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Description:

OutputCatcher 0.0.9

Provides a context manager that catches/suppresses output from
sys.stderr and sys.stdout (StdOutCatcher, StdErrCatcher). Also
provides an easy way to gather both stdout and stderr from processes
while optionally piping stdin to the process as a str or bytes.

API

StdOutCatcher / StdErrCatcher
StdOutCatcher(escaped=False, max_length=0)
This will suppress any output running through sys.stdout or
sys.stderr, and save it in an attribute for possible future use.

Arguments

escaped: If truthy, output is “encoded” using repr(), but
without quotes. Default: False
max_length: If non-zero, final output will not exceed
max_length. Once max_length is reached, further write()
calls will be ignored. Default: 0

Usage
from outputcatcher import StdErrCatcher, StdOutCatcher

# Catching stdout
with StdOutCatcher() as fakeout:
print('This is a test. you shouldn\'t see it right away.')
print('Captured stdout: {}'.format(fakeout.output))

# Catching stderr
with StdErrCatcher() as fakeerr:
print('Testing stderr output.', file=sys.stderr)
print('Captured stderr: {}'.format(fakeerr.output))

ProcessOutput
ProcessOutput(args, stdin_data=None, timeout=None, **popenkwargs)
This runs an external process using subprocess.Popen and gathers
both the stdout and stderr output in an attribute for future
use. stdin data can be piped to the process initially, by providing
the data as a str or bytes during initialization.
After initializing a ProcessOutput object with a command to run, and
optional stdin input data, it can either be used as a context manager or
the run() method must be called.
timeout is passed to self.proc.wait() before returning the
output.
Note: As of Python 3.5,
subprocess.run()
can do much of this through the input argument and the
subprocess.CompletedProcess
return value. Though ProcessOutput does provide a handy method for
iterating over output as it is received (iter_stdout, and
iter_stderr).

Arguments

args: Command arguments, same as subprocess.Popen.
stdin_data: str or bytes to send to command as stdin. Default:
None
timeout: Time to wait for process after collecting data. Default:
None
**popenkwargs: Any extra kwargs for Popen(). stdin,
stdout, and stderr are ignored.

Usage
from outputcatcher import ProcessOutput

# Basic usage:
with ProcessOutput(['ls']) as p:
print(p.stdout.decode())

# Checking for stdout and stderr:
with ProcessOutput(['ls', '/totally_nonexistent_dir']) as p:
if p.stdout:
print('Wow, it really does exist: {}'.format(p.stdout.decode()))
else:
print(p.stderr.decode())

# Without a context manager:
p = ProcessOutput(['ls'])
stdout, stderr = p.run()

# Sending stdin data to a process:
stdin_data = 'Hello cat!'
with ProcessOutput(['cat'], stdin_data=stdin_data) as p:
assert p.stdout.decode() == stdin_data
# cat received the data, and piped it back.
print(p.stdout.decode())

# Iterating over stdout data:
p = ProcessOutput(['ls'])
for line in p.iter_stdout():
print(line)