(八)文件

1.读取文件的操作---open()

"""
使用cmd进入文件目录,输入'python',回车进入交互模式
"""
# 创建一个file对象
>>> file=open('test.txt')
# 这里没用read(),而是用for去遍历
>>> for line in file:
...     print(line)
...
#多余的换行是由于print()引起的.
1.This is the first test line.

2.This is the second test line.

3.This is the third test line.
# 这里如果继续循环,因为已经到了末尾,故什么都没有!
>>> for line in file:
...     print(line,end='')
...
# 重新读取,需重新赋值(由于知识面的缺乏,暂时这么理解)
>>>
>>> file1=open('test.txt')
>>> for line in file1:
...     print(line,end='')
...
# print()的换行消失了.
1.This is the first test line.
2.This is the second test line.
3.This is the third test line.

2.创建文件的基本操作:

# 会出现一个空白的test1.txt文档
>>> file2=open('test1.txt','w')
# 执行到下面这句,文档依然空白,但是返回文档的长度
>>> file2.write('This is just for test2!!!')
25
# 关闭了文件后,文件才正式有内容在里面
>>> file2.close()
# review版,上述相当于以下代码
with open('E:/Bin/Python/test/test4.txt','w') as file:
    file.write('This is a review example!!!')

3.读取文件的状态---os,time模块

>>> import os
>>> file_stat=os.stat("test.txt")
>>> file_stat
os.stat_result(st_mode=33206, st_ino=3096224743817860, st_dev=150876, st_nlink=1
, st_uid=0, st_gid=0, st_size=97, st_atime=1546063630, st_mtime=1546063705, st_c
time=1546063630)
# 看不懂时间格式,使用time模块解析
>>> file_stat.st_ctime
1546063630.975547
>>> import time
>>> time.localtime(file_stat.st_ctime)
time.struct_time(tm_year=2018, tm_mon=12, tm_mday=29, tm_hour=14, tm_min=7, tm_s
ec=10, tm_wday=5, tm_yday=363, tm_isdst=0)

4.read(),readline(),readlines()

>>>file3=open('you.md')
# 输出全部的内容,包含换行符,是字符串对象
>>> file3.read()
'You Raise Me Up\nWhen I am down and, oh my soul, so weary;\nWhen troubles come
and my heart burdened be;\nThen, I am still and wait here in the silence,\nUntil
 you come and sit awhile with me.\nYou raise me up, so I can stand on mountains;
\nYou raise me up, to walk on stormy seas;\nI am strong, when I am on your shoul
ders;\nYou raise me up: To more than I can be.'
>>> file4=open('you.md')
# 逐行输出
>>> file4.readline()
# 逐行输出
'You Raise Me Up\n'
# 逐行输出
>>> file4.readline()
'When I am down and, oh my soul, so weary;\n'
>>> file4.readline()
'When troubles come and my heart burdened be;\n'
>>> file4.readline()
'Then, I am still and wait here in the silence,\n'
>>> file5=open('you.md')
# 全部输出,但是结果是一个list对象
>>> file5.readlines()
['You Raise Me Up\n', 'When I am down and, oh my soul, so weary;\n', 'When troub
les come and my heart burdened be;\n', 'Then, I am still and wait here in the si
lence,\n', 'Until you come and sit awhile with me.\n', 'You raise me up, so I ca
n stand on mountains;\n', 'You raise me up, to walk on stormy seas;\n', 'I am st
rong, when I am on your shoulders;\n', 'You raise me up: To more than I can be.'
]

• 当文件很大的时候,如果还是用上述方法,内存可能会崩...这时还是使用for循环去遍历比较妥当,当然,还有另一种推荐的方法---fileinput模块:

import fileinput
# 创建一个fileinput对象
# 我们之前是创建一个open对象
file=fileinput.input('you.md')
for line in file:
    print(line,end='')
>>>
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.

5.seek---"指针"的跳转

>>> file=open('you.md')
>>> file.readline()
'You Raise Me Up\n'
>>> file.readline()
'When I am down and, oh my soul, so weary;\n'
#跳回起始的文件位置
>>> file.seek(0)
0
>>> file.readline()
'You Raise Me Up\n'
#从0开始算起
>>> file.tell()
17