Travis Shen

Python Multi-line Statements

2018 年 6 月 2 日
Python

How python interpret multi-line code into single line code:

python program
physical lines of code(end with a physical newline CHARACTER create by enter)
logical lines of code(end with a logical NEWLINE token)
tokenized
execute

physical newlines vs logical newline

sometimes physical newlines are ignored in order to combine multiple physical lines into a single logical newline

break implicitly: [], (), {}

[1,

def my_func(a,

pass

break explicitly

if a \

and b \

and c:

pass

multi-line strings

multi-line strings are regular string, not comments (can be used as docstring)

escaped characters(\n, \t), non-visible characters(newlines, tabs) in multi-line are part of string; escaped characters will formatted when print it

ref:

https://github.com/fbaptiste/python-deepdive/blob/master/Part%201/Section%2002%20-%20A%20Quick%20Refresher/01%20-%20Multi-Line%20Statements%20and%20Strings.ipynb

Python Type Hierarchy

2018 年 6 月 2 日
Python

Number

Integral: Integer, Booleans
Non-Integral: Floats, Complex, Decimals, Fractions(1/3)

Collection

Sequences
- Mutable: List
- Immutable: Tuples, Strings
Sets
- Mutable: Sets
- Immutable: Frozen Sets
Mappings
- Dictionaries (relate to set)

Callables

Built-in Functions
User-Defined Fuctions
Instance Methods (e.g. len())
Built-in Method (e.g. my_list.append(x))
Generators
Classes
Class Instances(__call__())

Singletons

None
NotImplemented
Elipsis operators

When the browser, somewhere outside the JavaScript engine, has the event inside the JavaScript engine that want to be notified of, its get placed in the event queue, and WHETHER OR NOT the event have a function response to it.

The event queue gets looked at by JavaScript when the execution stack is EMPTY.

JavaScript engine is always running synchronously, what happening is that the browser is asynchronously putting things into event queue.

function waitThreeSeconds() {

var ms = 3000 + new Date().getTime();

while (new Date() < ms){}

console.log('finished function');

}

function clickHandler() {

console.log('trigger click event!');

}

document.addEventListener('click', clickHandler);

waitThreeSeconds();

console.log('finished execution');

log the result when double click while long run function(line 11) executed:

finished function

finished execution

trigger click event!

let in ES6

2018 年 6 月 2 日
JavaScript

let allows the JavaScript engine to use BLOCK SCOPING, means variables are only allowed inside specific block, such as if/else statement which defined by {}

Scope Chain

2018 年 5 月 29 日
JavaScript

While running a line of any execution context, if it can’t find a variable, it will look at OUTER ENVIRONMENT to look for that variable, somewhere down below in the execution stack. Which outer environment to look is depend on where this function sit LEXICALLY.

function b(){

console.log(myVar);

}

function a(){

var myVar = 2;

b();

}

var myVar = 1;

a();

/* it will log 1 when line 2 was executed,

because function b sits in global execution

context lexically, global execution context

is the outer environment to function b's

execution context

function a(){

function b(){

console.log(myVar);

}

b();

}

var myVar = 1;

a();

/* it will log 1 when line 4 was executed,

because function b sits in function a's execution

context lexically, funtion a sits in global

execution context, so it look for myVar in

variable enviroments in this order:

b()'s variable env => a()'s variable env => global variable env

Function Invocation and Execution Stack

2018 年 5 月 23 日
JavaScript

In the execution phase of global execution context, functions already setup in memory, when it execute function invocation command , such as someFunction(), a new execution context created and put to execution stacks (top of the stack). when function invocation finished, will popped of the stack

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