IT 117: Intermediate Scripting - Answers to Questions on Final Exam

IT 117: Intermediate Scripting
Answers to Questions on Final Exam - Even Columns

Each of the following questions are worth 3 points.

Write a Python expression to see if the set s1 contains 5.
```
5 in s1
```
To create a new kind of object, what must you define?
```
a class
```
What are the entries in a dictionary?
```
key - value pairs
```
In Python what must the special method used to create an object be named?
```
__init__
```
What string value does Python think of as False in an if statement?
```
the empty string
```
Write the Python expression that gives the value of the first command line argument.
```
sys.argv[1]
```

What does the . (dot) in a regular expression match?

one occurrence of any character, except the newline

What is the name of the method that will return a string representation of an object?
```
__str__
```
What is the name of the module that allows you to interact with the Python interpreter?
```
sys
```
Write the regular expression that is equivalent to * on the Unix command line.
```
.*
```
What do you call the special method that is used to create an object?
```
constructor
```
Write the Python expression you would use to get a list of all entries in your current directory.
```
os.listdir('.')
```

Can the key in a dictionary entry be any data type?

no. you can only use values that are immutable, that cannot be changed

What do you call an object that is created from a class?
```
an instance
```

What does the + in a regular expression match?

1 or more occurrences of the character that comes before it

What are three things are found in a regular expression?
```
ordinary characters, meta-characters, character classes
```
What do you call the special class of methods that do things like provide a string representation of an object and convert one data type into another?
```
magic methods
```
What do you call a function that calls itself?
```
a recursive function
```

What two things must be true about a recursive algorithm for it to work?

there must be a condition under which recusion will stop
 the recursive call must approach this condition

What is the name of the module that allows you to interact with the operating system?
```
os
```

The following questions require you to write code.
Each question is worth 10 points.

Define the RECURSIVE function count_down which takes a single parameter, num, an integer.
The function should print the numbers, starting with num, down to 0, one number to a line.
For example, when you call count_down(5), the output should be
```
5
4
3
2
1
0
```
```
def count_down(num):
    print(num)
    if num > 0:
        count_down(num - 1)
```

Define the class Employee with the following attributes

first_name
last_name
id

All attributes must be hidden and must have accessor methods.
There must also be a method which will return a string representation of the object which should contain the value of all fields.

class Employee:
def __init__(self, first_name, last_name, id):
    self.__first_name = first_name
    self.__last_name  = last_name
    self.__id         = id
    
def get_first_name(self):
    return self.__first_name

def get_last_name(self):
    return self.__last_name

def get_id(self):
    return self.__id 

def __str__(self):
    return self.__first_name + " " + self.__last_name + ", ID: " + self.get_id()

Define the function python_count that takes a single parameter, dir_path, a path to a directory.
The script should create a list of the entries in dir_path.
Then it should loop through this list and count the number of entries with a ".py" extension.
This should be done using the string method endswith.
The function should return this count.
```
def python_count(dir_path):
	file_list = os.listdir(dir_path)
	count = 0
	for file in file_list:
	    if file.endswith('.py'):
	        count += 1
	return count
```
Write the regular expression you would use to both match and extract the value of an IP address from lines like the following
```
205.236.184.22 
2.2.3.4
13.26.34.202
...
```
```
(\d{1,3}\.\d{1,3}\.\d{1,3})
```