如何创建和写入 textiowrapper 和 readlines

Question

所以我正在尝试创建一个文本 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() returns 什么都没有：

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

阅读 io 模块文档中的 TextIOWrapper class：

A buffered text stream over a BufferedIOBase binary stream.

编辑：使用seek函数：

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.

尝试以下评论代码段：

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：

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 ==>

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