python - 如何创建和写入 textiowrapper 和 readlines

Question

所以我尝试创建一个文本 io 包装器，然后我可以使用 readlines() 进行单元测试。这是我的尝试，但是当我运行它时 readlines() 什么也不返回:

output = io.BytesIO()
wrapper =  io.TextIOWrapper(
 output,
 encoding='cp1252',
 line_buffering=True,
 )

wrapper.write('Text1')
wrapper.write('Text2')
wrapper.write('Text3')
wrapper.write('Text4')

for line in wrapper.readlines():
    print(line)

我需要更改什么才能获得此输出:

 Text1
 Text2
 Text3
 Text4

Answer 1

了解 TextIOWrapper class在 io模块文档:

A buffered text stream over a BufferedIOBase binary stream.

编辑:使用seek功能:

seek(offset[, whence])

Change the stream position to the given byte offset. offset is interpreted relative to the position indicated by whence. The default value for whence is SEEK_SET. Values for whence are:

• SEEK_SET or 0 – start of the stream (the default); offset should be zero or positive
• SEEK_CUR or 1 – current stream position; offset may be negative
• SEEK_END or 2 – end of the stream; offset is usually negative

Return the new absolute position.

New in version 3.1: The SEEK_* constants.

New in version 3.3: Some operating systems could support additional values, like os.SEEK_HOLE or os.SEEK_DATA. The valid values for a file could depend on it being open in text or binary mode.

尝试以下注释代码片段:

import io, os
output  = io.BytesIO()
wrapper = io.TextIOWrapper(
 output,
 encoding='cp1252',
 # errors=None,         #  defalut
 # newline=None,        #  defalut
 line_buffering=True,
 # write_through=False  #  defalut
 )

wrapper.write('Text1\n')
wrapper.write('Text2\n')
wrapper.write('Text3\n')
# wrapper.flush()                #  If line_buffering is True, flush() is implied
                                 ## when a call to write contains a newline character.

wrapper.seek(0,0)                #  start of the stream
for line in wrapper.readlines():
    print(line)

我原来的答案的其余部分:

<罢工>

<罢工>

print(output.getvalue())         # for gebugging purposes

print( wrapper.write('Text4\n')) #  for gebugging purposes

# for line in wrapper.read():
for line in output.getvalue().decode('cp1252').split(os.linesep):
    print(line)

输出:

==> D:\test\Python\q44702487.py
b'Text1\r\nText2\r\nText3\r\n'
6
Text1
Text2
Text3
Text4

==>

<罢工>