两天研习Python基础（十） 文件处理

>>> import locale
>>> locale.getpreferredencoding()
'UTF-8'

#!/usr/bin/python3

# 打开文件，逐行读入并打印
filename = 'hello_world.py'
f = open(filename, 'r', encoding='ascii')

print("Contents of " + filename)
print('-' * 30)
for line in f:
    print(line, end='')

f.close()

# 'with'是一种更简单的方式，会自动处理文件关闭
filename = 'while_loop.py'

print("\n\nContents of " + filename)
print('-' * 30)
with open(filename, 'r', encoding='ascii') as f:
    for line in f:
        print(line, end='')

$ ./file_reading.py
Contents of hello_world.py
------------------------------
#!/usr/bin/python3

print("Hello World")


Contents of while_loop.py
------------------------------
#!/usr/bin/python3

# continuously ask user input till it is a positive integer
usr_string = 'not a number'
while not usr_string.isnumeric():
    usr_string = input("Enter a positive integer: ")

#!/usr/bin/python3

with open('xyz.py', 'r', encoding='ascii') as f:
    for line in f:
        print(line, end='')

$ ./file_reading_error.py
Traceback (most recent call last):
  File "./file_reading_error.py", line 3, in <module>
    with open('xyz.py', 'r', encoding='ascii') as f:
FileNotFoundError: [Errno 2] No such file or directory: 'xyz.py'
$ echo $?
1

>>> f = open('hello_world.py', 'r', encoding='ascii')
>>> f
<_io.TextIOWrapper name='hello_world.py' mode='r' encoding='ascii'>
>>> print(f.read())
#!/usr/bin/python3

print("Hello World")

>>> f = open('hello_world.py', 'r', encoding='ascii')
>>> print(f.readline(), end='')
#!/usr/bin/python3
>>> print(f.readline(), end='')

>>> print(f.readline(), end='')
print("Hello World")

>>> f.close()
>>> print(f.readline(), end='')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file.

>>> f = open('hello_world.py', 'r', encoding='ascii')
>>> all_lines = f.readlines()
>>> all_lines
['#!/usr/bin/python3\n', '\n', 'print("Hello World")\n']

>>> f = open('hello_world.py', 'r', encoding='ascii')

>>> f.closed
False

>>> f.close()
>>> f.closed
True

#!/usr/bin/python3

with open('new_file.txt', 'w', encoding='ascii') as f:
    f.write("This is a sample line of text\n")
    f.write("Yet another line\n")

$ ./file_writing.py
$ cat new_file.txt
This is a sample line of text
Yet another line

#!/usr/bin/python3

import fileinput

with fileinput.input(inplace=True) as f:
    for line in f:
        line = line.replace('line of text', 'line')
        print(line, end='')

$ ./inplace_file_editing.py new_file.txt
$ cat new_file.txt
This is a sample line
Yet another line

$ # 要改变当前目录中所有以.txt结尾的文件，使用
$ ./inplace_file_editing.py *.txt

$ # stdin也可以作为输入
$ echo 'a line of text' | ./inplace_file_editing.py
a line

# 在程序内指定文件名
with fileinput.input(inplace=True, files=('file1.txt', 'file2.txt')) as f:

# 要创建一个不修改的文件备份，传入对应的备份参数
with fileinput.input(inplace=True, backup='.bkp') as f: