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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/>. 

 

"""Support for reading and writing files to a POSIX file system.""" 

 

__all__ = ("FileFormatter",) 

 

import copy 

from abc import abstractmethod 

 

from lsst.daf.butler import Formatter 

 

 

class FileFormatter(Formatter): 

"""Interface for reading and writing files on a POSIX file system. 

""" 

 

extension = None 

"""Default file extension to use for writing files. None means that no 

modifications will be made to the supplied file extension.""" 

 

@abstractmethod 

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

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

 

Parameters 

---------- 

path : `str` 

Path to use to open the file. 

pytype : `class`, optional 

Class to use to read the file. 

 

Returns 

------- 

data : `object` 

Data read from file. Returns `None` if the file can not be 

found at the given path. 

 

Raises 

------ 

Exception 

Some problem reading the file. 

""" 

pass 

 

@abstractmethod 

def _writeFile(self, inMemoryDataset, fileDescriptor): 

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

 

Parameters 

---------- 

inMemoryDataset : `object` 

Object to serialize. 

fileDescriptor : `FileDescriptor` 

Details of the file to be written. 

 

Raises 

------ 

Exception 

The file could not be written. 

""" 

pass 

 

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

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

 

Usually a no-op. 

 

Parameters 

---------- 

inMemoryDataset : `object` 

Object to coerce to expected type. 

storageClass : `StorageClass` 

StorageClass associated with ``inMemoryDataset``. 

pytype : `class`, optional 

Override type to use for conversion. 

 

Returns 

------- 

inMemoryDataset : `object` 

Object of expected type `pytype`. 

""" 

return inMemoryDataset 

 

def read(self, fileDescriptor, component=None): 

"""Read data from a file. 

 

Parameters 

---------- 

fileDescriptor : `FileDescriptor` 

Identifies the file to read, type to read it into and parameters 

to be used for reading. 

component : `str`, optional 

Component to read from the file. Only used if the `StorageClass` 

for reading differed from the `StorageClass` used to write the 

file. 

 

Returns 

------- 

inMemoryDataset : `object` 

The requested data as a Python object. The type of object 

is controlled by the specific formatter. 

 

Raises 

------ 

ValueError 

Component requested but this file does not seem to be a concrete 

composite. 

""" 

 

# Read the file naively 

path = fileDescriptor.location.path 

data = self._readFile(path, fileDescriptor.storageClass.pytype) 

 

# if read and write storage classes differ, more work is required 

readStorageClass = fileDescriptor.readStorageClass 

if readStorageClass != fileDescriptor.storageClass: 

136 ↛ 137line 136 didn't jump to line 137, because the condition on line 136 was never true if component is None: 

raise ValueError("Storage class inconsistency ({} vs {}) but no" 

" component requested".format(readStorageClass.name, 

fileDescriptor.storageClass.name)) 

 

# Concrete composite written as a single file (we hope) 

try: 

data = fileDescriptor.storageClass.assembler().getComponent(data, component) 

except AttributeError: 

# Defer the complaint 

data = None 

 

# Coerce to the requested type (not necessarily the type that was 

# written) 

data = self._coerceType(data, fileDescriptor.readStorageClass, 

pytype=fileDescriptor.readStorageClass.pytype) 

 

153 ↛ 154line 153 didn't jump to line 154, because the condition on line 153 was never true if data is None: 

raise ValueError("Unable to read data with URI {}".format(fileDescriptor.location.uri)) 

 

return data 

 

def write(self, inMemoryDataset, fileDescriptor): 

"""Write a Python object to a file. 

 

Parameters 

---------- 

inMemoryDataset : `object` 

The Python object to store. 

fileDescriptor : `FileDescriptor` 

Identifies the file to read, type to read it into and parameters 

to be used for reading. 

 

Returns 

------- 

path : `str` 

The `URI` where the primary file is stored. 

""" 

# Update the location with the formatter-preferred file extension 

fileDescriptor.location.updateExtension(self.extension) 

 

self._writeFile(inMemoryDataset, fileDescriptor) 

 

return fileDescriptor.location.pathInStore 

 

def predictPath(self, location): 

"""Return the path that would be returned by write, without actually 

writing. 

 

location : `Location` 

The location to simulate writing to. 

""" 

location = copy.deepcopy(location) 

location.updateExtension(self.extension) 

return location.pathInStore