在Python 3中打印为混合输出

Question

有一些标准方法可以将程序的输出打印到这样的输出文件中。有没有办法将print函数用于不同的输出？我知道环路

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

只有当我们输入with-"；循环"；。我如何使用相同的代码段来代替

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实现这一点。不过警告：劫持stdout或任何标准描述符从来都不是一个好主意。一般来说，你的日志记录/打印应该明确地写在哪里。

这样一来，你就可以劫持stdout。尽管如此，这并不是最好的方法。

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 

一种更干净的方法是使用打印的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，您可以打乱代码，以便更长时间地处理描述符，或者完全控制描述符并自己管理它。

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()

打乱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