文件操作

• 读文件

# 一次行读取文件所有内容
f = open("d:/a.txt", mode="r", encoding="utf-8")
c = f.read()
print(c)
f.close()

"""如果文件太大，可以一行一行的读取"""
f = open("d:/a.txt", mode="r", encoding="utf-8")
l = f.readline()  # 读取一行
print(l.strip())
l = f.readline()  # 读取一行
print(l.strip())
f.close()

# 循环读取文件
f = open("d:/a.txt", mode="r", encoding="utf-8")
for l in f:
    print(l.strip())
f.close()

• 写文件

"""
mode = "w" 文件不存在就创建，如果存在就覆盖
"""
f = open("b.txt", mode="w", encoding="utf-8")
f.write("大家好\n")
f.write("我叫\n")
f.write("xxxx\n")
f.close()

lst = ["张三", "李四0", "王五"]
f = open("b.txt", mode="w", encoding="utf-8")
for item in lst:
    f.write(item)
    f.write("\n")
print("over")
f.close()

• 追加

"""追加内容到文件的后面，model="a" append追加"""
f = open("c.txt", mode="a", encoding="utf-8")
lst = ["张三", "李四0", "王五"]
for item in lst:
    f.write(item)
    f.write("\n")
print("over")
f.close()

"""with 关键字来创建文件，在结束后会自动关闭文件"""
with open("c.txt", mode="a", encoding="utf-8") as f:
    f.write("追加的内容")
    f.write("\n")
print("over")

• 案例

"""复制文件，c.txt 复制到 d.txt"""
with open("c.txt", mode="r", encoding="utf-8") as f1,\
    open("d:/d.txt", mode="w", encoding="utf-8") as f2:
    for line in f1:
        f2.write(line)
print("over")

"""读取二进制文件，model = "rb" 读写二进制文件，就不要加编码格式"""
with open("a.png", mode="rb") as f:
    for l in f:
        print(l)

with open("a.png", mode="rb") as f1,\
    open("b.png", mode="wb") as f2:
    for l in f1:
        f2.write(l)
print("over")

"""
修改文本文件:
1. 读取a.txt文件，将修改后的内容写入a_back.txt副本（新的文件）
2. 删除a.txt文件
3. 将 a_back.txt 重新命名为 a.txt    
"""
import os
import time
with open("a.txt", mode="r", encoding="utf-8") as f1,\
    open("a_back.txt", mode="w", encoding="utf-8") as f2:
    for l in f1:
        if l.startswith("张"):
            l = "李"+l[1:]
        f2.write(l)

time.sleep(2)
# 2 删除a.txt
os.remove("a.txt")
time.sleep(2)
# 3.重命名
os.rename("a_back.txt", "a.txt")
time.sleep(2)
print("over")