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python3 file operation example code

Mar 26, 2017 pm 06:35 PM

This article mainly introduces the operation example code of python3 files in detail, which has certain reference value. Interested friends can refer to it

# Auther: Aaron Fan

'''
打开文件的模式有三种:
r,只读模式(默认)。
w,只写模式。【不可读;不存在则创建;存在则删除内容;因为会清空原有文件的内容,一定要慎用】
a,追加模式。【可读;   不存在则创建;存在则只追加内容;】
注意最后要记得关闭文件:f.close()
python只能将字符串写入到文本文件。要将数值数据存储到文本本件中,必须先试用函数str()将其转换为字符串格式。
#r模式(只读模式)
f = open('yesterday',encoding='utf-8')
data = f.read()
f.close()
print(data)
#只读文件的前5行:
f = open('yesterday','r',encoding='utf-8')
for i in range(5):
   print(f.readline())
#以列表的方式读取这个文件
f = open('yesterday','r',encoding='utf-8')
for line in f.readlines():
   print(line)
#对文件的第3行,做一个特殊的打印(这种方式比较低效,因为它会先把文件全部读取到内存中,文件较大时会很影响性能)
f = open('yesterday','r',encoding='utf-8')
for index,line in enumerate(f.readlines()):
   if index == 2:
       print('-----测试线----',line)
       continue
   print(line)
#比较高效的,逐行读取文件内容,因为它是一行一行的去读取文件,不会先把文件一次性全部读取到内存中
f = open('yesterday','r',encoding='utf-8')
for line in f:
   print(line)
#比较高效的,对文件的3三行进行过特殊打印
f = open('yesterday','r',encoding='utf-8')
count = 0
for line in f:
   if count == 2:
       print('------测试线----:',line)
   count += 1
   print(line)

#w模式(如果没有就创建文件,如果有就清空文件,一定要慎用)
f = open('yesterday','w',encoding='utf-8')
f.write("这就是一行测试\n")
f.write("测试2\n")
f.write("测试3")

#a模式(追加模式,如果没有就创建文件,如果有就把内容追加进去)
f = open('yesterday','a',encoding='utf-8')
f.write("test1\n")

#文件光标的操作
f = open('yesterday','r',encoding='utf-8')
#获得文件的光标
print(f.tell())
print(f.readline())
print(f.tell())
#回到最开始的位置(也可以指定一个位置,前提是你得知道你去往的字符具体在哪个位置才行)
f.seek(0)

#显示文件的编码
print(f.encoding)
#显示文件句柄的编号(我并不确定这个说法是否正确,用到时请仔细去查一下)
print(f.fileno())
#测试是否是一个终端设备文件
print(f.isatty())
#把缓存的内容刷新到硬盘(进度条那个脚本里有写一个示例)
f.flush()
#指定文件从哪里开始截断,如果没有参数,默认从0开始等于清空了这个文件
#f.truncate()

#r+ 模式(读,追加模式)
f = open('yesterday','r+',encoding='utf-8')
data = f.read()
print(data)
f.write("test...\n")

#还有 w+写读模式, a+追加读模式,这一般不用,真用到了再去了解下吧
#rb 模式,以二进制的方式读取这个文件
#wb 模式,二进制写
'''

'''
#with语句(很实用,记得要经常用哟~,在《Python编程从入门到实战》那本书里的文件与异常那一章有详细用法)
#为了避免打开文件后忘记关闭,可以通过管理上下文,即:
with open('log','r') as f:

   ...
#如此方式,当with代码块执行完毕时,内部会自动关闭并释放文件资源。
#在Python 2.7 后,with又支持同时对多个文件的上下文进行管理,即:
with open('log1') as obj1, open('log2') as obj2:
   pass
'''
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