[英]How to redirect output with subprocess in Python?
What I do in the command line:我在命令行中执行的操作:
cat file1 file2 file3 > myfile
In Python 3.5+ to redirect the output, just pass an open file handle for the stdout
argument to subprocess.run
:在Python 3.5+中重定向输出,只需将stdout
参数的打开文件句柄传递给subprocess.run
:
# Use a list of args instead of a string
input_files = ['file1', 'file2', 'file3']
my_cmd = ['cat'] + input_files
with open('myfile', "w") as outfile:
subprocess.run(my_cmd, stdout=outfile)
As others have pointed out, the use of an external command like cat
for this purpose is completely extraneous.正如其他人指出的那样,为此目的使用像cat
这样的外部命令是完全无关紧要的。
UPDATE: os.system is discouraged, albeit still available in Python 3.更新:不鼓励使用 os.system,尽管在 Python 3 中仍然可用。
Use os.system
:使用os.system
:
os.system(my_cmd)
If you really want to use subprocess, here's the solution (mostly lifted from the documentation for subprocess):如果您真的想使用子流程,这是解决方案(主要来自子流程的文档):
p = subprocess.Popen(my_cmd, shell=True)
os.waitpid(p.pid, 0)
OTOH, you can avoid system calls entirely: OTOH,您可以完全避免系统调用:
import shutil
with open('myfile', 'w') as outfile:
for infile in ('file1', 'file2', 'file3'):
shutil.copyfileobj(open(infile), outfile)
@PoltoS I want to join some files and then process the resulting file. @PoltoS 我想加入一些文件,然后处理生成的文件。 I thought using cat was the easiest alternative.我认为使用 cat 是最简单的选择。 Is there a better/pythonic way to do it?有没有更好的/pythonic方法来做到这一点?
Of course:当然:
with open('myfile', 'w') as outfile:
for infilename in ['file1', 'file2', 'file3']:
with open(infilename) as infile:
outfile.write(infile.read())
One interesting case would be to update a file by appending similar file to it.一个有趣的案例是通过向文件附加类似文件来更新文件。 Then one would not have to create a new file in the process.这样就不必在此过程中创建新文件了。 It is particularly useful in the case where a large file need to be appended.它在需要附加大文件的情况下特别有用。 Here is one possibility using teminal command line directly from python.这是直接从 python 使用终端命令行的一种可能性。
import subprocess32 as sub
with open("A.csv","a") as f:
f.flush()
sub.Popen(["cat","temp.csv"],stdout=f)
size = 'ffprobe -v error -show_entries format=size -of default=noprint_wrappers=1:nokey=1 dump.mp4 > file'
proc = subprocess.Popen(shlex.split(size), shell=True)
time.sleep(1)
proc.terminate() #proc.kill() modify it by a suggestion
size = ""
with open('file', 'r') as infile:
for line in infile.readlines():
size += line.strip()
print(size)
os.remove('file')
When you use subprocess , the process must be killed.This is an example.If you don't kill the process , file will be empty and you can read nothing.It can run on Windows .I can`t make sure that it can run on Unix.当你使用子进程时,进程必须被杀死。这是一个例子。如果你不杀死进程,文件将是空的,你什么也读不到。它可以在Windows上运行。我不能确保它可以在 Unix 上运行。
如果您的args<\/code>看起来像
['sh', '-c', 'cat file1 file2 file3 > myfile']<\/code>它将起作用,这意味着
cat<\/code>的输出不会通过 Python 而是在 shell 中生成(插入
sh -c<\/code>你可以使用
bash -c<\/code> )
"
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.