1. for a 2d list:

# Creates a 2 x 5 matrix [[ num for _ in range(col)] for _ in range(row)]

Matrix = [[0 for y in xrange(5)] for x in xrange(2)]

2. list vs tuple

space: tuple is smaller

tuple has hash function for map

tuple can't change!

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old detailed notes:

# List!

just a collection of grouping of items, which is a data structure

1.list

[] tells python it is a list, seperate by ","

it can contain any type in the same list

demo_list = ["a", 1, 45.7, True] #no error!

use len funtion to check how many item is in the list

len(demo_list) #4

#another way to build a list -- list() function

tasks = list(range(1,4))

2.access value in list

list always start counting at zero

friends = ["AZ", "Dood"]

print(friends[0]) # AZ

print(friends[3]) # error, list index out of range

print(friends[-1) # AZ negative value also work! 倒着数！，-1和0是一样的

>>> "Az" in friends

# True 可以check是不是在list里

code people[-1][0]=="A" not working, because in Python, strings are immutable;Basically, an object that is immutable cannot be modified once it is created unlike lists which are "mutable".

3. iterate through a list

#for loop, while loop

nums = [1,2,3,True,8.15]

for num in nums

print(num)

OR

nums = [1,2,3,True,8.15]

i = 0

while i < len(nums):

print(nums[i])

i += 1 #python 里没有i++！！

4. List Method - add stuff

(method is not the same thing as function, method is the one needs object to use?)

data = [1,2,3]

----data.append("purple) # append can only add ONE element to the end

----use extend to add more elements to the end of list

list1 = [1,2,3,4]

list1.append([5,6]) #list1: [1,2,3,4,[5,6]]

list1.extend([5,6]) #list1:[1,2,3,4,5,6]

more example:

#注意这个例子里的list2 是list1里面的浅拷贝，所以改变list2的时候list1也变了！

list1 = [1,2,3,4]

list2 = list1

list1.append([5,6]) #list1: [1, 2, 3, 4, [5, 6]]

print(list1)

list2.extend([5,6])

print(list2) #list2:[1, 2, 3, 4, [5, 6], 5, 6]

print(list1) #list1:[1, 2, 3, 4, [5, 6], 5, 6]

# list2.extend(7,8) #extend only take one argument as append

# print(list2)

----insert（the pos you want to insert, val to insert）

eg:

list1 = [1,2,3,4]

list1.insert(3,8) #list1: [1, 2, 3, 8, 4]

print(list1)

list1.insert(-2, "hi")

print(list1) #还是在该index处（前）插入 --list1:[[1, 2, 3, "hi",8, 4]---calculate the position based on old array

list1.insert(len(list1), "last")

print(list1) #list1:[1, 2, 3, "hi",8, 4, "last"]

5. list method -remove stuff

stuff_list.clear() #delete everything (became an empty list)

pop() #remove the item at the given position in the list and return it

#if no index is specified, removes and returns last item in the list

list1.pop() # "last"

list1.pop(1) # 2

print(list1) #[1, 3, 'hi', 8, 4]

remove #move the first value found and give a error if not found

list1.remove(1)

print(list1) #[3, 'hi', 8, 4]

6. list method

index() #return the index of the specified item in the list

#can specify start and end, check start from start (val, start_index, end_index)

count() # how many it shows in the list

#if not will be 0

reverse()

#IN PLACE! reverse the elements of the list - update your origin list

sort()

#IN-PLACE！ asending order

join()

#actually a string method, not a list method --- always used with strings and lists

words = ["today", "is", "good!"]

" ".join(words) #will put a space in every one of the list element --- "today is good!"

#result is also a string

name = ["Mr", "Lee"]

res = ".".join(name)

print(res) # Mr.Lee

7. slicing!

#give me a part of list!

#make new lists using slices of the old list!

some_list[start: end: step]

#start: where want it to begin ---will need at least one :! to show it is slice

list3 = list1[1:] # starts from 1 ['hi', 8, 4]

print(list3)

list4 = list1[-3:] # starts from -3 ['hi', 8, 4]

print(list4)

list1[0:] #give you a copy of the list, but not the same origin one! unique copy, own address!

# the end index is exclusive! the end is not included

list5 = list1[1:3] # starts from 1, end at 2 ['hi', 8]

print(list5)

#if negative nums, is item to exclude from the end

list6 = list1[1:-1] # starts from 1 end at 2['hi', 8]

print(list6)

#step: similar as step with range

list7 = [1,2,3,4,5,6]

list8 = list7[::2]

print(list8) #[1, 3, 5] --start from the beginning

list9 = list7[1::2]

print(list9) #[2, 4, 6] --start at index 1

#with negative numbers, reverse the order

list10 = list7[1::-1]

print(list10) # [2, 1] 从 index是1开始，倒着数到boundary

list11 = list7[2::-1]

print(list11) # [3, 2，1] 从 index是1开始，倒着数到boundary

list12 = list7[:1:-1]

print(list12) # [6, 5, 4, 3] 倒着数到不包括index是1的那些

8.tricks with slices

-reverse list/strings #don't forget this way give you a copy, but the reverse() is in-place

reverse string: string[::-1]

numbers = [1,2,3,4,5]

numbers[1:3] = ["a","bac"]

print(numbers) #[1, 'a', 'bac', 4, 5] #list is muatable in python

9.swap value with comma syntax (for shuffling/sorting/algorithm)

color = ["pink" , "yellow"]

color[0],color[1] = color[1], color[0]

print(color) #['yellow', 'pink']

10.list comperhesion

#[___for ___ in ___] ---output another list(list! even if input is a string, still give you list)

nums = [1,2,3]

tenthNums = [x *10 for x in nums]

print(tenthNums)#[10, 20, 30]

name = "lee"

up_name = [char.upper() for char in name]

print(up_name) #['L', 'E', 'E']

truth = [bool(val) for val in [0,[],'',1]]

print(truth) #[False, False, False, True]

#convert a list of nums to a list of strings

string_list = [str(num) for num in nums]

print(string_list) #['1', '2', '3']

numbers = [1,2,3,4,5,6]

evens = [num for num in numbers if num % 2 == 0]

odds = [num for num in numbers if num % 2 != 0]

print(evens) #[2, 4, 6]

print(odds) #[1, 3, 5]

manip = [num *2 if num % 2 == 0 else num/2 for num in numbers]

print(manip)

#a good one!

with_vows = "This is so much fun!"

without_vows = "|".join([chars for chars in with_vows if chars not in "aeiou"]) #remember, join() return a string

print(without_vows) #T|h|s| |s| |s| |m|c|h| |f|n|!

without_vows2 = "".join([chars for chars in with_vows if chars not in "aeiou"]) #remember, join() return a string

print(without_vows2) #Ths s s mch fn!

print("......".join(["hi", "?"])) #hi......?

answer = [num for num in [1,2,3,4] if num in [3,4,5,6]] #num needs to be in both list

answer2 = [name[::-1].lower() for name in ["Elie", "Tim", "Matt"]] # get the lower case and reverse it

answer = [num for num in range(1,101) if num % 12 == 0] #get all numbers in 1-100 which is divisible by 12

answer = [chars for chars in "amazing" if chars not in "aeiou"] #kick out vowels!

11.nested list -- for matricies

nested_list = [[1,2,3],[4,5,6],[7,8,9]]

#access it

nested_list[0][1] #2

nested_list[-1][-2] #8

#have to use nested loops to iterate elements

for va in nested_list:

for val in va:

print(val)

#nested list comprehension

[[print(val) for val in va] for va in nested_list]

board = [[num for num in range(1,4)] for val in range(1,4)]

print(board) #[[1, 2, 3], [1, 2, 3], [1, 2, 3]]

start_up = [["x" if num % 2 != 0 else "o" for num in range(1,4)] for val in board] # 前一个[]的就是val了，不需要declare

print(start_up) #[['x', 'o', 'x'], ['x', 'o', 'x'], ['x', 'o', 'x']]