How to Get Realtime Output from Subprocess.Popen in Python?

Getting Realtime Output Using subprocess

Subprocess is a powerful module in Python used to execute other programs and interact with their input and output. However, users may encounter a scenario where they need to retrieve output from the executed program in real time, without any buffering.

Problem Description

The issue arises when using subprocess.Popen with stdout set as a pipe. The output from the wrapped program appears to be buffered, resulting in chunks of data rather than line-by-line delivery. Setting the bufsize parameter to 1 or 0 does not resolve the issue.

Solution: Iterative Reading from readline()

Despite the aforementioned subprocess behavior, the following code snippet effectively retrieves output in real time:

while True:
  line = p.stdout.readline()
  if not line: break
  ...

Using readline() instead of iterating over p.stdout directly bypasses the buffering issue and allows for real-time output retrieval.

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