Advanced Python — diagnostic exercise

1. Use the time module's .ctime() function to display the current time in human-readable form.

   Example output

   Fri Dec 27 13:10:51 2019
   

   Preferably, put the code you need into a stand-alone file.

   Solution

   import time
   print(time.time())
   print(time.ctime())
   

2. Write script (or statements in an interactive session) to input two numbers from the user, then calculate and display their ratio (divide the first by the second). Use a try - except block on the division, to trap any errors.

   Example output

   $ ./q-try-ratio.py
   first number? 12
   second number? 13
   12.000000 / 13.000000 equals 0.923077
   $ ./q-try-ratio.py
   first number? 12
   second number? 0
   Error:  float division by zero
   $ ./q-try-ratio.py
   first number? 0
   second number? 0
   Got exception -->float division by zero<--
   $ 
   

   Solution

   #!/usr/bin/env python3
   
   x = float(input('first number? '))
   y = float(input('second number? '))
   
   try:
       z = x / y
       print('{:f} / {:f} = {:f}'.format(x, y, z))
   except Exception as e:
       print('Got exception -->{}<--'.format(e))
   #--------
   

3. Write a function named average3() that accepts three numbers, and returns their average.

   Then write a simple program that includes the function, uses it to calculate an average, and displays the result. The program can get three numbers from the user, or just "hardcode" three numbers, whichever you prefer. The point is to demonstrate the use of the function.

   Example usage and output

   answer = average3(17, -3.5, 8)
   print(answer)
   7.166666666666667
   

   Solution

   #!/usr/bin/env python3
   
   def average3(x, y, z):
       return (x + y + z) / 3
   #--------
   
   a = float(input('first number? '))
   b = float(input('second number? '))
   c = float(input('third number? '))
   
   avg = average3(a, b, c)
   print('Average of {}, {}, {} equals {}'.format(a,b,c, avg))
   

4. Write a script (or an interactive session) that uses a loop to accept text strings from the keyboard and collect them into a list of strings. Stop when the user enters an empty text string; then print out the list.

   Example usage

   Next string?  hello, world
   Next string?  goodbye, earth
   Next string?  stop, I want to get off.
   Next string?  ... and blah blah blah...
   Next string?  
   
   ['hello, world', 'goodbye, earth', 'stop, I want to get off.', '... and blah blah blah...']
   

   Solution

5. Write a function that accepts a list of text strings (such as the one from the previous question), and returns a dictionary of the characters in all the strings and how ofter they occur.

   Then write a simple program that includes the function and uses it. Display the resulting dictionary.

   Example usage and output

   cd = make_char_dict(result)
   print(cd)
   {'h': 5, 'e': 4, 'l': 6, 'o': 7, ',': 3, ' ': 11, 'w': 2, 'r': 2, 'd': 3, 'g': 2, 'b': 4, 'y': 1, 'a': 6, 't': 5, 's': 1, 'p': 1, 'I': 1, 'n': 2, 'f': 2, '.': 7}
   
   for c, v in cd.items():
       print(c, v)
   h 5
   e 4
   l 6
   o 7
   , 3
     11
   w 2
   r 2
   d 3
   g 2
   b 4
   y 1
   a 6
   t 5
   s 1
   p 1
   I 1
   n 2
   f 2
   . 7
   

   Solution

   #!/usr/bin/env python3
   
   def question1(strings):
      chars = {}
       for s in strings:
           for c in s:
               if c not in chars:
                   chars[c] = 0
               chars[c] += 1
   
       return chars
   #--------
   

6. Write a program (or script) that accepts command-line arguments, then displays each of them in reverse order.

   Example run, in a shell

   $ python echo-cmdline.py a bc def ghij klmno pqrst uvwxyz
   uvwxyz
   pqrst
   klmno
   ghij
   def
   bc
   a
   echo-cmdline.py
   

   Solution

   #!/usr/bin/env python3
   #       Multiple solutions for command-line arguments question
   import sys
   
   
   # (1) use a loop - naive approach
   mylist = []
   for a in sys.argv:
       mylist.append(a)
   for i in range(len(mylist)-1, -1, -1):
       print(mylist[i])
   print('#----')
   
   
   # (2) list comprehension copy, reverse-index printing
   mylist = [ a for a in sys.argv ]
   for a in mylist[::-1] :
       print(a)
   print('#----')
   
   
   # (3) slicing operation copy, reverse-index printing
   mylist = sys.argv[:]
   for a in sys.argv[::-1] :
       print(a)
   print('#----')
   
   
   # (4) not a copy, just an "alias" name - not even needed
   mylist = sys.argv
   for a in sys.argv[::-1] :
       print(a)
   print('#----')