Python Library Reference
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6.8.1 Popen3 and Popen4 Objects

Instances of the Popen3 and Popen4 classes have the following methods:

poll()

Returns -1 if child process hasn't completed yet, or its return code otherwise.

wait()

Waits for and returns the status code of the child process. The status code encodes both the return code of the process and information about whether it exited using the exit() system call or died due to a signal. Functions to help interpret the status code are defined in the os module; see section 6.1.5 for the W*() family of functions.

The following attributes are also available:

fromchild

A file object that provides output from the child process. For Popen4 instances, this will provide both the standard output and standard error streams.

tochild

A file object that provides input to the child process.

childerr

Where the standard error from the child process goes is capturestderr was true for the constructor, or None. This will always be None for Popen4 instances.

pid

The process ID of the child process.