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# This file is part of pipe_base. 

# 

# Developed for the LSST Data Management System. 

# This product includes software developed by the LSST Project 

# (http://www.lsst.org). 

# See the COPYRIGHT file at the top-level directory of this distribution 

# for details of code ownership. 

# 

# This program is free software: you can redistribute it and/or modify 

# it under the terms of the GNU General Public License as published by 

# the Free Software Foundation, either version 3 of the License, or 

# (at your option) any later version. 

# 

# This program is distributed in the hope that it will be useful, 

# but WITHOUT ANY WARRANTY; without even the implied warranty of 

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

# GNU General Public License for more details. 

# 

# You should have received a copy of the GNU General Public License 

# along with this program. If not, see <http://www.gnu.org/licenses/>. 

 

"""Module which defines ConfigOverrides class and related methods. 

""" 

 

__all__ = ["ConfigOverrides"] 

 

import ast 

 

import lsst.pex.exceptions as pexExceptions 

from lsst.utils import doImport 

 

from enum import Enum 

 

OverrideTypes = Enum("OverrideTypes", "Value File Python Instrument") 

 

 

class ConfigOverrides: 

"""Defines a set of overrides to be applied to a task config. 

 

Overrides for task configuration need to be applied by activator when 

creating task instances. This class represents an ordered set of such 

overrides which activator receives from some source (e.g. command line 

or some other configuration). 

 

Methods 

---------- 

addFileOverride(filename) 

Add overrides from a specified file. 

addValueOverride(field, value) 

Add override for a specific field. 

applyTo(config) 

Apply all overrides to a `config` instance. 

 

Notes 

----- 

Serialization support for this class may be needed, will add later if 

necessary. 

""" 

 

def __init__(self): 

self._overrides = [] 

 

def addFileOverride(self, filename): 

"""Add overrides from a specified file. 

 

Parameters 

---------- 

filename : str 

Path to the override file. 

""" 

self._overrides.append((OverrideTypes.File, filename)) 

 

def addValueOverride(self, field, value): 

"""Add override for a specific field. 

 

This method is not very type-safe as it is designed to support 

use cases where input is given as string, e.g. command line 

activators. If `value` has a string type and setting of the field 

fails with `TypeError` the we'll attempt `eval()` the value and 

set the field with that value instead. 

 

Parameters 

---------- 

field : str 

Fully-qualified field name. 

value : 

Value to be given to a filed. 

""" 

self._overrides.append((OverrideTypes.Value, (field, value))) 

 

def addPythonOverride(self, python_snippet: str): 

"""Add Overrides by running a snippit of python code against a config. 

 

Parameters 

---------- 

python_snippet: str 

A string which is valid python code to be executed. This is done with 

config as the only local accessible value. 

""" 

self._overrides.append((OverrideTypes.Python, python_snippet)) 

 

def addInstrumentOverride(self, instrument: str, task_name: str): 

"""Apply any overrides that an instrument has for a task 

 

Parameters 

---------- 

instrument: str 

A string containing the fully qualified name of an instrument from 

which configs should be loaded and applied 

task_name: str 

The _DefaultName of a task associated with a config, used to look 

up overrides from the instrument. 

""" 

instrument_lib = doImport(instrument)() 

self._overrides.append((OverrideTypes.Instrument, (instrument_lib, task_name))) 

 

def applyTo(self, config): 

"""Apply all overrides to a task configuration object. 

 

Parameters 

---------- 

config : `pex.Config` 

 

Raises 

------ 

`Exception` is raised if operations on configuration object fail. 

""" 

for otype, override in self._overrides: 

if otype is OverrideTypes.File: 

config.load(override) 

elif otype is OverrideTypes.Value: 

field, value = override 

field = field.split('.') 

# find object with attribute to set, throws if we name is wrong 

obj = config 

for attr in field[:-1]: 

obj = getattr(obj, attr) 

# If input is a string and field type is not a string then we 

# have to convert string to an expected type. Implementing 

# full string parser is non-trivial so we take a shortcut here 

# and `eval` the string and assign the resulting value to a 

# field. Type erroes can happen during both `eval` and field 

# assignment. 

if isinstance(value, str) and obj._fields[field[-1]].dtype is not str: 

try: 

# use safer ast.literal_eval, it only supports literals 

value = ast.literal_eval(value) 

except Exception: 

# eval failed, wrap exception with more user-friendly message 

raise pexExceptions.RuntimeError(f"Unable to parse `{value}' into a Python object") 

 

# this can throw in case of type mismatch 

setattr(obj, field[-1], value) 

elif otype is OverrideTypes.Python: 

exec(override, None, {"config": config}) 

elif otype is OverrideTypes.Instrument: 

instrument, name = override 

instrument.applyConfigOverrides(name, config)