Summary of basic knowledge about python3 learning

1. Data type

1. Number

• int (integer type)

• long (long integer type)

• float（float）

• ##complex (plural)

2. Boolean value

• True or False

3, String

2, Variable

Variable naming rules:

• Variable name can only be any combination of letters, numbers or underscores

• The first character of the variable name cannot be a number

• The variable name cannot be a keyword (for example: and, or,

  continue , break, in, else, print, etc.)

三, String splicing

1. Use the plus sign (+)

name = "Tom"age = 25print(name + "s age is " + str(age))
#输出：Toms age is 25

2. String formatting

name = = 25( %

ps: In

python, use the + sign to connect strings. Every time a + sign appears, you must re-apply for a space in the memory. How many + signs are there? How much space do you need to apply for? Generally do not use the + sign to connect strings.

4. Lists and Tuples

1. List

• Create a list

str_list = ['Tom','Lucy','Mary']
或者
str_list = list(['Tom','Lucy','Mary'])

• Index (access a value in the list)

str_list[0]

• Append (add elements to the end)

str_list.append('lilei')print(str_list)#输出：['Tom', 'Lucy', 'Mary', 'lilei']

• Insert (add an element at the specified position)

str_list.insert(1,'lilei')print(str_list)#输出：['Tom', 'lilei', 'Lucy', 'Mary']

• Delete (delete the specified element)

str_list.remove('Lucy')print(str_list)#输出：['Tom', 'Mary']

• Slice

str_list = [3,4,5,6,7,8,9]
new_1 = str_list[1:3]    #从索引1开始取，取到索引3
new_2 = str_list[0:6:2]  #从索引0开始取，每两位一取，到第6位为止
new_3 = str_list[-2:]    # 取后面2个数
new_4 = str_list[:3]     # 取前面3个数
new_5 = str_list[::3]    #所有数，每3个取一个

print(new_1,new_2,new_3,new_4,new_5)

#输出：[4, 5] [3, 5, 7] [8, 9] [3, 4, 5] [3, 6, 9]

2. Tuple

• Creating tuples

age = (18,25,33)
或者
age = tuple((18,25,33))

Except that elements cannot be modified, added, or deleted, other operations on tuples and lists are almost the same.

5. Dictionary

Use key-value storage method

• Create dictionary

phone = {
    '张三':'13075632152',
    '李四':'15732015632',    
    '王五':'13420321523',
}

• Get the value of the key in the dictionary

print(phone['张三'])      
#如果key不存在，会报错，key用中括号装print(phone.get('老黄'))  
#如果key不存在，返回None,key用小括号装#输出：13075632152
#     None

• Assignment

phone[] =    
phone[] =

• 删除

phone.pop('张三')   
#第一种方法del phone['李四']   
#第二种方法phone.popitem()    
#随机删除某一个

• 遍历

for key in phone:
    print(key,phone[key])

#输出：
# 王五 13420321523
# 张三 13075632152
# 李四 15732015632

• 多级嵌套

phone = {
    '人事部':{'老张':'13700112233','老李':'13432023152'},
    '财务部':{'小丽':'13230555666','小映':'13723688888'},
    '技术部':{'老罗':'13866666333'}
}

print(phone['人事部']['老李'])

#输出：13432023152

六、if语句

1、if...else

age = 16
if age <18:
    print(&#39;你还未成年呢&#39;)
else:
    print(&#39;你已经成年了&#39;)

2、if...elif....else

score = 85
if score > 0 and score< 60:
    print(&#39;你的成绩不及格&#39;)
elif score >= 60 and score <80:
    print(&#39;你的成绩及格了&#39;)
elif score>=80 and score<90:
    print(&#39;你的成绩良好&#39;)
else:
    print(&#39;你的成绩优秀&#39;)

七、while循环

i=0
num=0
while i<=100:
    num+=i
    i+=1
print(&#39;1-100累加等于%d&#39;%num)

八、for...in循环

num = []
for i in range(10):
    num.append(i)
print(num)

#输出：[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

九、用户交互(input)

name = input('请输入你的名字：')
height = input('请输入你的身高：')
print('%s的身高%s厘米' %(name,height))

十、文件基本操作

打开文件：f = open('文件路径'，'模式') 或者 with open('文件路径','模式') as f:

模式：

• r：以只读方式打开文件

• w：打开一个文件只用于写入。如果该文件已存在则将其覆盖。如果该文件不存在，创建新文件。

• a：打开一个文件用于追加。如果该文件已存在，文件指针将会放在文件的结尾。也就是说，新的内容将会被写入到已有内容之后。如果该文件不存在，创建新文件进行写入。

• w+：打开一个文件用于读写。(文件一打开就清空了，还能读到东西吗？)

• a+：打开一个文件用于读写。

读文件：

read() readlines() readline() 的用法

f = open('d:/test.txt','r')  #以只读方式打开文件

print(f.read())  #read()一次读取文件的全部内容

for line in f.readlines():   #readlines()读取整个文件，并按行存进列表
    print(line.strip('\n'))  #去掉行尾的'\n'

while 1:
    line = f.readline()   #readline()每次只读取一行
    print(line.strip('\n'))
    if not line:
        break

f.close()   #关闭文件

写文件：

f =open('d:/test.txt','a')
f.write('hello,boy!\n')  
f.close()

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