在 Python 3 中打印到混合输出？

Question

有一些标准方法可以将程序的 putput 打印到像 this 这样的输出文件。有没有办法将print 函数用于不同的输出？我明白循环

with open('out.txt', 'w') as f:
    with redirect_stdout(f):
        print('data')

只有在我们进入with-“循环”后才会打印到 out.txt 文件。我怎样才能使用相同的sn-p来代替

for i in range(isteps):
    # Do something with the program 
    with open('out.txt', 'w') as f:
        with redirect_stdout(f):
            print('data') # Writes in out.txt
            print1('Status') # Writes on the screen

请注意，with 之外的 for 循环是进行一些计算的更大程序的一部分。我想打印文件中的数据但同时监视程序的状态（显示在屏幕上）。

Answer 1

您可以通过多种方式做到这一点。不过警告：劫持标准输出或任何标准描述符绝不是一个好主意。与一般情况一样，您的日志记录/打印应该在写入的位置明确。

这样一来，您就可以劫持标准输出。虽然这又不是最好的方法。

import sys

print('This message will be displayed on the screen.')

original_stdout = sys.stdout # Save a reference to the original standard output

with open('filename.txt', 'w') as f:
    sys.stdout = f # Change the standard output to the file we created.
    print('This message will be written to a file.')
    sys.stdout = original_stdout # Reset the standard output to its original value 

更简洁的方法是使用 print 的file 参数：

import sys

print('This message will be displayed on the screen.')

with open('filename.txt', 'w') as f:
    print('This message will be written to a file.', file=f)

对于带有循环的代码，您可以对代码进行洗牌，以便您可以更长时间地控制描述符，或者完全控制描述符并自行管理。

控制文件：

isteps = 4

f = open('out.txt', 'w')  # since we moved this out of a with we need to manage the discriptor
for i in range(isteps):
    # Do something with the program 
    print('data', file=f) # Writes in out.txt
    print('Status') # Writes on the screen
f.close()

改组代码以便保留描述符：

with open('out.txt', 'w') as f:  # No need to manage since we have the with
    for i in range(isteps):
        # Do something with the program
        print('data', file=f) # Writes in out.txt
        print('Status') # Writes on the screen