50 lines
1.8 KiB
Markdown
50 lines
1.8 KiB
Markdown
### subprocess.Popen
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```python
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import subprocess
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process = subprocess.Popen(['echo', 'More output'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
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stdout, stderr = process.communicate()
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stdout, stderr
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```
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Input arguments is a list.
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Notice `communicate()` will **block** until process was finished.
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And the output string `stdout` and `stderr` is of type `byte`. You can convert the output to `string` by:
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```python
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new_string = stdout.decode('utf-8')
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```
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or use `universal_newlines=True` in `subprocess.Popen()`. Example:
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```python
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process = subprocess.Popen(['ping', '-c 4', 'python.org'],
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stdout=subprocess.PIPE,
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universal_newlines=True)
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```
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The `.poll()` will return the exit code of process. If process is still running. `.poll()` will return `None`. Example:
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```python
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process = subprocess.Popen(['ping', '-c 4', 'python.org'], stdout=subprocess.PIPE, universal_newlines=True)
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while True:
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output = process.stdout.readline()
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print(output.strip())
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# Do something else
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return_code = process.poll()
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if return_code is not None:
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print('RETURN CODE', return_code)
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# Process has finished, read rest of the output
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for output in process.stdout.readlines():
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print(output.strip())
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break
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```
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-----
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參考：
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- [docs.python.org: `subprocess.Popen`](https://docs.python.org/3/library/subprocess.html#subprocess.Popen)
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### subprocess.run
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`subprocess.run()`跟`subprocess.Popen()`是一樣的行為，差別是`subprocess.run()`會在process執行完畢之後才return，也就是說流程會被block住。
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`subprocess.run()`會回傳一個型別是`subprocess.CompletedProcess`的object.
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-----
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參考：
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- [docs.python.org: _class_ `subprocess.CompletedProcess`](https://docs.python.org/3/library/subprocess.html#subprocess.CompletedProcess)
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