Python3 写入文件

Demo:

file = open("test.txt", "wb")
file.write("string")

上面这段代码运行会报类型错误：TypeError: a bytes-like object is required, not \'str\' 

wirte方法是将一个字节缓冲区写入到目标文件中，而不支持string类型

write源码：

def write(self, *args, **kwargs): # real signature unknown
    """
    Write buffer b to file, return number of bytes written.

    Only makes one system call, so not all of the data may be written.
    The number of bytes actually written is returned.  In non-blocking mode,
    returns None if the write would block.
    """
    pass

注：python3 将字符串写入到目标文件时，必须先将字符串转换为字节才能写入，python2可以直接将字符串写入到目标文件中