COEN140-Lab1: Python Practice Solved

Part I
Exercise 1: Numbers
Run the following in python shell.

>>> a=123+222 # integer addition

>>> print(a)

>>> b = 1.5*4    # floating-point multiplication

>>> print(b)

>>> c=2**10      # 2 to the power 10

>>> print(c)

>>> import math

>>> print(math.pi)

>>> print(math.sqrt(36))

>>> import random

>>> a=random.random()

>>> print(‘a=’, a)

>>> b = random.choice([1,2,3,4])

>>> print(‘b=’, b)

 

Exercise 2: Strings
Run the following in python shell.

>>> S=’Spam’   # make a 4-character string, and assign it to a name

>>> len(S)         # Length

>>> S[0]  # the 1st item in S, indexing by zero-based position

>>> S[1]  # the 2nd item from the left

>>> S[-1]        # the last item from the end in S

>>> S[-2] # the second-to-last item from the end

>>> S[len(S)-1]

>>> S[1:3] # Slice of S from offsets 1 through 2 (not 3)

>>> S = ‘z’ + S[1:]

>>> S

 

Exercise 3: Lists
Run the following in python shell.

>>> L=[123, ‘spam’, 1.23]  # A list of three different-type objects

>>> len(L) # number of items in the list

>>> L[0]

>>> L[:-1]   # Slicing a list returns a new list

>>> L+[4,5,6]  # contact/repeat make new lists too

>>> L*2 # repeat

>>> L  # we are not changing the original list

>>> M = [‘bb’, ‘aa’, ‘cc’]

>>> M.sort()

>>> M

>>> M.reverse()

>>> M

>>> M = [[1,2,3], [4,5,6], [7,8,9]]   # a list that contains three other lists, 3x3 matrix

>>> M[1]   # get row 2

>>> M[1][2]  # get row 2, then get item 3 within the row

>>> diag = [M[i][i] for i in [0, 1, 2]]  >>> diag


>>> doubles = [c * 2 for c in 'spam']  

>>> doubles


>>> list(range(4))     # 0..3 (list() required in 3.X)


>>> list(range(−6, 7, 2))    # −6 to +6 by 2 (need list() in 3.X)  

>>> [[x ** 2, x **
3] for x in range(4)]     # Multiple values, “if” filters >>> [[x, x/2, x * 2] for x in range(−6, 7, 2) if x > 0]  

 

Exercise 4: Linear Algebra
4.1. Write a NumPy program to compute the multiplication of the following two matrixes, using numpy.dot and numpy.matmul, and print the results.

p = [[1, 0], [0, 1], [1,1]] q = [[1, 2], [3, 4]]

4.2 Write a NumPy program to find the L2-norm of vector v=numpy.arange(7) and matrix numpy.matrix('1, 2; 3, 4'). Print the results.

Note: the L2-norm of a vector 𝐯 = [v1, v2, . . . , vN]  is defined as:

 

‖𝐯‖2 ≜ √v12 + v22+. . . +vN2 

 4.3 Write a NumPy program to compute the inverse of matrix m = np.array([[1,2],[3,4]]).

 

Exercise 5: Tuples
Run the following in python shell.

>>> T = (1, 2, 3, 4)   # A 4-item tuple  

>>> len(T)
 # Length

>> T + (5, 6)
 # Concatenation  

>>> T[0] # Indexing, slicing, and more  

>>> T.index(4) # Tuple methods: 4 appears at offset 3  

>>> T.count(4) # 4 appears once
 

>>> T[0] = 2 # Tuples are immutable  

...error text omitted...
 

TypeError: 'tuple' object does not support item assignment  

>>> T = (2,) + T[1:] # Make a new tuple for a new value 

 >>> T


 >>>  T = 'spam', 3.0, [11, 22, 33] 


 >>>  T[1]  

 >>>  T[2][1] 


Exercise 6: if Tests and Syntax Rules
Create a file test_if.py that contains the following lines, then run the module, show the results in the lab report. x =1  

if x:  

     y= 2       if y:  

          print('block2')       print('block1')  print('block0')  

 

choice = 'ham'

if choice == 'spam':  # the equivalent if statement     print(1.25)  elif choice == 'ham':

    print(1.99) elif choice == 'eggs':

    print(0.99) elif choice == 'bacon':

    print(1.10) else:

    print('Bad choice')

 

Exercise 7: while and for Loops
Run the following in python shell.

>>> x = 'spam'

>>> while x:                 # while x is not empty   print(x,end=' ')  # in 2.X use print x    x=x[1:]              # strip first character off x

 

>>> a=0; b=10 

>>> while a<b:          # one way to code counter loops   print(a,end=’ ‘) 

             a+=1               # or, a = a + 1 

 

>>> x=10 

>>> while x: 

            x=x-1                              # or, x -=1 

            if x%2 !=0: continue     # odd? – skip print           print(x, end=' ') 

 

>>> for x in ["spam", "eggs", "ham"]: 

               print(x, end=' ') 

 

>>> sum = 0 

>>> for x in [1, 2, 3, 4]: 

            sum = sum + x           

>>> sum 

 

>>> prod = 1 

>>> for item in [1,2,3,4]: prod*= item 

>>> prod 

Part II
Exercise 8: Functions
 

Create fun1.py and fun2.py as the following, run them, show the results, and explain what each function does (and the results) in your own words.

 

 

 

fun1.py
 

def times(x,y):        # create and assign function       return x*y        # Body executed when called

 

a = times(2,4) b = times(‘Ok’, 4)          # Functions are “typeless”

 

print(a,’\n’, b)



 

s1 = "SPAM"

s2 = "SCAM"

result1 = intersect(s1, s2) print(result1)

 

result2 = intersect([1, 2, 3], (1, 4))       # mixed type: list & tuple print(result2)

 

Exercise 9: modules
 

Create module.py, test1_module.py, test2_module.py, and test3_module.py as the following, run test1_module.py, test2_module, and test3_module.py, show the results, and explain your findings.

 

module.py
 

a = 10 b = 20

 

def adder(x, y):      # module attribute

      z = x + y

      return z

 

def multiplier(x, y):

      z = x*y

      return z

 

 

test1_module.py
 

import module                                # Get module as a whole  result = module.adder(module.a, module.b)      # Qualify to get names print(result)

 

test2_module.py
 

c = 5 d = 10

from module import adder          # Copy out an attribute  result = adder(c, d)                       # No need to qualify name print(result)

 

from module import a, b, multiplier   # Copy out multiple attributes result = multiplier(a, b) print(result)

test3_module.py
 

from module import *     # Copy out all attributes result1 = adder(a, b) result2 = multiplier(a, b)

print(result1, '\n', result2)

 

 

Exercise 10: built-in attribute of modules
 

Each module has a built-in attribute: __name__.  

If the file is being run as a top-level program file, __name__ is set to the string “__main__” when it starts.

If the file is being imported, __name__ is instead set to the module’s name as known by its clients.

Read the following example:  

 

runme.py
 

def tester()       print “It’s Christmas in Heaven…”

 

if __name__==’__main__’:       # Only when run

   tester()                                     # Not when imported

 

 

(1)               Create minmax.py as the following, run it, show the results, and explain what this .py file does. 

 

def minmax(test,array):       res = array[0]       for arg in array[1:]:             if test(arg, res):

                res = arg

      return res

 

def lessthan(x,y): return x<y

def grtrthan(x,y): return x>y

 

print(minmax(lessthan, [4,2,1,5,6,3]))    # self-test code print(minmax(grtrthan, [4,2,1,5,6,3]))

 

 

(2)               Create minimax2.py as the following, run it, show the results, and explain what this .py file does. 

 

def minmax(test,array):       res = array[0]       for arg in array[1:]:             if test(arg, res):

                res = arg

      return res

 

def lessthan(x,y): return x<y

def grtrthan(x,y): return x>y

 

if __name__ == '__main__':

      print(minmax(lessthan, [4,2,1,5,6,3]))    # self-test code       print(minmax(grtrthan, [4,2,1,5,6,3]))

 

(3)       From python shell, execute the following two commands, show the results, and explain your findings. 

 

import minmax

import minmax2


 

Exercise 11: Object-Oriented Programming and Classes
 

(1)       Create class1.py as the following, run it, show the results, and explain what the code does. 

 

class FirstClass:  # define a class object     def setdata(self,value1, value2): # Define class’s methods         self.data1=value1                   # self is the instance         self.data2=value2     def display(self):       

        print(self.data1, '\n', self.data2, '\n')

 

     

x=FirstClass() # make one instance

 

x.setdata("King Arthur",-5)   # Call methods: self is x

x.display()  

 

 

x.data1="QQ"

x.data2=-3

x.display()

 

x.anothername="spam"

x.display() print(x.anothername)

 

(2)       Class Inheritance: create class2.py as the following, run it, show the results, and explain what the code does. 

 

 

class FirstClass:     def setdata(self,value1, value2):  

        self.data1=value1         self.data2=value2     def display(self):        

        print(self.data1, '\n', self.data2, '\n')

 

class SecondClass(FirstClass): # inherits setdata and display

    def adder(self,val1,val2):     # create adder

                a=val1+val2                 print(a)

 

z=SecondClass() # make one instance  z.setdata(10,20)

z.display()

z.adder(-5,-10)

 

(3)       The constructor method: create class3.py as the following, run it, show the results, and explain what the code does. 

 
 

class Person:

    def __init__(self, name, jobs, age=None): # __init__ is the constructor method of a class

                                            #it is to initialize the object's states         self.name=name         self.jobs=jobs

        self.age=age

 

    def info(self):       # another method of the class         return (self.name, self.jobs)

 

rec1 = Person('Bob', ['dev', 'mgr'], 40.5)

rec2 = Person('Sue', ['dev', 'cto'])

 

print(rec1.jobs)

print(rec2.info())

 

(4)       Classes are attributes in modules: create class_as_module.py as the following, run it, show the results, and explain what the code does. 

 

class_as_module.py 
 

import class3

 

rec3 = class3.Person('Jane', ['dev', 'mgr'], 30)

 

 

print(rec3.age) print(rec3.info()) from class3 import Person

 

rec4 = Person('Mike', ['dev', 'mgr'], 35) print(rec4.age) print(rec4.info())