python中的sys.stdout重定向解读

def print(self, *args, sep=' ', end='\n', file=None): # known special case of print
    """
    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
    
    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file:  a file-like object (stream); defaults to the current sys.stdout.
    sep:   string inserted between values, default a space.
    end:   string appended after the last value, default a newline.
    flush: whether to forcibly flush the stream.
    """
    pass

print("123", file=open("text1.log", "w"))

print("hello")
sys.stdout.write("hello\n")

# 保存原始sys.stdout进行备份
save_stdout = sys.stdout
# sys.stdout重定向，指向文件对象
sys.stdout = open("test.txt", "w")
# print调用sys.stdout的write方法（此时sys.stdout指向文件对象，实际上调用的就是文件对象的write方法），打印到test.txt文件
print("hello world")
# 恢复，标准输出流
sys.stdout = save_stdout
# print调用sys.stdout的write方法，标准输出流默认打印到控制台
print("hello world again")

import sys
import tkinter
import tkinter.scrolledtext


class RedictStdout:
    def __init__(self, scroll_text):
        # 保存原始sys.stdout进行备份
        self.save_stdout = sys.stdout
        # sys.stdout重定向，指向该对象
        sys.stdout = self
        self.scroll_text = scroll_text

    def write(self, message):
        # message即sys.stdout接收到的输出信息
        self.scroll_text.insert(tkinter.END, message)  # 在多行文本控件最后一行插入message
        # self.scroll_text.update()  # 更新显示的文本
        self.scroll_text.see(tkinter.END)  # 始终显示最后一行，不加这句，当文本溢出控件最后一行时，可能不会自动显示最后一行

    def restore(self):
    	# 恢复标准输出流
        sys.stdout = self.save_stdout


def click():
    print("hello word")


window = tkinter.Tk()
scroll_text = tkinter.scrolledtext.ScrolledText(window, bg="pink")
scroll_text.pack()
button = tkinter.Button(window, text="点击", command=click)
button.pack()

# 实例化对象
rs = RedictStdout(scroll_text)
# print调用sys.stdout的write方法，sys.stdout指向rs对象，实际上print调用rs的write方法
# rs的write方法，实现了scrolltext组件插入sys.stdout收到的message信息，即print要打印的信息
window.mainloop()
# 恢复标准输出流
rs.restore()

# 设置日志等级为DEBUG
logging.basicConfig(level=logging.DEBUG)
logging.error("logging error message")

def basicConfig(**kwargs):
    """
    Do basic configuration for the logging system.

    This function does nothing if the root logger already has handlers
    configured, unless the keyword argument *force* is set to ``True``.
    It is a convenience method intended for use by simple scripts
    to do one-shot configuration of the logging package.

    The default behaviour is to create a StreamHandler which writes to
    sys.stderr, set a formatter using the BASIC_FORMAT format string, and
    add the handler to the root logger.

    A number of optional keyword arguments may be specified, which can alter
    the default behaviour.
    ...

class StreamHandler(Handler):
    """
    A handler class which writes logging records, appropriately formatted,
    to a stream. Note that this class does not close the stream, as
    sys.stdout or sys.stderr may be used.
    """

    terminator = '\n'

    def __init__(self, stream=None):
        """
        Initialize the handler.

        If stream is not specified, sys.stderr is used.
        """
        Handler.__init__(self)
        if stream is None:
            stream = sys.stderr
        self.stream = stream

import logging
import sys
import tkinter
import tkinter.scrolledtext


class RedictStdout:
    def __init__(self, scroll_text):
        # 保存原始sys.stdout/sys.stderr进行备份
        self.save_stdout = sys.stdout
        self.save_stderr = sys.stderr
        # sys.stdout/sys.stderr重定向，指向该对象
        sys.stdout = self
        sys.stderr = self
        self.scroll_text = scroll_text

    def write(self, message):
        # message即sys.stdout/sys.stderr接收到的输出信息
        self.scroll_text.insert(tkinter.END, message)  # 在多行文本控件最后一行插入message
        # self.scroll_text.update()  # 更新显示的文本
        self.scroll_text.see(tkinter.END)  # 始终显示最后一行，不加这句，当文本溢出控件最后一行时，可能不会自动显示最后一行

    def restore(self):
    	# 恢复标准输出流
        sys.stdout = self.save_stdout
        sys.stderr = self.save_stderr


def click():
    print("hello word")
    logging.error("logging error message")


window = tkinter.Tk()
scroll_text = tkinter.scrolledtext.ScrolledText(window, bg="pink")
scroll_text.pack()
button = tkinter.Button(window, text="点击", command=click)
button.pack()

# 实例化对象
rs = RedictStdout(scroll_text)
# print调用sys.stdout的write方法，sys.stdout指向rs对象，实际上print调用rs的write方法
# rs的write方法，实现了scrolltext组件插入sys.stdout收到的message信息，即print要打印的信息

# 设置日志等级为DEBUG
logging.basicConfig(level=logging.DEBUG)
# logging.error调用了sys.stderr的write方法，sys.stderr指向rs对象，实际上logging.error调用rs的write方法
# rs的write方法，实现了scrolltext组件插入sys.stderr收到的message信息，即logging.error要打印的信息

window.mainloop()
# 恢复标准输出流
rs.restore()