VE477 Lab 1

1 C programming

Using the C standard library, write an efficient implementation of the following data structures:

• Dictionary with the seven basic operation. Use sorted double link lists.

• Implement hash tables.

2 Starting with Python

Python is an interpreted programming language first developed in the early 1990s. Being high-level and general purpose it is widely used in computer science and various fields of engineering.

Install Python 3 and run the python3 command in a terminal. On Linux systems it is recommended to install software through the package manager.

Basic prompt

At the python prompt run the following basic commands:

• print("Good morning!")

• (1+2+3*2)/3\%5

• a=0; b=a+3; b=3*b; print(b)

4 # print("Good morning!")

5 print(I said "Good morning!")

• print("Good\

• Morning!")

8 a="good"; b="morning"; print(a + " " + b + "!")

9 nb = input("Input a number: ")

10 help()

Arrays

Python has no native implementation for arrays but instead features tuples, lists, and dictionaries. List: simple list of values; index starts at 0;

Tuples: similar to lists but read-only;

Dictionaries: values are not numbered, neither are they ordered; values can be accessed using keys;

Example

1 # tuple

2 days = ('Monday','Tuesday','Wednesday','Thursday','Friday','Saturday', 'Sunday')

3 # list

• students = ['Sam', 'Tom', 'Laura', 'Dave', 'Sarah']

• print(students[2])

• students.append('Catherine')

7 del students[3]

• print(students[2:4])

9 # dictionary

10 gradebook = {'Andrew Parson': [ 'a-', 'b', 'c+'], \

11 'Paul Black': [ 'a-', 'b+', 'a+' ]}

12 del gradebook['Andrew Parson']

13 gradebook['Angela Tree'] = ['d', 'c-', 'f']

14 gradebook

Loops and conditional statements

In the rest of the lab it is recommended to write the code is a text editor and then run it from the terminal using the command python filename.py.

In Python any code must be indented. A program that is not properly indented will not run.

If statement

• #!/usr/bin/python

• a=0; b=1; c=4

3 if a < 3:

• print(a)

5 if a < 3 and b > 0:

• print (c)

7 elif b == -1:

• print(b)

• else:

10 print(a)

Ternary operator

1 a=0; b=1

2 a if a < b else b

While loops

• #!/usr/bin/python

• a=0

3 while a != 0:

• a = input("Input a number: ")

• a+=1

• print(a)

• print('Bye')

For loops

• #!/usr/bin/python

• for i in list(range(3,12,2)):

• print(i)

• students = ['Sam', 'Tom', 'Laura', 'Dave', 'Sarah']

5 for i in students:

• print("{} is a student".format(i))

Defining and calling functions

Defining functions requires to use the keyword def. Python programs do not need to define a main function.

Simple functions

1 def gm(course):

• return "Good morning " + course + "!"

• course='ve477'

• message=gm(course)

• print(message)

• print(gm(input("Input course code: ")))

7 def list(students,courses):

• for i in students:

• print(i)

10 del students[1]

11 courses.append('ve281')

12 return students,courses

13 c = ['ve477', 've370']

14 s = ['Sam', 'Tom', 'Laura', 'Dave', 'Sarah']

15 a,b=list(s, c)

16 print(students)

17 print(a, b, d, e)

Function arguments

1 def list(students,courses):

• for i in students:

• print(i)

• del students[1]

• courses.append('ve281')

6 return students,courses

7 c = ['ve477', 've370']

8 s = ['Sam', 'Tom', 'Laura', 'Dave', 'Sarah']

9 # the input order can be changed

10 d,e=list(courses=c,students=s)

11 # define a function with a variable number of input

12 def varin(*args):

13 return args

14 varin(1,2,3); varin(1); varin(1,2,3,4,5,6,7,8)

15 # define a function with a variable number of keywords

16 def varkw(**kwargs):

17 return kwargs

18 varkw(students=['Sam', 'Tom'], courses=['ve477', 've370'],\

19 sports=['tennis', 'soccer'])

First class functions

In Python a function can be passed as an argument or returned by a function.

1 def adding(x):

• def add(y):

• return x+y

• return add

• add_2=adding(2)

• print(add_2(123))

List, set, and dictionary comprehensions

A list, set, or dictionary comprehension is a way to construct new lists, sets, or dictionaries from existing ones. It follows a syntax similar to set definition in mathematics.

1 [i+3 for i in [1, 2, 3]]

2 [5*i for i in [3, 4, 5, 6, 7] if i < 5]

3 {x for x in 'abcdef' if x not in 'abc'}

4 {i: i**3 for i in range(2,10,3)}

Lambda functions

A Lambda function is a Python facility allowing to embed a function within the code. It can be viewed as an “embedded function” which does not need to be declared using def.

Basic use

1 l = [lambda x: x ** 2, lambda x: x ** 3, lambda x: x ** 4]

2 for i in l:

• print(i(2))

4 min = (lambda x, y: x if x < y else y)

• min(12,16)

Lambda and map functions

1 # distances in Miles

2 mi=[ 123, 2, 45, 87.2, 192 ]

3 # distances in km

4 km=map(lambda x: x*1.609344,mi)

5 for i in km:

• print(i)

Lambda and filter functions

1 gradebook = {'Andrew Parson': [ 55, 40, 60], 'Paul Black': [ 85, 80, 95 ]}

• list(filter(lambda x: x < 60, gradebook['Andrew Parson']))

Exercise

Python 3 short practice:

• Construct more complex examples showing how to use:

– Lambda functions with map(), and filter()

– List, set, and dictionary comprehensions

• Write a phone book application, where the user can add, remove, and edit entries.