Chapter 2 Introduction to Python

objects, operators, expressions, values

Objects and operators can be combined to form expressions, each of which evaluates to an object of some type. The value of the expression.

+, -, *, //, /, %, **

are arithmetic operators

machine code

are instructions written in binary or hexadecimal and is code that the computer can respond directly to.

floating point numbers

are numbers represented as such, 3.0, 4.5, 6.6

non-scalar

are objects that have internal structure

scalar

are objects that indivisible

repetition operators

are operators which take a string and multiply them. 2 * John = johnjohn

straight-line programs

are programs that execute one statement after another in the order in which they appear, and stop when they run out of statements

objects

are the core things that is manipulated

keyword list

as, assert, break, class, continue, def, del, elif, else, except, false, finally, for, from, global, if, import, in, is, lambda, nonlocal, none, not, or, pass, raise, return, true, try, while, with, yield

and, or, not

boolean operators

type checking

checks the type on an object

concatenation

combines 2 strings together

>, >=, ==, !=, <, <=

comparison operators

branching

contain at least one conditional statement which can reduce the length of runtime of a program but not increase the length of runtime.

type

defines the kinds of things that programs can do with an object

function: len()

determines the length of a string

compound boolean statement

evaluates two or more expressions in the conditional

conditional

has 3 parts: a test which evaluates an expression to either true or false. a block of code that is executed if the test evaluates to true an optional block of code that is executed if the test evaluates to false

reserved words / keywords

have bult-in meanings and cannot be used as a variable

conditional statement construct

if boolean statement: block of code else: block fo code

command / statement

instructs the interpreter to do something

Python Scalar Objects

int, float, bool, none

types

int, str, float

interpreted vs. compiled

interpreted programs is executed directly are easier to debug because the error messages are correlated to the source code, while compiled programs are first converted into a sequence of machine-level primitive operations, use less space, and run more quickly.

nested

is a conditional statement, within another conditional statement(s). The inner most is evaluated first

Python

is a general-purpose programming language that can be used effectively to build almost any kind of program that does not need direct access to the computer's hardware. It is not optimal for programs that have high reliability constraints, because of weak static semantic checking, or that are built and maintained by many people or over a long period of time. It is a simple language to learn. It is designed to be interpreted, it can provide the kind of runtime feedback that is especially helpful for new programmers. It has a large number of libraries that interface with Python.

low-level language

is a language that we program instructions and data objects at the level of the machine

high-level language

is a language using more abstract operations that have been provided by the language designer

program / script

is a sequence of definitions and commands

assignment

is a statement which associates the name to the left of the = symbol with the objet denoted by the expression to the right of the =.

integrated development environment (IDE)

is a text editor for writing code in.

variables

is a way to associate a name with an object

looping

is a way to iterate. it begins with a test, if it evaluates true, then the program executes a loop, and reevaluates the test. this is repeated until the test evaluates false

indentation

is semantically meaningful. Requires 4 spaces

constant time

is the maximum running time bounded by the length of the program is said to run

expressions

is the result of combining objects and operators

value

is the result of combining objects and operators

shell prompt

is the symbol >>>

type conversions / type casts

is used to convert one type of an object to another type

function: type()

is used to determine the type of an object

slicing: string[start:stop:step]

is used to extract substrings of arbitrary length

function: input()

is used to get input directly from a user

hand-simulating

is using paper and pencil to simulate the code

variable names

it's just a name, nothing more

PEMDAS

order of operations: Parentheses, Exponents, Multiplication, Division, Addition, Subtraction

targeted programming language

refers to primitive operations are targeted or fine-tuned to a specific domain

general programming language

refers to whether the primitive operations are widely applicable

source code

sequence of instructions written by a programmer

overloaded

some operators have different meanings depending upon the types of the objects to which it is applied

binds

takes a name and connects it to an object

break

terminates the loop in which it is contained

shell

the location where definitions are evaluated and the commands are executed by the interpreter.

computation complexity

the study of the intrinsic difficulty of problems

variable name style

they can be upper or lower case, have digits and a special character _. Names are case sensitive, must not start with a digit. See the Python Style Guide for more information

comments

used to enhance readability and inform the programmers later what the intentions of the code were.

indexing: string[x]

used to extract individual characters from a string

function: print()

used to print something as output

operators

when combined with operators form expressions

iteration

when you want the code to the same thing over and over again

function: while statement

while (expression != True): block of code optional counter statement