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6
Python Programming
Unit I Introduction : Fundamental ideas of Computer Science - Strings, Assignment, and Comments
- Numeric Data types and Character sets – Expressions – Loops and Selection Statements: Definite iteration: the for Loop - selection: if and if-else statements - Conditional iteration: the while Loop Unit II Strings and Text Files: Accessing Characters and substrings in strings - Data encryption- Strings and Number systems- String methods – Text - Lists and Dictionaries: Lists – Dictionaries – Design with Functions: A Quick review - Problem Solving with top-Down Design - Design with recursive Functions - Managing a Program‘s namespace - Higher-Order Functions Unit III Design with Classes: Getting inside Objects and Classes – Data-Modeling Examples – Building a New Data Structure – The Two – Dimensional Grid - Structuring Classes with Inheritance and Polymorphism - GraphicalUserInterfaces. The Behavior of terminal-Based programs and GUI-Based programs - Coding Simple GUI-Based programs - Windows and Window Components - Command Buttons and responding to events Unit IV Working with Python Packages: NumPy Library-Ndarray – Basic Operations – Indexing, Slicing and Iteration – Array manipulation - Pandas – The Series – The DataFrame - The Index Objects – Data Vizualization with Matplotlib – The Matplotlib Architecture – pyplot – The Plotting Window – Adding Elements to the Chart – Line Charts – Bar Charts – Pie charts Unit V Django: Installing Django – Building an Application – Project Creation – Designing the DataSchema - Creating an administration site for models - Working with QuerySets and Managers- Retrieving Objects – Building List and Detail Views
Basics of Python Programming
UNIT – I
Python has a simple syntax similar to the English language. Python has syntax that allows developers to write programs with fewer lines than some other programming languages. Python runs on an interpreter system, meaning that code can be executed as soon as it is written. This means that prototyping can be very quick. What is Python? Python is a popular programming language. It was created by Guido van Rossum, and released in 1991. It is used for:
- web development (server-side),
- software development,
- mathematics,
- System scripting. What can Python do? Python can be used on a server to create web applications.
- Python can be used alongside software to create workflows.
- Python can connect to database systems. It can also read and modify files.
- Python can be used to handle big data and perform complex mathematics.
- Python can be used for rapid prototyping, or for production-ready software development. Why Python?
- Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).
- Python has a simple syntax similar to the English language.
- Python has syntax that allows developers to write programs with fewer lines than some other programming languages.
- Python runs on an interpreter system, meaning that code can be executed as soon as it is written, This means that prototyping can be very quick.
- Python can be treated in a procedural way, an object-oriented way or a functional way. Python Syntax compared to other programming languages
- Python was designed for readability, and has some similarities to the English language with influence from mathematics.
- Python uses new lines to complete a command, as opposed to other programming languages which often use semicolons or parentheses.
- Python relies on indentation, using whitespace, to define scope; such as the scope of loops, functions and classes. Other programming languages often use curly-brackets for this purpose.
my_set = {1, 2, 3} Algorithms Algorithms are step-by-step processes used to solve problems. They can involve searching, sorting, and more complex operations. def binary_search(arr, target): left, right = 0, len(arr) - 1 while left <= right: mid = left + (right - left) // 2 if arr[mid] == target: return mid elif arr[mid] < target: left = mid + 1 else: right = mid - 1 return - 1 Recursion Recursion is a technique where a function calls itself to solve a smaller instance of a problem. def factorial(n): if n == 0: return 1 else: return n * factorial(n - 1) Object-Oriented Programming (OOP) OOP is a programming paradigm that uses objects to structure code. Classes define objects with attributes (variables) and methods (functions). class Circle: def init (self, radius): self.radius = radius def area(self): return 3.14 * self.radius ** 2 File Handling Reading from and writing to files. with open("myfile.txt", "r") as f: content = f.read() with open("output.txt", "w") as f: f.write("Hello, world!")
Python String
A string is a data structure in Python that represents a sequence of characters. It is an immutable data type, meaning that once you have created a string, you cannot change it. Strings are used widely in many different applications, such as storing and manipulating text data, representing names, addresses, and other types of data that can be represented as text. Creating a String in Python Strings in Python can be created using single quotes or double quotes or even triple quotes. Example
Python Program for
Creating a String
with single Quotes Output
String1 = 'Welcome to the AVSCAS' String with the use of Single Quotes: print("String with the use of Single Quotes: ") Welcome to the AVSCAS print(String1) String with the use of Double Quotes:
Creating a String I'm ashwin
with double Quotes
String1 = "I'm ashwin" Creating a multiline String: print("\nString with the use of Double Quotes: ") ''WELCOME TO MCA''' print(String1)
Creating String with triple
Quotes allows multiple lines
String1 = ''WELCOME TO MCA''' print("\nCreating a multiline String: ") print(String1) Accessing characters in Python String
print(String1)
Printing 3rd to 12th character
print("\nSlicing characters from 3-12: ") print(String1[3:12]) Deleting/Updating from a String In Python, the Updation or deletion of characters from a String is not allowed. This will cause an error because item assignment or item deletion from a String is not supported. Although deletion of the entire String is possible with the use of a built-in del keyword. Example Output
Python Program to Delete
characters from a String Initial String: Chandru
String1 = "Chandu" Deleting character at 2nd Index: a print("Initial String: ") print(String1)
Deleting a character
of the String
String2 = String1[0:2] + String1[3:] print("\nDeleting character at 2nd Index: ") print(String2) Formatting of Strings Strings in Python can be formatted with the use of format() method which is a very versatile and powerful tool for formatting Strings. Format method in String contains curly braces {} as placeholders which can hold arguments according to position or keyword to specify the order. Example Output
Python Program for
Formatting of Strings Print String in default order: Welcome
Default order String in Positional order:
String1 = "{} {} {}".format('Welcome) „Master‟ „of‟ „Computer‟ „Application‟ print("Print String in default order: ") String in order of Keywords: print(String1) Master of Computer Applications
Positional Formatting
String1 = "{1} {0} {2}".format („Master‟ „of‟ „Computer‟ „Application‟) print("\nPrint String in Positional order: ") print(String1)
Keyword Formatting
String1 = "{l} {f} {g}".format(M='Master',C='computer',A='Applications') print("\nPrint String in order of Keywords: ") print(String1)
Assignment Statements in Python
Python assignment statements to assign objects to names. The target of an assignment statement is written on the left side of the equal sign (=), and the object on the right can be an arbitrary expression that computes an object. There are some important properties of assignment in Python :-
- Assignment creates object references instead of copying the objects.
- Python creates a variable name the first time when they are assigned a value.
- Names must be assigned before being referenced.
- There are some operations that perform assignments implicitly. Assignment statement forms :- Basic form: This form is the most common form. student = 'Ashwin' Output print(student) Ashwin Tuple assignment
equivalent to: (x, y) = (50, 100) Output
x, y = 50, 100 x = 50 print('x = ', x) y = 100 print('y = ', y) List assignment-> This works in the same way as the tuple assignment. [x, y] = [2, 4] Output print('x = ', x) x = 2 print('y = ', y) y = 4 Sequence assignment Recent version of Python, tuple and list assignment have been generalized into instances of what we now call sequence assignment – any sequence of names can be assigned to any sequence of values, and Python assigns the items one at a time by position. a, b, c = 'AVS' Output print('a = ', a) a = A print('b = ', b) b = V print('c = ', c) C = S Extended Sequence unpacking It allows us to be more flexible in how we select portions of a sequence to assign. p, *q = 'Hello' Output print('p = ', p) p = H print('q = ', q) q = ['e', 'l', 'l', 'o'] Multiple- target assignment x = y = 50 Output print(x, y) 50 50 Augmented assignment The augmented assignment is a shorthand assignment that combines an expression and an assignment. x = 2 Output
equivalent to: x = x + 1 3
x += 1 print(x)
Example Data Types Classes Description Numeric int, float, complex holds numeric values String str holds sequence of characters Sequence list, tuple, range holds collection of items Mapping dict holds data in key-value pair form Boolean bool holds either True or False Set set, frozeenset hold collection of unique items Python String Data Type Python Strings are identified as a contiguous set of characters represented in the quotation marks. Python allows for either pairs of single or double quotes. Subsets of strings can be taken using the slice operator ([ ] and [:] ) with indexes starting at 0 in the beginning of the string and working their way from - 1 at the end. Example Output str = 'Hello World!' Hello World! print (str) H print (str[0]) llo print (str[2:5]) llo World! print (str[2:]) Hello World!Hello World! print (str * 2) Hello World!TEST print (str + "TEST") Python List Data Type Python Lists are the most versatile compound data types. A Python list contains items separated by commas and enclosed within square brackets ([]). To some extent, Python lists are similar to arrays in C. One difference between them is that all the items belonging to a Python list can be of different data type where as C array can store elements related to a particular data type. The values stored in a Python list can be accessed using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the list and working their way to end - 1. The plus (+) sign is the list concatenation operator, and the asterisk (*) is the repetition operator. Example list = [ 'abcd', 786 , 2.23, 'john', 70.2 ] tinylist = [123, 'john'] print (list) # Prints complete list print (list[0]) # Prints first element of the list print (list[1:3]) # Prints elements starting from 2nd till 3rd print (list[2:]) # Prints elements starting from 3rd element print (tinylist * 2) # Prints list two times print (list + tinylist) # Prints concatenated lists
Output ['abcd', 786, 2.23, 'john', 70.2] abcd [786, 2.23] [2.23, 'john', 70.2] [123, 'john', 123, 'john'] ['abcd', 786, 2.23, 'john', 70.2, 123, 'john'] Python Tuple Data Type Python tuple is another sequence data type that is similar to a list. A Python tuple consists of a number of values separated by commas. Unlike lists, however, tuples are enclosed within parentheses. Tuples can be thought of as read-only lists. Example tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 ) tinytuple = (123, 'john') print (tuple) # Prints the complete tuple print (tuple[0]) # Prints first element of the tuple print (tuple[1:3]) # Prints elements of the tuple starting from 2nd till 3rd print (tuple[2:]) # Prints elements of the tuple starting from 3rd element print (tinytuple * 2) # Prints the contents of the tuple twice print (tuple + tinytuple) Output ('abcd', 786, 2.23, 'john', 70.2) abcd (786, 2.23) (2.23, 'john', 70.2) (123, 'john', 123, 'john') ('abcd', 786, 2.23, 'john', 70.2, 123, 'john') Python Boolean Data Types Python boolean type is one of built-in data types which represents one of the two values either True or False. Python bool() function allows you to evaluate the value of any expression and returns either True or False based on the expression. Example Output a = True true print(a) <class 'bool'> print(type(a)) Python Ranges Python range() is an in-built function in Python which returns a sequence of numbers starting from 0 and increments to 1 until it reaches a specified number. Here is the description of the parameters used:
print("Age:", age) John 30 Input Statements
- input ( prompt )
- raw_input ( prompt ) input (): This function first takes the input from the user and converts it into a string. The type of the returned object always will be <class „str‟>. It does not evaluate the expression it justreturns the complete statement as String. For example, Python provides a built-in function called input which takes the input from the user. When the input function is called it stops the program and waits for the user‟s input. Example num = int(input("Enter a number: ")) print(num, " ", type(num)) floatNum = float(input("Enter a decimal number: ")) print(floatNum, " ", type(floatNum)) Output Enter a number: 30 30 <class „int‟> Enter a decimal number: 10. 10.4 <class „float‟> Expressions in Python An expression is a combination of operators and operands that is interpreted to produce some other value. In any programming language, an expression is evaluated as per the precedence of its operators. So that if there is more than one operator in an expression, their precedence decides which operation will be performed first. We have many different types of expressions in Python. Constant Expressions: These are the expressions that have constant values only. Example Output x = 15 + 1.3 16. print(x) Arithmetic Expressions: An arithmetic expression is a combination of numeric values, operators, and sometimes parenthesis. The result of this type of expression is also a numeric value. The operators used in these expressions are arithmetic operators like addition, subtraction, etc. Example Output x = 40 52 y = 12 28 add = x + y 480 sub = x - y 3. pro = x * y
div = x / y print(add) print(sub) print(pro) print(div) Integral Expressions: These are the kind of expressions that produce only integer results after all computations and type conversions. Example Output a = 13 25 b = 12. c = a + int(b) print(c) as result after all computations and type conversions. Example Output a = 13 2. b = 5 c = a / b print(c) Relational Expressions: In these types of expressions, arithmetic expressions are written on both sides of relational operator (> , < , >= , <=). Those arithmetic expressions are evaluatedfirst, and then compared as per relational operator and produce a boolean output in the end.These expressions are also called Boolean expressions. Example Output a = 21 True b = 13 c = 40 d = 37 p = (a + b) >= (c - d) print(p) Logical Expressions: These are kinds of expressions that result in either True or False. It basically specifies one or more conditions. For example, (10 == 9) is a condition if 10 is equal to
- Know it is not correct, so it will return False. Studying logical expressions also come across some logical operators which can be seen in logical expressions most often. Example Output P = (10 == 9) False Q = (7 > 5) True R = P and Q True S = P or Q T = not P
Example Output age = “\n Please enter your age: ” Please enter your age: 17 You‟re not eligible to vote while True: Please enter your age: 18 age = input if age >= 18: break else: print (“You‟re not eligible to vote”)
Continue statement
The program encounters a continue statement in Python, it skips the execution of the current iteration when the condition is met and lets the loop continue to move to the next iteration. It is used to continue running the program even after the program encounters a break during execution. Example Output for letter in 'Flexible': Letters: F if letter == ' ': Letters: l continue Letters: e print ('Letters: ', letter) Letters: x Letters: i Letters: b Letters: l Letters: e
Pass statement
The pass statement is a null operator and is used when the programmer wants to do nothing when the condition is satisfied. This control statement in Python does not terminate or skip the execution, it simply passes to the next iteration. Example Output for letter in 'AvsCollege': Letters: A if letter == 'x': Letters: v pass Letters: s print ('Letters: ', letter) Letters: C Letters: o Letters: l Letters: l Letters: e Letters: g Letters: e
Selection Statement
In Python, the selection statements are also known as decision making statements or branching statements. The selection statements are used to select a part of the program to be executed based on a condition. Python provides the following selection statements.
- if statement
- if-else statement
- if-elif statement
if statement in Python
Example Output a = 20 ; b = 20 a and b are equal if ( a == b ): If block ended print( “a and b are equal”) print(“If block ended”) In Python, use the if statement to test a condition and decide the execution of a block of statements based on that condition result. The if statement checks, the given condition then decides the execution of a block of statements. If it is True, then the block of statements is executed and if it is False, then the block of statements is ignored. The execution flow of if statement is as follows.
Example Output i = 10 i is smaller than 15 if (i == 10): i is smaller than 12 too
First if statement
if (i < 15): print("i is smaller than 15")
Nested - if statement
Will only be executed if statement above
it is true
if (i < 12): print("i is smaller than 12 too") else: print("i is greater than 15")
if-elif-else Ladder
The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will beexecuted.
Example Output print(“Select your ride:”) Select your ride: print(“1. Bike”) 1. Bike print(“2. Car”) 2. Car print(“3. SUV”) 3. SUV 3 choice = int( input() ) if( choice == 1 ): print( “You have selected Bike” ) elif( choice == 2 ): print( “You have selected Car” ) elif( choice == 3 ): print( “You have selected SUV” ) else: print(“Wrong choice!“)
Python While Loop
You have selected SUV Python While Loop is used to execute a block of statements repeatedly until a given condition is satisfied. And when the condition becomes false, the line immediately after the loop in the program is executed.
