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# coding=utf-8
"""
Bridges calls made inside of a Python environments to the Cmd2 host app while maintaining a reasonable
degree of isolation between the two
"""
import sys
from contextlib import redirect_stdout, redirect_stderr
from typing import Optional
from .utils import namedtuple_with_defaults, StdSim
class CommandResult(namedtuple_with_defaults('CommandResult', ['stdout', 'stderr', 'stop', 'data'])):
"""Encapsulates the results from a cmd2 app command
Named tuple attributes
----------------------
stdout: str - output captured from stdout while this command is executing
stderr: str - output captured from stderr while this command is executing. None if no error captured.
stop: bool - return value of onecmd_plus_hooks after it runs the given command line.
data - possible data populated by the command.
Any combination of these fields can be used when developing a scripting API for a given command.
By default stdout, stderr, and stop will be captured for you. If there is additional command specific data,
then write that to cmd2's last_result member. That becomes the data member of this tuple.
In some cases, the data member may contain everything needed for a command and storing stdout
and stderr might just be a duplication of data that wastes memory. In that case, the StdSim can
be told not to store output with its pause_storage member. While this member is True, any output
sent to StdSim won't be saved in its buffer.
The code would look like this:
if isinstance(self.stdout, StdSim):
self.stdout.pause_storage = True
if isinstance(sys.stderr, StdSim):
sys.stderr.pause_storage = True
See StdSim class in utils.py for more information
NOTE: Named tuples are immutable. So the contents are there for access, not for modification.
"""
def __bool__(self) -> bool:
"""Returns True if the command succeeded, otherwise False"""
# If data has a __bool__ method, then call it to determine success of command
if self.data is not None and callable(getattr(self.data, '__bool__', None)):
return bool(self.data)
# Otherwise check if stderr was filled out
else:
return not self.stderr
class PyBridge(object):
"""Provides a Python API wrapper for application commands."""
def __init__(self, cmd2_app):
self._cmd2_app = cmd2_app
self.cmd_echo = False
# Tells if any of the commands run via __call__ returned True for stop
self.stop = False
def __dir__(self):
"""Return a custom set of attribute names"""
attributes = []
attributes.insert(0, 'cmd_echo')
return attributes
def __call__(self, command: str, echo: Optional[bool] = None) -> CommandResult:
"""
Provide functionality to call application commands by calling PyBridge
ex: app('help')
:param command: command line being run
:param echo: if True, output will be echoed to stdout/stderr while the command runs
this temporarily overrides the value of self.cmd_echo
"""
if echo is None:
echo = self.cmd_echo
# This will be used to capture _cmd2_app.stdout and sys.stdout
copy_cmd_stdout = StdSim(self._cmd2_app.stdout, echo)
# Pause the storing of stdout until onecmd_plus_hooks enables it
copy_cmd_stdout.pause_storage = True
# This will be used to capture sys.stderr
copy_stderr = StdSim(sys.stderr, echo)
self._cmd2_app.last_result = None
stop = False
try:
self._cmd2_app.stdout = copy_cmd_stdout
with redirect_stdout(copy_cmd_stdout):
with redirect_stderr(copy_stderr):
stop = self._cmd2_app.onecmd_plus_hooks(command, py_bridge_call=True)
finally:
with self._cmd2_app.sigint_protection:
self._cmd2_app.stdout = copy_cmd_stdout.inner_stream
self.stop = stop or self.stop
# Save the output. If stderr is empty, set it to None.
result = CommandResult(stdout=copy_cmd_stdout.getvalue(),
stderr=copy_stderr.getvalue() if copy_stderr.getvalue() else None,
stop=stop,
data=self._cmd2_app.last_result)
return result
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