Python Basics: Operators, Expressions and Control Flow

Question 1

What do computers do?

Answer 1

1. They perform calculations
   - -> that are built into the computer’s language
   - -> That you as the programmer define
2. Remembers results
3. Computers only do what you tell them

Question 2

What is declarative knowledge?

Answer 2

A statement of facts.

i.e. A student must pass 3 out of 5 mandatory assignments to qualify for the exam

Question 3

What is imperative knowledge?

Answer 3

“How to…“/Recipe:

• Sequence of simple steps
• Flow of control process that specifies when each step is executed
• information when to stop
  i. e.
  1. A student takes a mandatory assignment and works on it
  2. He uploads the solution before the deadline
  3. Teacher will grade and let them know if they passed or failed
  4. Repeat the above procedure 5 times
  5. See if the student passes or fails the course

Question 4

What is a fixed program computer?

Answer 4

A computer that will solve a specific mathematical problem but nothing else i.e. calculator

Question 5

What is a stored program computer?

Answer 5

The computer stores and executes instructions (certain elements of the computer will execute the instructions in a specific sequence)

Question 6

What are the three main parts in a basic machine architecture?

Answer 6

Memory
Control Unit
Arithmetic Logic Unit

Question 7

What is a syntax?

Answer 7

The structure of statements in a computer language:
i.e. “hi” 5 not valid
but 3.2 * 5 is valid

Question 8

What are semantics?

Answer 8

the meaniing of a syntactically correct string of symbols with no static semantic errors.

Caution: such strings only have one meaning in programming languages

Question 9

What are different syntactic/semantic errors?

Answer 9

1. Syntactic errors
   - -> common and easily found (IDE shows them)
2. Static semantic errors
   - -> some languages check for them before running a program
   - -> can cause unpredicted behavior
3. No semantic error but different meaning than what programmer intended
   - -> program crashes
   - -> runs forever
   - -> gives an outcome but different than what was expected

Question 10

What is the difference between interpreted and compiled?

Answer 10

1. Compiled languages are first converted into machine-readable code that the processor can execute (faster and more efficient than interpreted languages, better control over memory and CPU usage) i.e. C, C++
2. Executed directly –> Interpreters run a program line by line and execute command one by one , often easier to debug as interpreter can produce error messages that are easy to set into relation with the code
   i. e. Pytho, JavaScript

Question 11

What is a (Python) Program?

Answer 11

1. A program is a sequence of definitions and commands
   - -> definitions are evaluated and commands executed by the python interpreter
2. Command statements instruct the interpreter what to do
3. Programs can be directly typed into a shell or stored in a file that is read into the shell and evaluated

Question 12

What are data objects?

Answer 12

1. An instance of a data type (The type defines what the program can do with them)
2. Programs manipulate data objects
3. Objects are
   - -> scalar (can be subdivided)
   - -> non-scalar (have internal structure that can be accessed)

Question 13

Name a few scalar objects?

Answer 13

int, float, bool, double, NoneType

Question 14

What is an expression?

Answer 14

1. Expressions combine objects and operators
2. Has a value
3. Syntax: object operator object

i.e. + (Sum), - (Difference), * (Product), / (Division), %(Remainder), ** (power of)

Question 15

How do you bind variables and values?

Answer 15

Using the equal sign

pi = 3.14159

Question 16

Why do you give names to values of expressions?

Answer 16

To reuse the names instead of computing the values every time you need them
i.e. pi = 3.14159
radius = 2.2
area = pi * (radius ** 2)

Question 17

What happens if you change bindings?

Answer 17

1. You can rebind variable names using new assignments

2. Previous value may still be stored but you cannot access it anymore

Question 18

What is a String?

Answer 18

1. Sequence of characters (i.e. letters, special characters, spaces, digits)
2. enclosed in quotation marks or single quotes “”, ‘’
3. You can concatenate strings using +: greeting = hi + “ “ + name

Question 19

How can you input something=

Answer 19

use the input function

–> value is by default always a string so you must cast with numbers when needed i.e. int(input(“Type a number…))