Exercises 10.31 Exercises
2.
Create a list called
myList with the following six items: 76, 92.3, “hello”, True, 4, 76. Begin with the empty list shown below, and add 6 statements to add each item, one per item. The first three statements should use the append method to append the item to the list, and the last three statements should use concatenation.
Solution.
myList = []
myList.append(76)
myList.append(92.3)
myList.append("hello")
myList = myList + [True]
myList = myList + [4]
myList = myList + [76]
print(myList)
3.
Starting with the list of the previous exercise, write Python statements to do the following:
-
Append “apple” and 76 to the list.
-
Insert the value “cat” at position 3.
-
Insert the value 99 at the start of the list.
-
Find the index of “hello”.
-
Count the number of 76s in the list.
-
Remove the first occurrence of 76 from the list.
Solution.
myList = [76, 92.3, 'hello', True, 4, 76]
myList.append("apple") # a
myList.append(76) # a
myList.insert(3, "cat") # b
myList.insert(0, 99) # c
print(myList.index("hello")) # d
print(myList.count(76)) # e
myList.remove(76) # f
myList.pop(myList.index(True)) # g
print (myList)
4.
Write a function called
average that takes a list of numbers as a parameter and returns the average of the numbers.
Solution.
def average(numlist):
total = 0
for num in numlist:
total = total + num
return total / len(numlist)
5.
Write a Python function named
max that takes a parameter containing a nonempty list of integers and returns the maximum value. (Note: there is a builtin function named max but pretend you cannot use it.)
Solution.
def max(lst):
max = lst[0]
for e in lst:
if e > max:
max = e
return max
6.
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:
7.
Write a function to count how many odd numbers are in a list.
Solution.
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))
8.
Sum up all the even numbers in a list.
9.
Sum up all the negative numbers in a list.
Solution.
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))
10.
Count how many words in a list have length 5.
11.
Solution.
import random
def sum(lst):
sum = 0
index = 0
while index < len(lst) and lst[index] % 2 != 0:
sum = sum + lst[index]
index = index + 1
return sum
lst = []
for i in range(100):
lst.append(random.randint(0,1000))
print(sum(lst))
12.
Count how many words occur in a list up to and including the first occurrence of the word “sam”.
13.
Solution.
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))
14.
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!')
15.
Here are the rules for an L-system that creates something that resembles a common garden herb. Implement the following rules and try it. Use an angle of 25.7 degrees.
H H --> HFX[+H][-H] X --> X[-FFF][+FFF]FX
Solution.
import turtle
def createLSystem(numIters, axiom):
startString = axiom
endString = ""
for i in range(numIters):
endString = processString(startString)
startString = endString
return endString
def processString(oldStr):
newstr = ""
for ch in oldStr:
newstr = newstr + applyRules(ch)
return newstr
def applyRules(ch):
newstr = ""
if ch == 'H':
newstr = 'HFX[+H][-H]' # Rule 1
elif ch == 'X':
newstr = 'X[-FFF][+FFF]FX'
else:
newstr = ch # no rules apply so keep the character
return newstr
def drawLsystem(aTurtle, instructions, angle, distance):
savedInfoList = []
for cmd in instructions:
if cmd == 'F':
aTurtle.forward(distance)
elif cmd == 'B':
aTurtle.backward(distance)
elif cmd == '+':
aTurtle.right(angle)
elif cmd == '-':
aTurtle.left(angle)
elif cmd == '[':
savedInfoList.append([aTurtle.heading(), aTurtle.xcor(), aTurtle.ycor()])
#print(savedInfoList)
elif cmd == ']':
newInfo = savedInfoList.pop()
aTurtle.setheading(newInfo[0])
aTurtle.setposition(newInfo[1], newInfo[2])
def main():
inst = createLSystem(4, "H") # create the string
print(inst)
t = turtle.Turtle() # create the turtle
wn = turtle.Screen()
t.up()
t.back(200)
t.down()
t.speed(9)
drawLsystem(t, inst, 27.5, 5) # draw the picture
wn.exitonclick()
main()
16.
Here is another L-System. Use an Angle of 25.
F F --> F[-F]F[+F]F
17.
Create a list named
randlist containing 100 random integers between 0 and 1000 (use iteration, append, and the random module).
Solution.
import random
randlist = []
for i in range(100):
randlist.append(random.randint(0, 1000))
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