To Lecture Notes

IT 211 -- Feb 13, 2019

Lists

1. A Python list is a collection of items separated with commas and delimited with square brakets, for example:
   

   list1 = [34, 59, 61, 23, 43]
   

2. We can print all of the items in the list using a for statement:
   

   for n in list1:
       print(n)
       
   # Output:
   34
   59
   61
   23
   43
   

   or
   

   for n in list1:
       print(n, end=" -- ")
       
   # Output:
   34 -- 59 -- 61 -- 23 -- 43 --
   

   You can also print a list directly like this:
   

   print(list1)
   
   # Output:
   [34, 59, 61, 23, 43]
   

3. We can extract individual items from the list using the index operator [ ]:
   

   print(list1[3])
   
   # Output:
   23
   

   This result is explained by this table:
   
   

   list1	Index	0	1	2	3	4
   	Value	34	59	61	23	43

   
   Remember that computer scientists start counting at 0 instead of 1, thus the indices for a list start at 0.
4. This suggests a different way to print the values in the array:
   

   for n in range(0, len(list1):
       print(n, end="; ")
       
   # Output:
   34; 59; 61; 23; 43;
   

5. The items in a list often are, but are not necessarily all of the same datatype, for example:
   

   list2 = [154, "dog", 3.14159, True]
   for value in list2:
       print(value)
   # Output:
   154
   dog
   3.14159
   True
   

6. We can check the datatypes of the values in the list like this:
   

   for value in list2:
       print(type(value))
   
   # Output:
   <class 'int'>
   <class 'str'>
   <class 'float'>
   <class 'bool'>
   

Project 6

• Look at the Project 6 Description.
• Collect (from the web or from pictures you took yourself) 8 to 20 images, which your script will organize into 3 or more photo albums.

More about User Defined Methods

• Method names follow the same spelling rules as local variables: the name must start with a lowercase letter or underscore, and it must consist of lower case letters, underscores, or digits.
• These are all properly spelled method names using underscore notation:
  

  f  f_5  find_record  update_vehicle_miles
  

• You can also use lower camel casing to spell method or instance variable names:
  

  f  f5  findRecord  updateVehicleMiles
  

• Look at these examples:
  
  StateRiddles   ToFahr   OldMacDonald   MySqrt
• Methods are used for three reasons:
  
  1. Modularization: the various parts of computer software can be developed and tested separately (see the StateRiddles Example).
  2. Code Reuse: instead of repeating code in various parts of the software, put the code in a method and then call the method more than once (see the OldMacDonald Example).
  3. Encapsulation: the user of a method does not need to understand the code in the method, only how to invoke the method (see the MySqrt Example).

Practice Problems

Write user and test defined methods. The method header is shown first with the description on subsequent lines.

1. def print_greeting( ):
        Print a generic greeting, such as "Hello, how are you?"

   # Ans:
   def print_greeting( ):
       print("Hello, how are you?")
       
   print_greeting( )
   
   # Output:
   Hello, how are you?
   

2. def print_greeting(the_person):
       Print a greeting to the person whose name is passed in as a parameter.
   

   def print_greeting(the_person):
      print(f"Hello, {the_person}, how are you?")
      
   print_greeting("Alice")
   
   # Output:
   Hello, Alice, how are you?
   

3. def print_greeting(the_person):
       Return a greeting to the person whose name is passed in as a parameter
   

    
   # Ans:
   def get_greeting(the_name):
       return "Hello, " + the_name + ", how are you?"
       
   print(get_greeting("Alice"))
   
   # Ans:
   Hello, Alice, how are you?
   

4. def meters(feet, inches):
       Return the length given in feet and inches converted to meters.
       Use the fact that one inch == 2.54 centimeters.
   

   # Ans: 
   def to_meter(feet, inches):
       m = (feet * 12.0 + inches) * 2.54 / 100.0
       return m
       
   print(to_meter(2, 3)
   
   # Output: 0.6912
   

5. def to_feet_inches(meters):
        Return as a string the length given in meters converted to meters
        Use the fact that one inch == 2.54 centimeters.
   

   def to_feet_inches(meters):
   f = meters * 100.0 / (2.54 * 12.0)
   feet = int(f)
   inches = int(round((f - feet) * 12.0, 0))
   output = str(feet) + "' " + str(inches) + '"'
   return output
   
   print(to_feet_inches(0.6912))

   # Output:
   2' 3"
   

Project 5

• Look at the Project 5 Description.