the function lst = [] for i in range(100): lst.append(random.randint(0, 1000)) print(countOdd(lst))

   (q7_answer)

5. Sum up all the even numbers in a list.

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   (ex_9_7)

6. • Question
   • Answer

   Sum up all the negative numbers in a list.

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   (ex_9_8)

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   import random def sumNegative(lst): sum = 0 for e in lst: if e < 0: sum = sum + e return sum lst = [] for i in range(100): lst.append(random.randrange(-1000, 1000)) print(sumNegative(lst))

   (q9_answer)

7. Count how many words in a list have length 5.

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   (ex_9_9)

8. • Question
   • Answer

   Sum all the elements in a list up to but not including the first even number.

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   (ex_9_10)

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   import random def sum(lst): sum = 0 index = 0 while lst[index] % 2 != 0 and index < len(lst): sum = sum + lst[index] index = index + 1 return sum lst = [] for i in range(100): lst.append(random.randint(0,1000)) print(sum(lst))

   (q11_answer)

9. Count how many words occur in a list up to and including the first occurrence of the word “sam”.

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   (ex_9_11)

10. • Question
    • Answer

    Although Python provides us with many list methods, it is good practice and very instructive to think about how they are implemented. Implement a Python function that works like the following:

    1. count
    2. in
    3. reverse
    4. index
    5. insert

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    (ex_9_12)

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    def count(obj, lst): count = 0 for e in lst: if e == obj: count = count + 1 return count def is_in(obj, lst): # cannot be called in() because in is a reserved keyword for e in lst: if e == obj: return True return False def reverse(lst): reversed = [] for i in range(len(lst)-1, -1, -1): # step through the original list backwards reversed.append(lst[i]) return reversed def index(obj, lst): for i in range(len(lst)): if lst[i] == obj: return i return -1 def insert(obj, index, lst): newlst = [] for i in range(len(lst)): if i == index: newlst.append(obj) newlst.append(lst[i]) return newlst lst = [0, 1, 1, 2, 2, 3, 4, 5, 6, 7, 8, 9] print(count(1, lst)) print(is_in(4, lst)) print(reverse(lst)) print(index(2, lst)) print(insert('cat', 4, lst))

    (q13_answer)

11. Write a function replace(s, old, new) that replaces all occurences of old with new in a string s:

    test(replace('Mississippi', 'i', 'I'), 'MIssIssIppI')
    
    s = 'I love spom!  Spom is my favorite food.  Spom, spom, spom, yum!'
    test(replace(s, 'om', 'am'),
           'I love spam!  Spam is my favorite food.  Spam, spam, spam, yum!')
    
    test(replace(s, 'o', 'a'),
           'I lave spam!  Spam is my favarite faad.  Spam, spam, spam, yum!')
    

    Hint: use the split and join methods.

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    (ex_9_13)