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# This file is part of daf_butler. 

# 

# 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/>. 

 

__all__ = ("JsonFormatter", ) 

 

import builtins 

import json 

 

from lsst.daf.butler.formatters.fileFormatter import FileFormatter 

 

 

class JsonFormatter(FileFormatter): 

"""Interface for reading and writing Python objects to and from JSON files. 

""" 

extension = ".json" 

 

unsupportedParameters = None 

"""This formatter does not support any parameters (`frozenset`)""" 

 

def _readFile(self, path, pytype=None): 

"""Read a file from the path in JSON format. 

 

Parameters 

---------- 

path : `str` 

Path to use to open JSON format file. 

 

Returns 

------- 

data : `object` 

Either data as Python object read from JSON file, or None 

if the file could not be opened. 

""" 

try: 

with open(path, "r") as fd: 

data = json.load(fd) 

except FileNotFoundError: 

data = None 

 

return data 

 

def _writeFile(self, inMemoryDataset): 

"""Write the in memory dataset to file on disk. 

 

Will look for `_asdict()` method to aid JSON serialization, following 

the approach of the simplejson module. 

 

Parameters 

---------- 

inMemoryDataset : `object` 

Object to serialize. 

 

Raises 

------ 

Exception 

The file could not be written. 

""" 

with open(self.fileDescriptor.location.path, "w") as fd: 

if hasattr(inMemoryDataset, "_asdict"): 

inMemoryDataset = inMemoryDataset._asdict() 

json.dump(inMemoryDataset, fd) 

 

def _coerceType(self, inMemoryDataset, storageClass, pytype=None): 

"""Coerce the supplied inMemoryDataset to type `pytype`. 

 

Parameters 

---------- 

inMemoryDataset : `object` 

Object to coerce to expected type. 

storageClass : `StorageClass` 

StorageClass associated with `inMemoryDataset`. 

pytype : `type`, optional 

Override type to use for conversion. 

 

Returns 

------- 

inMemoryDataset : `object` 

Object of expected type `pytype`. 

""" 

if not hasattr(builtins, pytype.__name__): 

inMemoryDataset = storageClass.assembler().assemble(inMemoryDataset, pytype=pytype) 

return inMemoryDataset