# 这是一个注释 
print("Hello, World!")

'''
这是多行注释，用三个单引号 
这是多行注释，用三个单引号  这是多行注释，
用三个单引号 
'''
print("Hello, World!")

"""
这是多行注释，用三个双引号
这是多行注释，用三个双引号 
这是多行注释，用三个双引号
"""
print("Hello, World!")

# 获取用户输入十进制数 
dec = int(input("输入数字："))  

print("十进制数为：", dec) 
print("转换为二进制为：", bin(dec)) 
print("转换为八进制为：", oct(dec)) 
print("转换为十六进制为：", hex(dec))

binary_number = '101010'
decimal_number = int(binary_number, 2)  # 二进制转换为十进制
octal_number = oct(decimal_number)    # 十进制转换为八进制
hexadecimal_number = hex(decimal_number)  # 十进制转换为十六进制

print('二进制数:', binary_number)
print('转换为十进制:', decimal_number)
print('转换为八进制:', octal_number)
print('转换为十六进制:', hexadecimal_number)

octal_number = '52'
decimal_number = int(octal_number, 8)      # 八进制转换为十进制
binary_number = bin(decimal_number)         # 十进制转换为二进制
hexadecimal_number = hex(decimal_number)    # 十进制转换为十六进制

print('八进制数:', octal_number)
print('转换为十进制:', decimal_number)
print('转换为二进制:', binary_number)
print('转换为十六进制:', hexadecimal_number)

hexadecimal_number = '2a'
decimal_number = int(hexadecimal_number, 16)   # 十六进制转换为十进制
binary_number = bin(decimal_number)             # 十进制转换为二进制
octal_number = oct(decimal_number)              # 十进制转换为八进制

print('十六进制数:', hexadecimal_number)
print('转换为十进制:', decimal_number)
print('转换为二进制:', binary_number)
print('转换为八进制:', octal_number)

var1 = 'Hello World!' 
var2 = "Python Runoob"  

print(var1[0]) 
# H
print(var2[1:5])
# ytho

print('C:\some\name')  
# 这里\n的意思是换行
# C:\some
# ame
print(r'C:\some\name')  
# 这里\n不会转义
C:\some\name

print("My name is %s and weight is %d kg!" % ('Zara', 21))
# My name is Zara and weight is 21 kg!

s = """My Name is Pankaj.
I am the owner of JournalDev.com
JournalDev is a very popular website in Developers community."""

print(s)
# My Name is Pankaj.
# I am the owner of JournalDev.com
# JournalDev is a very popular website in Developers # # community.

sql = "select * " \
" from a " \
" where b = 1"

print(sql)
# select * from a  where b = 1

sql = ("select *"
" from a "
" where b = 1")

print(sql)
# select * from a  where b = 1

name = "Ada Lovelace" 
print(name.title()) # Ada Lovelace
print(name.upper()) # ADA LOVELACE 
print(name.lower()) # ada lovelace

favorite_language = ' python '
favorite_language.rstrip() # ' python'
favorite_language.lstrip() # 'python ' 
favorite_language.strip()  # 'python'

str="1011011"
print(str.count('0'))
## 2

str = "this is string example....wow!!!" 
print (str.split( ))       # 以空格为分隔符 
print (str.split('i',1))   # 以 i 为分隔符分割一次
print (str.split('w'))     # 以 w 为分隔符

# ['this', 'is', 'string', 'example....wow!!!']
# ['th', 's is string example....wow!!!']
# ['this is string example....', 'o', '!!!']

url = "http://www.baidu.com/python/image/123456.jpg"
path = url.split("/")
print(path[-1])
# 123456.jpg

str = "www.w3cschool.cc"
print(str.replace("w3cschool.cc", "runoob.com"))  )
# www.runoob.com

str = "is is is is" 
print(str.replace("is", "was", 3))
# was was was is

str1 = "Runoob example....wow!!!" 
str2 = "exam";  
print(str1.find(str2)) 
# 7
print(str1.find(str2, 10))
# -1

s1 = "-"
s2 = ""
seq = ("r", "u", "n", "o", "o", "b") 

print(s1.join( seq ))
# r-u-n-o-o-b
print(s2.join( seq ))
# runoob

str1 = "runoob2016"  
print (str1.isalnum())
# True

str2 = "23443434"
print (str2.isnumeric())
# True

"{} {}".format("hello", "world")    
# 不设置指定位置，按默认顺序 
# 'hello world'  

"{0} {1}".format("hello", "world")  
# 设置指定位置 
# 'hello world'  

"{1} {0} {1}".format("hello", "world")  
# 设置指定位置 
# 'world hello world'

print("网站名：{name}, 地址 {url}".format(name="菜鸟教程", url="www.runoob.com"))
# 网站名：菜鸟教程, 地址 www.runoob.com

# 通过字典设置参数
site = {"name": "菜鸟教程", "url": "www.runoob.com"}
print("网站名：{name}, 地址 {url}".format(site))
# 网站名：菜鸟教程, 地址 www.runoob.com

# 通过列表索引设置参数
my_list = ['菜鸟教程', 'www.runoob.com']
print("网站名：{0[0]}, 地址 {0[1]}".format(my_list))  # "0" 是必须的
# 网站名：菜鸟教程, 地址 www.runoob.com

print("{:.2f}".format(3.1415926))
# 注意返回的是字符串
# '3.14'

print ("{} 对应的位置是 {{0}}".format("runoob"))
# runoob 对应的位置是 {0}

name = 'Runoob'
print(f'Hello {name}')  # 替换变量
# 'Hello Runoob'
print(f'{1+2}')     # 使用表达式
# '3'

w = {'name': 'Runoob', 'url': 'www.runoob.com'}
print(f'{w["name"]}: {w["url"]}')
# 'Runoob: www.runoob.com'

list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5 ]
list3 = ["a", "b", "c", "d"]
list4 = list(('foo','bar','baz'))

gen = range(10)
print(list(gen))
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5, 6, 7]
 
list1[0]      # physics
list1[2:]      # [1997, 2000]
list2[1:5]    # [2, 3, 4, 5]
list2[:]      # [1, 2, 3, 4, 5, 6, 7]
list2[-1]     # 7

seq = [7, 2, 3, 6, 3, 5, 6, 0, 1]
seq[:5]
# [7, 2, 3, 6, 3]
seq[-4:]
# [5, 6, 0, 1]

seq[::2]
# [7, 3, 3, 6, 1]

seq[::-1]
# [1, 0, 6, 5, 3, 6, 3, 2, 7]

motorcycles = ['honda', 'yamaha', 'suzuki'] 
motorcycles.append('ducati')  
# ['honda', 'yamaha', 'suzuki', 'ducati']

motorcycles = ['honda', 'yamaha', 'suzuki'] 
motorcycles.insert(0, 'ducati') 
# ['ducati', 'honda', 'yamaha', 'suzuki']

aList = [123, 'xyz', 'zara', 'abc']
aList.insert(3, 2009)      
# [123, 'xyz', 'zara', 2009, 'abc']

motorcycles = ['honda', 'yamaha', 'suzuki'] 
del motorcycles[1] 
print(motorcycles)     # ['honda', 'suzuki']

aList = [123, 'xyz', 'zara', 'abc', 'xyz']
aList.remove('xyz')         
# [123, 'zara', 'abc', 'xyz']

aList = [123, 'xyz', 'zara', 'abc','xyz','xyz','xyz']
while True:
    if 'xyz' in aList:
       aList.remove('xyz')
    else:
        break
print(aList)
# [123, 'zara', 'abc']

motorcycles = ['honda', 'yamaha', 'suzuki'] 
popped_motorcycle = motorcycles.pop() 
print(motorcycles)        # ['honda', 'yamaha'] 
print(popped_motorcycle)  # suzuki

list1 = ['Google', 'Runoob', 'Taobao']
list_pop = list1.pop(1)
print(list_pop)         # Runoob
print(list1)            # ['Google', 'Taobao']

list1 = ['Google', 'Runoob', 'Taobao', 'Baidu']
list1.clear()
print (list1)
# []

list1 = ['Google', 'Runoob', 'Taobao'] 
list2 = list(range(5)) # 创建 0-4 的列表 
list1.extend(list2)  # 扩展列表 

print (list1)
# ['Google', 'Runoob', 'Taobao', 0, 1, 2, 3, 4]

# 语言列表 
language = ['French', 'English', 'German']  
# 元组 
language_tuple = ('Spanish', 'Portuguese')  
# 集合 
language_set = {'Chinese', 'Japanese'}  

# 添加元组元素到列表末尾 
language.extend(language_tuple)  
print(language)  
# ['French', 'English', 'German', 'Spanish', 'Portuguese']

# 添加集合元素到列表末尾 
language.extend(language_set)  
print(language)
# ['French', 'English', 'German', 'Spanish', 'Portuguese', 'Chinese', 'Japanese']

cars = ['bmw', 'audi', 'toyota', 'subaru'] 
cars.sort()
print(cars)    
# ['audi', 'bmw', 'subaru', 'toyota']

vowels = ['e', 'a', 'u', 'o', 'i']
vowels.sort(reverse=True)
print(vowels)  
# ['u', 'o', 'i', 'e', 'a']

b = ['saw', 'small', 'He', 'foxes', 'six']
#对列表按照元素的长度进行排序
b.sort(key=len)
print(b)
# ['He', 'saw', 'six', 'small', 'foxes']

aList = [123, 'xyz', 'zara', 'abc', 'xyz']
aList.reverse()
print(aList)        # ['xyz', 'abc', 'zara', 'xyz', 123]

cars = ['bmw', 'audi', 'toyota', 'subaru']
print(len(cars))      # 4

list1 = ['Google', 'Runoob', 'Taobao']
print(list1.index('Taobao'))
## 1

names = ['Bob','Tom','alice','Jerry','Wendy','Smith']
new_names = [name.upper() for name in names if len(name)>3]

print(new_names)
# ['ALICE', 'JERRY', 'WENDY', 'SMITH']

multiples = [i for i in range(30) if i % 3 == 0]
print(multiples)
# [0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

# 小括号
tup1 = ('physics', 'chemistry', 1997, 2000) 

# 内置函数tuple()
tup2 = tuple(('Python', 'Java', 'C#'))

# 任意无符号的对象，以逗号隔开，默认为元组
tup3 = "a", "b", "c", "d"

tup1 = ()
tup2 = tuple()

tup1 = (1,)
tup2 = (1)
print(type(tup1))
# <class 'tuple'>
print(type(tup2))
# <class 'int'>

print(tuple([4, 0, 2]))
# (4, 0, 2)

tup = tuple('string')
print(tup)
# ('s', 't', 'r', 'i', 'n', 'g')

tup = tuple(['foo', [1, 2], True])

tup[2] = False

# TypeError                                 Traceback (most recent call last)
# <ipython-input-10-c7308343b841> in <module>()
# ----> 1 tup[2] = False
# TypeError: 'tuple' object does not support item assignment

tup1 = (12, 34.56) 
tup2 = ('abc', 'xyz')  

# 创建一个新的元组 
tup3 = tup1 + tup2 

print(tup3)
# (12, 34.56, 'abc', 'xyz')

tup = tuple(['foo', [1, 2], True])
tup[1].append(3)
print(tup)
# ('foo', [1, 2, 3], True)

tup = ('physics', 'chemistry', 1997, 2000)  
del tup 

t = tuple(('Python', 'Java', 'C#'))
for item in t:
	print(item)
# Python Java C#

tup = (4, 5, 6)
a, b, c = tup
print(c)
# 6

tup = 4, 5, (6, 7)
a, b, (c, d) = tup
print(d)
# 7

seq = [(1, 2, 3), (4, 5, 6), (7, 8, 9)]
for a, b, c in seq:
    print('a={0}, b={1}, c={2}'.format(a, b, c))
    
# a=1, b=2, c=3
# a=4, b=5, c=6
# a=7, b=8, c=9

values = 1, 2, 3, 4, 5
a, b, *rest = values
print(rest)
# [3, 4, 5]

a, b, *_ = values

a = (1, 2, 2, 2, 3, 4, 2)
print(a.count(2))
# 4

a = (x for x in range(1,10))
>>> a
<generator object <genexpr> at 0x7faf6ee20a50>  
# 返回的是生成器对象

tuple(a)    # 使用 tuple() 函数，可以直接将生成器对象转换成元组
#(1, 2, 3, 4, 5, 6, 7, 8, 9)

tinydict = {'a': 1, 'b': 2, 'b': '3'}

print(tinydict['b'])
# '3'

tinydict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print(tinydict['Name'])
# Zara
print(tinydict['Age'])
# 7

tinydict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}  

tinydict['Age'] = 8 
# 更新 

tinydict['School'] = "RUNOOB" 
# 添加   

'Age' in tinydict	
# True

alien_0 = {'color': 'green', 'points': 5} 

del alien_0['points'] 

alien_0 = {'color': 'green', 'points': 5}
print(alien_0.pop('points'))
# 5
print('alien_0')
# alien_0

tinydict = {'Name': 'Runoob', 'Age': 7, 'Class': 'First'}  
tinydict.clear()     # 清空字典 
del tinydict         # 删除字典

user_0 = { 
  'username': 'efermi', 
  'first': 'enrico', 
  'last': 'fermi', 
 } 
 
for key, value in user_0.items(): 
	print(key, value)
    
# username efermi
# first enrico
# last fermi

favorite_languages = { 
 'jen': 'python', 
 'sarah': 'c', 
 'edward': 'ruby', 
 'phil': 'python', 
 }
 
for name in favorite_languages.keys():
# for name in favorite_languages:	
	print(name.title())  

favorite_languages = { 
 'jen': 'python', 
 'sarah': 'c', 
 'edward': 'ruby', 
 'phil': 'python', 
 } 
 
for language in favorite_languages.values(): 
     print(language.title())

d1 = {'a': 'some value', 'b': [1, 2, 3, 4], 7: 'an integer'}
d1.update({'b' : 'foo', 'c' : 12})
print(d1)
# {'a': 'some value', 'b': 'foo', 7: 'an integer', 'c': 12}

mapping = {}
for key, value in zip(key_list, value_list):
    mapping[key] = value

key = range(5)
value = reversed(range(5))
mapping = dict(zip(key,value))
print(mapping)
# {0: 4, 1: 3, 2: 2, 3: 1, 4: 0}

listdemo = ['Google','Runoob', 'Taobao']
# 将列表中各字符串值为键，各字符串的长度为值，组成键值对
newdict = {key:len(key) **for** key **in** listdemo}
print(newdict)
# {'Google': 6, 'Runoob': 6, 'Taobao': 6}

dic = {x: x**2 for x in (2, 4, 6)}

print(dic)
# {2: 4, 4: 16, 6: 36}

tinydict = {'Name': 'Runoob', 'Age': 7, 'Name': 'Manni'}  
print(tinydict['Name'])
# Manni

tinydict = {['Name']: 'Zara', 'Age': 7} 

print(tinydict['Name'])
 # TypeError: unhashable type: 'list'

tinydict = {'Name': 'Runoob', 'Age': 27}
print(tinydict.get('Age'))
# 27

# 没有设置 Sex，也没有设置默认的值，输出 None
print (tinydict.get('Sex'))  
# None

# 没有设置 Salary，输出默认的值  0.0
print (tinydict.get('Salary', 0.0))
# 0.0

runoob = {}
print(runoob.get('url'))     # 返回 None
# None

print(runoob['url'])     # 触发 KeyError
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# KeyError: 'url'

dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500}
keys = dishes.keys()

print(keys)
# dict_keys(['eggs', 'sausage', 'bacon', 'spam'])

print(list(keys))
# ['eggs', 'sausage', 'bacon', 'spam']

basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
print(basket)  

# 这里演示的是去重功能
# {'orange', 'banana', 'pear', 'apple'}

thisset = set(("Google", "Runoob", "Taobao"))
thisset.add("Facebook")

print(thisset)
# {'Taobao', 'Facebook', 'Google', 'Runoob'}

x = {"apple", "banana", "cherry"} 
y = {"google", "runoob", "apple"}  
x.update(y)   

print(x)
## {'banana', 'apple', 'google', 'runoob', 'cherry'}

fruits = {"apple", "banana", "cherry"}  

fruits.remove("banana")   
print(fruits)
# {'cherry', 'apple'}

fruits.remove("melon")  
#Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'melon'

fruits = {"apple", "banana", "cherry"}  
fruits.discard("banana")   
print(fruits)
# {'cherry', 'apple'}

fruits = {"apple", "banana", "cherry"}  
fruits.pop()   
print(fruits)
# {'apple', 'banana'} 也可能是 {'cherry', 'banana'} 或者 {'cherry', 'banana'}

thisset = set(("Google", "Runoob", "Taobao"))
print("Runoob" in thisset)
# True
print("Facebook" in thisset)
# False

a = {1, 2, 3, 4, 5}
b = {3, 4, 5, 6, 7, 8}

print(a.union(b))
# {1, 2, 3, 4, 5, 6, 7, 8}
print(a|b)
# {1, 2, 3, 4, 5, 6, 7, 8}

print(a.intersection(b))
# {3,4,5}
print(a & b)
# {3,4,5}

setnew = {i**2 for i in (1,2,3)}
print(setnew)
# {1, 4, 9}

a = {x for x in 'abracadabra' if x not in 'abc'}
print(a)
# {'d', 'r'}

sum = lambda arg1, arg2: arg1 + arg2
print(sum(10,20))
# 30

print((lamda a, b, c=5: a+b+c)(2,6))
# 13

str1 = '111'
str2 = '222'
print(str1,str2,sep='\n')

# 111
# 222

print(eval('2+2'))
# 4
data = ""

raw_data = "[{'姓名':'张三','年龄':14},{'姓名':'李四','年龄':25}]"
data = eval(raw_data)
print(data)
# [{'姓名': '张三', '年龄': 14}, {'姓名': '李四', '年龄': 25}]
print(type(data))  
# <class 'list'>

seasons = ['Spring', 'Summer', 'Fall', 'Winter']

print(list(enumerate(seasons)))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

print(list(enumerate(seasons, start=1)))   
# 下标从 1 开始
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

seq = ['one', 'two', 'three'] 
for i, j in enumerate(seq):    
	print(i, j)
# 0 one
# 1 two
# 2 three	

for element in enumerate(seq):
	print(element)
# (0, 'one')
# (1, 'two')
# (2, 'three')

some_list = ['foo','bar','baz']
mapping = {}
for i, v in enumerate(some_list):
	mapping[v] = i
print(mapping)
# {'foo': 0, 'bar': 1, 'baz': 2}

tmplist = filter(lambda n: n % 2 == 1, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) 
newlist = list(tmplist) 
print(newlist)
# [1,3,5,7,9]

str = "1 2 3 4 5"
num = str.split()

print(list(map(int, num)))
# map映射
# [1, 2, 3, 4, 5]
print([int(i) for i in num])
# 列表推导式
# [1, 2, 3, 4, 5]

cars = ['bmw', 'audi', 'toyota', 'subaru'] 
print(sorted(cars))  
# ['audi', 'bmw', 'subaru', 'toyota']
print(cars)          
# ['bmw', 'audi', 'toyota', 'subaru']

a = [1,2,3]
b = [4,5,6]
c = [4,5,6,7,8]
zipped = zip(a,b)   
# 返回一个对象<zip object at 0x000001D2A6F817C0>

print(list(zipped))  # list() 转换为列表
# [(1, 4), (2, 5), (3, 6)]

print(list(zip(a,c)))        # 元素个数与最短的列表一致
# [(1, 4), (2, 5), (3, 6)]

a1, a2 = zip(*zip(a,b))      # 与 zip 相反，zip(*) 可理解为解压，返回二维矩阵式

print(list(a1))
# [1, 2, 3]

print(list(a2))
# [4, 5, 6]

pitchers = [('Nolan', 'Ryan'), ('Roger', 'Clemens'),('Schilling', 'Curt')]
first_names, last_names = zip(*pitchers)
print(first_names)
# ('Nolan', 'Roger', 'Schilling')
print(last_names)
# ('Ryan', 'Clemens', 'Curt')

for i, (a, b) in enumerate(zip(seq1, seq2)):
  print('{0}: {1}, {2}'.format(i, a, b))
# 0: foo, one
# 1: bar, two
# 2: baz, three

print(list(reversed(range(10))))
# [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

class A(object):
	bar = 1
a = A()
print(getattr(a, 'bar'))          # 获取属性 bar 值
## 1
print(setattr(a, 'bar', 5))       # 设置属性 bar 值
print(a.bar)
## 5

class Coordinate:    
	x = 10    
	y = -5    
	z = 0  
point1 = Coordinate()  
print(hasattr(point1, 'x')) 
# True
print(hasattr(point1, 'y')) 
# True
print(hasattr(point1, 'z')) 
# True
print(hasattr(point1, 'no'))  # 没有该属性
# False

class A(object): 
	bar = 1 

a = A() 
getattr(a, 'bar')        # 获取属性 bar 值 
# 1
getattr(a, 'bar2')       # 属性 bar2 不存在，触发异常 
# Traceback (most recent call last):  File "<stdin>", line 1, in <module> AttributeError: 'A' object has no attribute 'bar2'
getattr(a, 'bar2', 3)    # 属性 bar2 不存在，但设置了默认值 3
# 3

if condition:
    value = true-expr
else:
    value = false-expr

sex = 1
label = '男' if sex == 1 else '女'
print(label)
# 男

x = 5
print('Non-negative' if x >= 0 else 'Negative')
# Non-negative

with open('workfile', encoding="utf-8") as f:
    read_data = f.read()

# We can check that the file has been automatically closed.
f.closed
# True

# 打开文件
fo = open("test.txt", "r+")
print(fo.read())
# This is the entire file.\n
print(fo.read())
# ''

f.readline()
# 'This is the first line of the file.\n'
f.readline()
# 'Second line of the file\n'
f.readline()
# ''

for line in f:
    print(line, end='')
# This is the first line of the file.
# Second line of the file

f.readlines()
# ['This is the first line of the file\n', 'Second line of the file']

for line in f.readlines():
    print(line, end='')
# This is the first line of the file.
# Second line of the file    

r = f.write('This is a test\n')
# 15

f = open('workfile', 'rb+')
f.write(b'0123456789abcdef')
# 16
f.seek(5)    # 移动到文件的第六个字节
# 5
f.read(1)
# b'5'
f.seek(-3, 2)  # 移动到文件倒数第三个字节
# 13
f.read(1)
# b'd'

import numpy as np 
my_array_1 = np.array([1,2,3])  
print(my_array_1)
# [1 2 3]

my_array_2 = np.array([[1,  2],  [3,  4]])  
print(my_array_2)
# [[1  2] 
#  [3  4]]

a = np.array([[11, 12, 13, 14, 15],
              [16, 17, 18, 19, 20],
              [21, 22, 23, 24, 25],
              [26, 27, 28 ,29, 30],
              [31, 32, 33, 34, 35]])

print(type(a))    # <class 'numpy.ndarray'>
print(a.dtype)    # int64
print(a.size)     # 25
print(a.shape)    # (5, 5)
print(a.itemsize) # 8
print(a.ndim)     # 2

import numpy as np  
x1 = np.arange(5)   
print (x1)
# [0 1 2 3 4]

x2 = np.arange(10,20,2,dtype='float')
print (x2)
# [10. 12. 14. 16. 18.]

import numpy as np
n = np.empty([4,3],dtype= int )
print(n)

# 数组元素为随机值，因为它们未初始化。
# [[7602259 7471215 7536741]
# [6619219 7733362 6488169]
# [4391013 6357100 7536755]
# [7209033 7274598 4456448]]

import numpy as np  

# 默认为浮点数 
x = np.zeros(5)  
print(x)  
# [0. 0. 0. 0. 0.]

# 设置类型为整数 
y = np.zeros((5,), dtype = int)  
print(y)  
# [0 0 0 0 0]

# 自定义类型,i4即int4 
z = np.zeros((2,2), dtype = [('x', 'i4'), ('y', 'i4')])  
print(z)
# [[(0, 0) (0, 0)]
# [(0, 0) (0, 0)]]

import numpy as np  
# 默认为浮点数 
x = np.ones(5)  
print(x)  
# [1. 1. 1. 1. 1.]

# 自定义类型 
y = np.ones([2,2], dtype = int) 
print(y)
# [[1 1]
#  [1 1]]

import numpy as np  
# 创建一个 3x3 的二维数组 
arr = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])  
# 创建一个与 arr 形状相同的，所有元素都为 0 的数组 
zeros_arr = np.zeros_like(arr) 
print(zeros_arr)
# [[0 0 0]
#  [0 0 0]
#  [0 0 0]]

import numpy as np  
# 创建一个 3x3 的二维数组 
arr = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])  
# 创建一个与 arr 形状相同的，所有元素都为 1 的数组 
ones_arr = np.ones_like(arr) 
print(ones_arr)
#[[1 1 1]
# [1 1 1]
# [1 1 1]]

import numpy as np 
a = np.linspace(1,10,10) 

print(a)
## [ 1.  2.  3.  4.  5.  6.  7.  8.  9. 10.]

import numpy as np
 
a = np.array([[1,2,3],[3,4,5],[4,5,6]])  
print (a[...,1])   # 第2列元素
# [2 4 5]
print (a[1,...])   # 第2行元素
# [3 4 5]
print (a[...,1:])  # 第2列及剩下的所有元素
#[[2 3]
# [4 5]
# [5 6]]

import numpy as np   
my_array = np.array([[1,  2],  [3,  4],  [5,  6]])  
y = my_array[[0,1,2], [0,1,0]]   
print (y)
# [1  4  5]

import numpy as np
 
a = np.array([[1,2,3], 
              [4,5,6],
              [7,8,9]])
b = a[1:3, 1:3]
c = a[1:3,[1,2]]
d = a[...,1:]

print(b)
# [[5 6]
# [8 9]]

print(c)
# [[5 6]
# [8 9]]

print(d)
#[[2 3]
# [5 6]
# [8 9]]

import numpy as np 
 
x = np.array([[  0,  1,  2],[  3,  4,  5],[  6,  7,  8],[  9,  10,  11]])  
print (x[x >  5])
# [ 6  7  8  9 10 11]

import numpy as np
users = np.array(['andy','jim','andy'])
data = np.random.randint(1,11,size=(3,4))
print(users,data,sep='\n')
# ['andy' 'jim' 'andy']
# [[1 2 3 4]
#  [5 7 5 9]
#  [5 5 3 8]]
print(data[users == 'andy'])
# [[1 2 3 4]
#  [5 5 3 8]]

print(data[~(names == 'andy')])
#  [5 7 5 9]