Programming
and databases

Joern Ploennigs

Operators

Midjourney: Caligraphic Equations

Recap: In-Class Question

What levels does the knowledge pyramid have?

Midjourney: Tower of Babel

Review: Knowledge Pyramid

The knowledge pyramid is a model for representing the emergence of knowledge.

The four element types: Signs, Data, Information, and Knowledge are represented as four levels of a pyramid.

Signs form the base and knowledge the apex of the pyramid.

Review: Lecture Hall Question

What data types are there in programming languages?

DALL·E 2: A chair in the shape of a avocado

Wiederholung: Datentyp

The data type specifies what kind of data it describes (data contract) and which operations can be performed on it.

Review: In-class Question

What data types are there in Python?

Midjourney: A python programming a robot

Recap: Data Types - Python

Python simplifies some data types.

Process

Instructions

• 📘 Definition: Statement

  A statement is a single instruction formulated in the syntax of a programming language that is executed sequentially in the program.

• 📘 Definition: Expressions

  A special form of statements are expressions, which always return a value and thus have a data type.

• 📘 Definition: Operator

  An operator is a part of expressions and is a symbol or keyword that tells the compiler or interpreter to perform a specific operation on values.

• Example: In a simple variable assignment, the expression appears to the right of the assignment operator =.

  VariableName = Expression
  

Arithmetic Operators

Arithmetic operators perform the standard mathematical operations. They are used with numeric values to perform general mathematical operations.

Operator	Example	Effect
Addition	x + y	10 + 3 (Result: 13)
Subtraction	x - y	10 - 3 (Result: 7)
Multiplication	x * y	10 * 3 (Result: 30)
Division	x / y	10 / 3 (Result: 3.33)
Integer Division	x // y	10 // 3 (Result: 3)
Modulo Operator	x % y	10 % 3 (Result: 1)
Exponentiation	x ** y	10 ** 3 (Result: 1000)

Assignment Operators

Assignment operators assign values to variables. Python uses augmented assignment for all arithmetic operations; however, there is no increment or decrement like in other languages.

Operator	Example	Effect
Assignment	x = y	Variable x receives the value y
Augmented addition	x += 4	x = x + 4 # Variable x is increased by 4
Augmented multiplication	x *= 4	x = x * 4 # Variable x is multiplied by 4
Augmented division	x /= 4	x = x / 4 # Variable x is divided by 4
Augmented floor division	x //= 4	x = x // 4 # Variable x is floor-divided by 4
Augmented modulo	x %= 4	x = x % 4 # The remainder of dividing variable x by 4

Comparison Operators

Comparison operators compare two values and return true or false as a result. For example, a == b tests whether a is equal to b, and returns true or false accordingly, while a != b tests whether a is not equal to b.

Operator	Example	Effect
Equals	x == y	true if x is equal to y
Not equal	x != y	true if x is not equal to y
Greater than	x > y	true if x is greater than y
Less than	x < y	true if x is less than y
Greater than or equal to	x >= y	true if x is greater than or equal to y
Less than or equal to	x <= y	true if x is less than or equal to y

Identity Operators

Identity operators compare objects. For example, if x = [1, 2, 3] holds, i.e., x is a list, then type(x) is list evaluates to true, and type(x) is not list is false. They check whether two objects refer to the same memory location. x is y returns true when both variables refer to the same object, i.e., point to the same memory location.

Operator	Example	Effect
Is	x is y	true if both variables refer to the same object.
Is not	x is not y	true if the variables do not refer to the same object.

Lecture hall question

What outcomes do you get for each logical operation?

(Corresponds to propositional logic)

Logical operations

Lecture Hall Question

What results are there for each logical operation?

(Corresponds to propositional logic)

Logical Operations

Logical Operators

Logical operators combine boolean expressions, which are then evaluated as true or false. For example, here the variable is_teenager = (alter > 13) and (alter < 19) is evaluated as true when the value of the variable alter is equal to 14.

P and Q stand for logical expressions, e.g. P = (x > 10) and Q = (x < 20).

Operator	Example	Effect
Logical AND	P and Q	Returns true (1) if both expressions P and Q are true.
Logical OR	P or Q	Returns true (1) if either expression P or Q is true.
Logical NOT	not P	Negates the expression P: true becomes false, false becomes true.

Bitwise Operators

Bitwise operators perform bitwise operations on integer operands. In other words, the operands are converted to their binary representations, e.g., x = 5 = 0101, y = 3 = 0011, and then each bit in operand x is combined with the bit at the corresponding position in operand y.

| Operator | Example | Effect | | --------- | --------- | ------- | | Bitwise AND | x & y | The resulting bit is 1 if both bits are 1. | | Bitwise OR | x | y | The resulting bit is 1 if at least one of the bits is 1. | | Bitwise XOR (Exclusive OR) | x ^ y | The resulting bit is 1 if exactly one of the bits is 1. | | Bitwise NOT | ~x | Returns the one's complement of x. | | Right shift | x >> n | The bits in x are shifted to the right by n positions. | | Left shift | x << n | The bits in x are shifted to the left by n positions. |

Membership operators

Membership operators check whether an object is a member of a list, e.g., 4 in [1,2,3] checks whether 4 is contained in the list.

x here stands for an arbitrary object, and list for a collection.

Operator	Example	Effect
in	x in list	True if x is in the list list.
not in	x not in list	True if x is not in the list list.

Questions?

programmierung
und datenbanken