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文件操作w+和r+和b模式。
一般（如python，c）等的文件操作里面，
+表示可读可写，那么r+模式和w+模式有什么区别吗？
还有b好像是表示二进制模式打开，文本模式和二进制模式有什么区别吗？如果一个txt(文本文件）用二进制打开，会有问题吗？如果没有问题，那么用二进制打开后，有什么特别之处吗？
windows下notepad下编辑文件时，算得上是文本模式吧？什么时候我们编辑的文件是二进制的？貌似在windows系统下，我们很少用到二进制文件啊？
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w会把原来的文件清空吧。
txt文件用二进制打开没有问题，但是读的时候会多出一个回车符（\r\n），写的时候也少写一个回车符。你自己试试就知道了。
当你需要读写dll, mp3，png之类的文件时，就需要二进制模式。否则\r会被忽略和混淆。
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r+：可读可写，若文件不存在，报错
w+: 可读可写，若文件不存在，创建
文本模式：遇换行符时根据操作系统不同自动转换换行符，比如读文件时遇\n在windows下转换成\n\r。
二进制模式：遇换行符时原样写入和原样读出，不进行转换
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>>> help(open)
Help on built-in function open in module io:
open(...)
open(file, mode='r', buffering=-1, encoding=None,
errors=None, newline=None, closefd=True) -> file object
Open file and return a stream. Raise IOError upon failure.
file is either a text or byte string giving the name (and the path
if the file isn't in the current working directory) of the file to
be opened or an integer file descriptor of the file to be
wrapped. (If a file descriptor is given, it is closed when the
returned I/O object is closed, unless closefd is set to False.)
mode is an optional string that specifies the mode in which the file
is opened. It defaults to 'r' which means open for reading in text
mode. Other common values are 'w' for writing (truncating the file if
it already exists), and 'a' for appending (which on some Unix systems,
means that all writes append to the end of the file regardless of the
current seek position). In text mode, if encoding is not specified the
encoding used is platform dependent. (For reading and writing raw
bytes use binary mode and leave encoding unspecified.) The available
modes are:
========= ===============================================================
Character Meaning
--------- ---------------------------
'r' open for reading (default)
'w' open for writing, truncating the file first
'a' open for writing, appending to the end of the file if it exists
'b' binary mode
't' text mode (default)
'+' open a disk file for updating (reading and writing)
'U' universal newline mode (for backwards compatibility; unneeded
for new code) ========= ===============================================================
The default mode is 'rt' (open for reading text). For binary random
access, the mode 'w+b' opens and truncates the file to 0 bytes, while
'r+b' opens the file without truncation.
Python distinguishes between files opened in binary and text modes,
even when the underlying operating system doesn't. Files opened in
binary mode (appending 'b' to the mode argument) return contents as
bytes objects without any decoding. In text mode (the default, or when
't' is appended to the mode argument), the contents of the file are
returned as strings, the bytes having been first decoded using a
platform-dependent encoding or using the specified encoding if given.
buffering is an optional integer used to set the buffering policy.