8.2、文件操作二

f = open("yesterday", "r")

# 打印前5行
for i in range(5):
    print(f.readline())
'''
What's the trick? I wish I knew 

爱的诀窍是什么 真希望我能懂

I'm so done with thinking through all the things I could've been 

我受够了总是去想我本能完成的所有

And I know you wonder too
'''
# readlines(),每一行最后都有一个换行
print(f.readlines())
# ["What's the trick? I wish I knew \n", '爱的诀窍是什么 真希望我能懂\n']

# 打印文件
for line in f.readlines():
    print(line)

'''
What's the trick? I wish I knew 

爱的诀窍是什么 真希望我能懂

I'm so done with thinking through all the things I could've been 

我受够了总是去想我本能完成的所有

And I know you wonder too
'''
# 剔除换行
for line in f.readlines():
    print(line.strip())
'''
What's the trick? I wish I knew 
爱的诀窍是什么 真希望我能懂
I'm so done with thinking through all the things I could've been 
我受够了总是去想我本能完成的所有
And I know you wonder too
'''

# 打印前五行,low loop
for index, line in enumerate(f.readlines()):
    if index < 5:
        print(index, line.strip())
'''
0 What's the trick? I wish I knew
1 爱的诀窍是什么 真希望我能懂
2 I'm so done with thinking through all the things I could've been
3 我受够了总是去想我本能完成的所有
4 And I know you wonder too
'''

• f.readlines()只适合读小文件，不适合读大文件

# high bigger mode,一行一行读取，不占内存
for line in f:
    print(line.strip())
'''
What's the trick? I wish I knew 
爱的诀窍是什么 真希望我能懂
I'm so done with thinking through all the things I could've been 
我受够了总是去想我本能完成的所有
And I know you wonder too
'''
# 打印前五行
count = 0
for line in f:
    if count < 5:
        print(count, line.strip())
    count += 1
'''
0 What's the trick? I wish I knew
1 爱的诀窍是什么 真希望我能懂
2 I'm so done with thinking through all the things I could've been
3 我受够了总是去想我本能完成的所有
4 And I know you wonder too
'''

• f.seek()
• f.tell()

# 打印文件指针位置
print(f.tell())
# 0
print(f.readline())
# What's the trick? I wish I knew
print(f.tell())
# 33
f.seek(10)
print(f.readline())
#  trick? I wish I knew 

# 打印文件名
print(f.name)
# yesterday

# 是否是tty文件
print(f.isatty())
# False

# 文件指针是否能移动
print(f.seekable())
# True

# 文件是否可写
print(f.writable())
# False

# 判断文件是否关闭
print(f.closed)
# False

• f.flush()，将缓存中的数据刷新到硬盘

#!/usr/bin/env python
# coding: utf-8
# Author: Yerban
import sys
import time

# 例如刷新进度条
for i in range(10):
    sys.stdout.write("#")
    sys.stdout.flush()
    time.sleep(0.5)

for i in range(10):
    sys.stdout.write("#")
    time.sleep(0.5)

• f.truncate()，截断,如果没有值，会将文件清空；如果有值，会动文件的开头开始，到指定位置截断。

f.seek(140)
# 就算把文件指针移动，截断也还是从文件头开始。
f.truncate(100)
print(f.read())
'''
we'res the trick? I wish I knew 
爱的诀窍是什么 真希望我能懂
I'm so done with thinking
'''

• with语句
  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

• 实现简单的shell sed替换功能

with open("yesterday", "r+") as f,\
        open("yesterday1", "w+") as f_new:
    for i in f:
        if "爱的诀窍" in i:
            i = i.replace("爱的诀窍", "爱的诀窍BBB")
        f_new.write(i)
    f_new.seek(0)
    print(f_new.read())

通过脚本后面传参数修改：python_name.py 爱的诀窍 爱的诀窍AAA

#!/usr/bin/env python
# coding: utf-8
# Author: Yerban
import sys

with open("yesterday", "r+") as f,\
        open("yesterday1", "w+") as f_new:
    find_str = sys.argv[1]
    replace_str = sys.argv[2]
    for i in f:
        if find_str in i:
            i = i.replace(find_str, replace_str)
        f_new.write(i)
    f_new.seek(0)
    print(f_new.read())