OutputCatcher 0.0.5

Catches/silences stdout/stderr output.

A context manager that catches/suppresses output from sys.stderr and sys.stdout.

API

StdOutCatcher / StdErrCatcher

StdOutCatcher(escaped=False, max_length=0)

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 not write to the original stream. 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)

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.

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().

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())