0.GUI (graphical user interface) such as file finders

eg sed 's/dude/Colt/g' report.txt > report_new.txt //sed:search and pop it to report_new

Be familiar and confortable with command line

file structure is a tree, all relative to a base ROOT director

root/

each additional level down adds a "/"

absolute path /Users/colt // abs path always start with a / --which stands for the root

by default is at home directory and represent as "~"

pwd : print working directory

cd : change directory

type python3 to go into python3, otherwise is python --2

use touch to create a new .py file

print("hello world")

//don't need the semi colon at end

1.variables must stary with a letter or underscore_

CASE sensitive!!

2. ** power

% remainder

/ 不是整数除法，就是正常的除 （in python 3） python2 和 c++一样还是整数除法

x = 1 + 2**3/4*5

print(x) //1+8/4 *5 =1+2*5 =11.0

1+1.0 // 2.0 - to float automatically

// --- Interger Division

5//3 #1

10//3 #3 (always round down)

1/2 #0.5 python always get float

2**3 #8

49**0.5 #7

13%2 #1

3.constans:fixed vlues such as numbers, letters and strings are constants

string constants use single quotes ('') or double quotes ("")

4. try/except -- traceback

try 里面任意一个die了直接走except，不会继续走下面的了--利用try来尝试危险，catch errors

astr = ‘hello bob'

try:

ister = int (astr)

except:

ister = -1 // usualy provide hints for where is wrong, can add a quit here

5.

name = input('who are u?) // the input() will return a string

print ('welcome', name) // the comma will creat a space

6. use # for comments in python

7. python use indent to distinguish block, which is 4 spaces, it is better to use space than tab, to avoid difference between different editors

8. python 里的print（） 有自动换行功效

use --type(9)

will show the type of it, can be a variable name

9.

python documentation ---docs.python.org

Give you information about python stuff--make sure to check the python3 documents

''' for python multiple line comments

#the naming convention of python is s_n_a_k_e

#you don't need to declare the type of variables

nums_of_casts = 99

nums_of_casts * 2 #nums_of_cats doesn't change

all, at, once = 5, 10, 15

#you can always assign and reassign variables

10. naming_conventions in python

most variables should be lower case,

CAPITAL_NAME usually is constants

UpperCamelCase : refer to a class

"dunder" for double underscore ***

11.Some data types:

bool (True, False, the first case has to be capital)

int

str (a sequence of Unicode chars， “ ” or ‘’)

list（an ordered sequence of values of other data types [1,2,3])

dict ( a collection of key: values e.g. {"first_name":"Le", "last_name": "Lei"}

12. Dynamic typing

you can reassign variables to different types

dynamic typing vs statically-typed(variables are stuck with their originally-assigned types)

13. None (case sensitive!)

(python version of NULL)

can set new stuff with None if we haven't assign it

(want a container, but nothing here, and the type of None is Nonetype--only itself)

14.Declaring strings

doesn't matter if single or double, but better to stay it consistant

msg = "he said "hello there !"" --- error, python read it "XX" +YY""

msg2 = "he said 'hello there !'" --- good

msg3 = 'he said "hello there !"' --- good

15.escape sequence

str_sth = "he said \"ha ha\"" --- good #str is never a good variable name, which you could..

16. string concateration

with “ +”

user = "blue Boy"

print("hello there" + user) # hello therebuleBoy ---不会自动给你加空格

8 + "hello" #error!

guess = 9

print("your guess is" + guess) #error!

name = "col"

name += "S" # name now = colS #also works for numbers

17.string format

interpolate #插入

f-strings (python 3.6+)

x = 10

formatted = f"I told you {x} times!" #不可以忘了这个f！

#you can also do math in the {}

# in python 2 .format() --play ground only support it

print("the {} is ).format(sth)

first = "Colt"

last = "Steele"

formatted = "First Name: {}, Last Name: {}". format(first, last) #可以直接在string 后加

18. every stirng is indexed, started with 0

"lol"[0] #l

name = "Chuck"

name[5] # error! max index is 4 ; not counting '\0' (if there is one in python)

name[-1] #k

name[-2] #c 倒着数的嗷

19. convert data types

in string interpolation, data type are implicitly converted into string form

you can explicitly convert type by var2 = type (var1)

deci = 12.213

interger = int(deci) #12

my_list = [1,2,3]

my_list_as_string = string(my_list) # "[1,2,3]"

1/3 ----0.3333

int(99.99) #99 only truncate not around

4/2 ----2.0

round(thing to round, how many decimal points)

20.for input function, 不会自动换行

data = input("what is your name?") # what is your name?your_input (also no space!)

print("You said" +data)

#onther way looks nicer

print("what is your name?")

data = input() # what is your name? -another line- your_input

print("You said" +data)

21. conditional statements

if name == "tony stark :

use indent to distinguish

print("you are Iron Man")

elif name == "Peter Parker": #you can have multiple elif, but only one else

print("you are Spider Man")

elif name == "Natasha":

print("you are Black Widom")

elif name == "Thor":

print("you are Thor")

else :

print("you are Norm Man")

------

#这种没有之后的内容（indent的话会报错）

if name == "tony stark :

print("you are Iron Man")

22. Truthiness

things are natually false: empty objects, empty strings, None, and zero

animal = input("say sth)

if animal: #没有input时自动不会做这些

print("you said sth)

== test if they have the same value

"A" < "a" # yep

logical operators:

and, or(binary), not(unary)

age > 2 and age < 8

if not isWeekend():

do th

if not x or y: #先判断not X， 再看 or

do th

23.is vs ==

is check with the memory and == checks value

is--checking equality

a = 1

a == 1 #True

a is 1 #True

a = [1,2,3]

b = [1,2,3]

a == b #True

a is b #Flase, they are different objects

c = b

b is c #True, b and c are pointing to the same stuff

a = 13

b = 13

a == b #True

a is b #True

24. loop

-iterable objects

[40,30,435]

"hello'

range(1,10) # generate 1-9 包左不包右

for item in iterable_object:

do sth with item

eg:

for char in "hello":

print(char *10) #每个char 会print 10 次

for x in rang(1,10):

print x # print 1-9, BTW, python 的print会自动换行

25. ranges （commonly use for for loops）

range (7) # 0-6

range(1,8) #1-7 永远最右侧的不包

range(1,10,2) # give odd 1,3,5,7,9 - the last one is 间距

range(7,0,-1) #7-1

list(range(10)) #ok

tricky:

>>> nums = range(1,5)

>>> print(nums)

#range(1, 5)

26. while loop

while bool_expression:

do sth

for num in range(1,11):

print(num)

<=>

num = 1

while num < 11:

num += 1

print(num)

27.break

to exit out of a loop immediatly

28. style for python:

PEP8(style Guide for python code!)

autopep 8 --inplace ugly_code.py (need to install the package)