【python学习笔记】文件的创建、读取和写入
本博客参考了如何使用python打开及读写文件（基础篇）
文件创建
创建空文件
os.mknod("test.txt")
该方法不适用于Windows系统
直接打开一个文件，如果文件不存在则创建文件
import os
file = open("test01.txt",'w')
file.close()
with open("test01.txt", 'w', encoding="utf-8") as f:
f.write("test")
with open("test01.txt", 'r', encoding="utf-8") as f:
print(f.read())
test
#封装的文件创建方法
def text_create(name):
#此处是文件保存位置，默认为项目根目录
savepath = ""
filename = savepath + name + '.txt'
filename = name + '.txt'
file = open(filename, 'w')
file.close()
text_create('test')
文件写入
这里的写入我指的不只是write操作
write
write操作只能把文件的内容全部清空后重写写入
with open("test.txt", 'w', encoding="utf-8") as f:
f.write("the 1st line\n")
#读取操作
with open("test.txt", 'r', encoding="utf-8") as f:
print(f.read())
print("-------------------")
with open("test.txt", 'w', encoding="utf-8") as f:
f.write("the 2nd line\n")
with open("test.txt", 'r', encoding="utf-8") as f:
print(f.read())
the 1st line
-------------------
the 2nd line
append
append操作是在原有基础上追加内容
with open("test.txt", 'a', encoding="utf-8") as f:
f.write("the 3rd line\n")
#读取操作
with open("test.txt", 'r', encoding="utf-8") as f:
print(f.read())
the 2nd line
the 3rd line
删除内容
with open("test01.txt", 'r', encoding="utf-8") as f:
print(f.read())
#f.truncate(n)从头开始，第n个字符后截断并清除
#即显示前n个字符
with open("test01.txt", 'a', encoding="utf-8") as f:
f.truncate(2)
with open("test01.txt", 'r', encoding="utf-8") as f:
print(f.read())
print("-------------")
#清除文件内容
with open("test01.txt", 'w', encoding="utf-8") as f:
f.truncate()
with open("test01.txt", 'r', encoding="utf-8") as f:
print(f.read())
test
te
-------------
#删除文件
os.remove("test01.txt")
#检验文件是否存在
os.path.exists("test01.txt")
False
文件读取
open()+close()
#打开文件
f = open('test.txt','r',encoding = 'utf-8')
#再使用read()方法，查看文件里的内容：
print(f.read())
#关闭文件
f.close()
the 2nd line
the 3rd line
注意
- 当未指定文件编码格式时，如果文件编码格式与当前默认的编码格式不一致，那么文件内容的读写将出现错误，在python3下，可以通过encoding参数指定编码方式。
- 结尾一定要使用close（）来关闭文件。
- 当读写文件本身有错误时，即使使用close（）也可能会出现文件无法正常关闭的现象。
with open（）
with 的作用相当于调用close（）方法，文件会自动关闭，这种方法的安全系数更高，同时也避免了有些时候忘记关闭文件的毛病。
with open('test.txt','r',encoding = 'utf-8') as f:
print(f.read())
the 2nd line
the 3rd line
with open('test.txt','a',encoding = 'utf-8') as f:
f.write("test\ntest2\ntest3\n")
with open('test.txt','r',encoding = 'utf-8') as f:
print(f.read())
the 2nd line
the 3rd line
test
test2
test3
几种读取的方式
#读取全部
with open('test.txt','r',encoding = 'utf-8') as f:
print(f.read())
print(f.tell()) #打印指针位置，read()操作之后指针在末尾
f.seek(0) #移动指针（0-文件头，默认值；1-当前位置；2-文件尾）
print(f.tell())
print("-----------")
#读取第一行
with open('test.txt','r',encoding = 'utf-8') as f:
print(f.readline())
print("-----------")
#读取前n个字符,这里n=2
with open('test.txt','r',encoding = 'utf-8') as f:
print(f.readline(2))
print("-----------")
#一次读取所有内容并按行返回list
with open('test.txt','r',encoding = 'utf-8') as f:
print(f.readlines())
print("-----------")
the 2nd line
the 3rd line
test
test2
test3
48
0
-----------
the 2nd line
-----------
th
-----------
['the 2nd line\n', 'the 3rd line\n', 'test\n', 'test2\n', 'test3\n']
-----------
