python基础知识二

一、运算符

1、运算符需要注意的问题：运算符的执行顺序是从前到后的顺序执行。

if 1 == 2 or 2 > 1 and 1 == 1:
    print("正确")
else:
    print("错误")

2、可以在字符串中使用 in

content = "朝鲜的核试验越演越烈，美国会采取什么样的措施呢"
if "" in content:
    print("核试验")
else:
    print("content")

二、python数据类型

1、整数 int

创建

a = 123
a = int(123)

转换

age = "18"
new_age = int(age)

查看变量是什么类型

print(type(a))

2、布尔值

创建

a = True

b = False

转换

bool(0)    #数字转换只有0为False，其他都为True
bool("")   #字符串转换只有空为False，其他都为True

3、字符串

创建

a = "alex"
a = str("alex")

转换

age = "alex"
new_age = str(age)

字符串的拼接

name = "alex"
gender ="女"
new_str = name + gender
print(new_str)

占位符

name = "我叫李杰，性别：%s，我今年%s岁"
new_str = name%()
print(new_str)

移除空白

name = " connie "
new_name = name.strip()
new_name = name.lstrip()
new_name = name.rstrip()
print(new_name)

分割

user_info = "alex sb123 9"
v = user_info.split(" ")
v = user_info.lsplit(" ",1)
v = user_info.rsplit(" ",1)

索引

val = ""
v = val[0]

val = input(">>>")
i = 0
while i < len(val)
    print(val[i])
    i + =1

切片

name = "我叫李杰，性别男，年龄18岁"
print(name[0])        #取第一个字符
print(name[0:2])      #取前三个字符
print(name[5:9])      #取第六到第十个字符
print(name[5:])       #取第六个字符到最后
print(name[5:-2])     #取第六个字符到倒数第三个
print(name[0:10:2])   #2为步长，从第一个字符到第十一个字符每两个取第一个
print(name[-2:])      #从后往前取两位

4、列表

创建

a = ["alex","猫","connie",5678]
a = list(["alex","猫","connie",5678])

in判断

if "al" in a            #"al"不在a里在a[0]
    pass
if "al" in a[0]
    pass

索引

val = a[0]

切片

a = ["alex","猫","connie",5678]
v = a[0:3:2]
print(v)

追加

a = ["alex","猫","connie",5678]
a.append("daisy")
print(a)

插入

a = ["alex","猫","connie",5678]
a.insert(1,"fish")     #在第二个字符前面插入fish字符
print(a)

移除

a = ["alex","猫","connie",5678]
a.remove("alex")         #根据value删除，如有重复的，只能删除第一个
del a[1]                 #根据索引删除
print("")

修改

a = ["alex","猫","connie",5678]
a[3] = "lady"
print("a")

For循环

a = ["alex","猫","connie",5678]
for item in a:
    print(item)
    break          #跳出循环   
    continue       #跳出当前循环继续下次循环

5、字典

创建

v = {
       "name":" connie"
       "password":"123"
       }                       #字典是无序的

索引

v = {
       "name":" connie"
       "password":"123"
       }             
n = v["name"]

增加或修改

v = {
       "name":" connie"
       "password":"123"
       }                  

v["age"] = 19

print(v)

删除

del v[''name"]

print(v)

循环

v = {
       "name":" connie"
       "password":"123"
       }   

for item in v:                  #只输出key值
     print(item)
for item in v.values():         #只输出value值
     print(item)
for key,value in v.items():     #输出key值和value
     print(item)

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python基础知识二

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