Python笔记（基础）

print(1)                               # 1

print('we are going to do something')  # we are going to do something

print("we're going to do something")   # we're going to do something
print("we\'re going to do something")  # we're going to do something


print('apple'+'car')                   #applecar
print('apple'+str(4))                  #apple4

print(1+2)                             # 3
print(int('1')+2)                      # 3
print(float('1.2')+2)                  # 3.2

2、数学

+ - * /

** 2**2=4

% 8%2=0

// 9//3=3

3、自变量

命名规则

apple_egg APPLE_EGG appleEgg

定义

a = 1
b = 2
c = 3

a,b,c = 1,2,3

4、while循环

condition = 1
while condition < 10:
    print(condition)
    condition = condition +1

#相当于while（1）
while True:
    print("I'm True")

注意：while结尾处的“:” 有“:”后光标会调到下行会自动缩进

中断循环

注意下面的程序中要退出需要ctrl+c，否则一直在循环中，没法运行下一个程序

a = True

while a:
    b = input('type something')
    if b=='1':
        a = False
    else:
        pass
    print('still in while')
    
print('finish run')

-------------------------------
type something2
still in while

type something1
still in while
finish run

while True:
    b = input('type something')
    if b=='1':
        break
    else:
        pass
    print('still in while')
    
print('finish run')

---------------------------------
type something2
still in while

type something1
finish run

while True:
    b = input('type something')
    if b=='1':
        continue
    else:
        pass
    print('still in while')
    
print('finish run')

------------------------------

type something2
still in while

type something1

type something2
still in while

type something

5、for循环

example_list=[1,2,3,4,5,6,7,8,9,10]
for i in example_list:
    print(i)
    print("outer of for")
print("outer of for")

for i in range(1,10):
    print(i)

注意：range是1，2，3，4，5，6，7，8，9

小技巧： ctrl+[ 可以将选中部分前的缩进消除，一同对齐，然后在Tab

6、if条件

常用符号 < <= > >= == != 可以连着比较大小

x,y,z = 1,2,3
if x<y<z:
    print('true')

x,y,z = 1,2,1
if x<y>z:
    print('true')

if x>y:
    print('x is greater than y')
else:
    print('x is  less or  equal than y')

if else

if x>1:
    print('x > 1')
elif x<1:
    print('x < 1')
else:
    print('x = 1')

if elif else

先满足先跳出

x = -2
if x>1:
    print('x > 1')
elif x<-1:
    print('x < -1')
elif x<1:
    print('x < 1')
else:
    print('x = 1')
print('finish running') 

---------结果-----------
x < -1
finish running

7、def函数

1、定义

def function():
    print('This is a function')
    a=1+2
    print(a)

2、调用

def function():
    print('This is a function')
    a=1+2
    print(a)

function()

3、参数

def fun(a,b):
    c=a*b
    print('the c is',c)

fun(2,3)

4、默认参数

无默认参数

def sale_car(price,color,brand,is_second_hand):
    print('price',price,
          'color',color,
          'brand',brand,
          'is_second_hand',is_second_hand)

sale_car(100,'red','carmy',True)

---------------------------------------------------
price 100 color red brand carmy is_second_hand True

有默认参数

def sale_car(price,color='red',brand='carmy',is_second_hand=True):
    print('price',price,
          'color',color,
          'brand',brand,
          'is_second_hand',is_second_hand)

sale_car(100)
sale_car(123,color='bule')


-----------------------------------------------------------------

price 100 color red brand carmy is_second_hand True
price 123 color bule brand carmy is_second_hand True

注意情况：输入参数时要注意与默认参数的顺序匹配，这个等具体用的再说。

5、return

def fun():
    a = 10
    print(a)
    return a+100

fun()
print(fun())

---------------------
10
110

8、全局&局部变量

全局变量全部一般大写

#没有将a定义为全局变量
APPLE = 100
a = None

def fun():
   a = 20
   return a+100

print('a past=',a)
print(fun())
print('a now=',a)

----------------------
a past= None
120
a now= None

#将a定义为全局变量 global a(global a = 20会报错)
APPLE = 100
a = None

def fun():
    global a
    a = 20
    return a+100

print('a past=',a)
print(fun())
print('a now=',a)

----------------------
a past= None
120
a now= 20

9、文件读写

text = 'This is my first test.\nThis is next line.\nThis is last line.'

my_file=open('my file1.txt','w')
my_file.write(text)
my_file.close()

append_text = '\nThis is appended line'

my_file=open('my file1.txt','a')
my_file.write(append_text)
my_file.close()

注意：文件打开后要关闭（close），否则文件是空白的

file = open('my file1.txt','r')
content = file.readline()
second_read_time = file.readline()
print(content,second_read_time)

---------------------------------
This is my first test.
 This is next line.

readline是逐行读，readlines是存到list中

file = open('my file1.txt','r')
content = file.readlines()
print(content)

-------------------------------------------------------------------------------------------------------
['This is my first test.\n', 'This is next line.\n', 'This is last line.\n', 'This is appended line']

10、类class

class Calculator:
    name = 'Good calculator'
    price = 18

    def add(self,x,y):
        print(self.name)
        print(x+y)
    def minius(self,x,y):
        print(x-y)
    def times(self,x,y):
        print(x*y)
    def divide(self,x,y):
        print(x/y)

calcul = Calculator()
print(calcul.price)
calcul.add(1,2)
calcul.minius(2,4)
calcul.times(3,2)
calcul.divide(8,2)
------------------------------
18
Good calculator
3
-2
6
4.0

注意：self不要漏

init

注意是 def __init__（）

class Calculator:
    def __init__(self,name,price,height,width,weight):
        self.name = name
        self.price = price
        self.h = height
        self.wi = width
        self.we = weight
        
c = Calculator('Good calculator',12,1,2,3)
print(c.wi)

class Calculator:
    def __init__(self,name,price,height=1,width=2,weight=3):
        self.name = name
        self.price = price
        self.h = height
        self.wi = width
        self.we = weight
        
c = Calculator('Good calculator',12)
print(c.h)
b = Calculator('Good calculator',12,10)
print(b.h)

--------------------------------------
1
10

11、input

a_input = int(input('Please give a number:')) # input()  ---   return a  string  '1'
if a_input == 1:
    print('This is a good one')
elif a_input == 2:
    print('See you next time')
else:
    print('Good luck')

12、元组

a_tuple = (12,3,5,25,6)
another_tuple = 12,3,5,25,6

13、列表

a_list = [12,3,67,7,82]

for content in a_list:
    print(content)

for index in range(len(a_list)):
    print('index=',index,'number in list=',a_list[index])

----------------------------------------------------------
12
3
67
7
82
index= 0 number in list= 12
index= 1 number in list= 3
index= 2 number in list= 67
index= 3 number in list= 7
index= 4 number in list= 82

a = [1,2,3,4,2,3,1,1]

a.append(0)            # [1, 2, 3, 4, 2, 3, 1, 1, 0]

a.insert(0,0)          # [0, 1, 2, 3, 4, 2, 3, 1, 1] 在0位插入0

a.remove(1)            # [2, 3, 4, 2, 3, 1, 1] 去掉第一个出现的1

a.sort()               # [1, 1, 1, 2, 2, 3, 3, 4] 从小到大排序

a.sort(reverse=True)   # [4, 3, 3, 2, 2, 1, 1, 1] 从大到小排序

print(a.index(1))      # 0 第一次出现 1 的位置

print(a.count(1))      # 3 出现1的个数

左闭右开：

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

print(a[0])      # 1
print(a[-1])     # 5
print(a[0:3])    # [1, 2, 3]  左闭右开
print(a[:3])     # [1, 2, 3]
print(a[3:5])    # [4, 2]
print(a[-3:])    # [3, 1, 5]

多维列表

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

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

print(a[1])               # 2
print(multi_dim_a[0][1])  # 2
print(multi_dim_a[0])     # [1,2,3]

14、字典

key：value

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

d1 = {'apple':1,'pear':2,'orange':3}
d2 = {1:'a','c':'b'}

print(d1['apple'],d2[1])    # 1 a


del d1['pear']              
print(d1)                   #删除   {'apple': 1, 'orange': 3} 


d1['b'] = 20
print(d1)                   #添加  {'apple': 1, 'orange': 3, 'b': 20}



def fun():
    return 1+2

d3 = {'apple':[1,2,3],'pear':{1:3,3:'a'},'orange':fun()}   #字典中可含列表、字典、函数

print(d3['apple'][0])   # 1
print(d3['pear'][3])    # a
print(d3['orange'])     # 3

15、import模块

注意time.localtime()中的()

#第一种方式

import time

print(time.localtime())



#第二种方式

import time as t

print(t.localtime())


#第三种

from time import time,localtime

print(localtime())
print(time())


#第四种

from time import *

print(localtime())
print(time())
print(gettime())

自己的模块

被调用模块（m1.py）和程序（python1.py）在同一文件夹下或者把m1.py放到和numpy在一起的文件夹下

#m1.py

def printdata(data):
    print('I am m1')
    print(data)


#python1.py

import m1

m1.printdata('I am python1')

----------------------------
I am m1
I am python1

16、错误处理try

try:
    file = open('eee','r+')    #只读+写入
except Exception as e:
    print('there is no file named as eee')
    response = input('do you want to create a new file')
    if response == 'y':
        file = open('eee','w')
    else:
        pass
else:
    file.write('sss')
file.close()

17、zip & lambda & map

a = [1,2,3]
b = [4,5,6]

print(zip(a,b))         # <zip object at 0x000001905D33A688>

print(list(zip(a,b)))   # [(1, 4), (2, 5), (3, 6)]

for i,j in zip(a,b):    # 0.5 8
    print(i/2,j*2)      # 1.0 10
                        # 1.5 12
    
print(list(zip(a,a,b))) # [(1, 1, 4), (2, 2, 5), (3, 3, 6)]

def fun1(x,y):
    return(x+y)
print(fun1(2,3))

#lambda用于定义简单的方程

fun2 = lambda x,y:x+y

print(fun2(2,3))

18、copy

#第一种copy  a,b指向同一内存空间

a = [1,2,3]
b = a
print( id(a) )       # 1719550582216
print( id(b) )       # 1719550582216

b[0] = 11
print(a)             # [11, 2, 3]
a[1] = 22
print(b)             # [11, 22, 3]
print(id(a)==id(b))

#第二种copy  copy.copy  第一层的东西列表指定到不同的内存空间，第二层指向同一层空间

import copy

a = [1,2,3]

c = copy.copy(a)

print(id(a)==id(c))   # False

c[1] = 0
print(c)              # [11, 0, 3]
print(a)              # [11, 22, 3]

a = [1,2,[3,4]]
d =copy.copy(a)

print(id(a)==id(d))        # False
print(id(a[2])==id(d[2]))  # True

a[0] = 0
a[2][0] = 0

print(d)              # [1, 2, [0, 4]]   第一项没改变，但列表里面的改变了

#第三种copy  copy.deepcopy  完完全全的copy，内存空间不会重复

import copy
a = [1,2,[3,4]]

e = copy.deepcopy(a)

print(id(e[2])==id(a[2]))   # False