预科班D11

2020.09.21星期一　　预科班D11

学习内容：

一、基本数据类型及内置方法

1、整形int及浮点型float

+ - * / // ** % > < >= <=

2、字符串类型

(1)按索引值（正向取+反向取）：只能取

name = "jack"
print(name[0])  # j
print(name[-1])  # k
name[0] = "A"  # 报错

(2)切片（顾头不顾尾）

msg = "hello world"
print(msg[2:5])  # llo
print(msg[2]+msg[3]+msg[6])  # llw

(3)长度len

msg = "hello world"
print(len(msg))  # 11

(4)成员运算in和not in

msg = "hello world"
print("heo" in msg)  # False
print("hel" not in msg)  # False

(5)移除空白strip

msg = "    hello   "
res = msg.strip()
print(len(res))  # 5

# 练习
inp_usr = input("username>>>:").strip()
inp_pwd = input("password>>>:").strip()
if inp_usr == "jack" and inp_pwd == "123":
    print("登陆成功！")
else:
    print("登陆失败！")

(6)切分spilt

info = "root:x:0:0::/root:/bin/bash"
res = info.spilt(':')
print(res[-2])  # /root

(7)循环

msg = "hello"
for x in msg:
    print(x)
#h
#e
#l
#l
#o

3、列表类型

l = ['a', 1111, 'c']
l[0] = 'A'
print(l)  # A 1111 c

(1)按索引存取值（正向存取+反向存取）：既可存也可取

l = ['a', 1111, 'c']
l[3] = 666
print(l)  # a 1111 c 666

(2)切片（顾头不顾尾，步长）

l = [111, 222, 333, 444, 555]
print(l[0:3])  # 111 222 333

(3)长度

l = ['a', 1111, 'c']
print(len(l))  # 3

(4)成员运算in和not in

l = ['a', 1111, 'c']
print('c' in l)  # True
print(1111 in l)  # True

(5)追加

l = ['a', 1111, 'c']
l.append('d')
l.append('d')
print(l)  # a 1111 c d d

l = ['a', 1111, 'c']
l.insert(1,6666)
print(l)  # a 6666 111 c

(6)删除

l = [111, 222, 333, 444, 555]
del l(2)
print(l)  # 111 222 444 555

(7)循环

l = [111, 222, 333, 444, 555]
for x in l:
    print(x)

4、字典型dict

(1)按key存取值：可存可取

dic={"k1":111, "k2":2222}
dic["k1"] = 666
print(dic)  # {"k1":666, "k2":2222}

dic={"k1":111, "k2":2222}
dic["k3"] = 7777
print(dic)  # {"k1":111, "k2":2222, "k3":7777}

(2)长度

dic={"k1":111, "k2":2222}
print(len(dic))  # 2

(3)成员运算in和not in

dic={"k1":111, "k2":2222}
print("k1" in dic)  # True
print(2222 in dic)  # False

(4)删除

dic={"k1": 111, "k2": 2222}
del dic["k1"]
print(dic)  # {"k2": 2222}

(5)循环

dic={"k1":111, "k2":2222}
for x in dic:
    print(x, dic(x))

二、文件处理

文本编辑

name = input("请输入你的用户名：")
f = open("user.txt", mode='w')
# print(f)
f.write(name)
f.close()

f = open("user.txt", mode='w')
# print(f)
f.write("hello")
f.close()
f.write("world")  # world报错，因为文件已关闭

文本查看

f = open("user.txt",mode='r')
data = f.read()
print(data)
f.close()  # 一次性读取，对内存要求高，速度快

f = open("user.txt",mode='r')
for line in f:
    print(line,end="")
f.close()  # 按行读取，对硬盘要求高，速度略慢

文件的修改

f = open("user.txt", mode='r+')
f.seek(6)
f.write("wo")
f.close()  # 你好hello 改为 你好wollo

#先以读的形式将user.txt全部读入内存，在内存中修改文件内容且保存在内存中
f = open("user.txt",mode='r', encoding='utf-8')
data = f.read()
res = data.replace("你好","666")
print(res)
f.close()
#以写的形式打开文件，将文件中内容清除掉（原文件内存中有备份）
f = open("user.txt", mode='w',encoding='utf-8')
#将新内容覆盖原文件
f.write(res)
f.close()