The persistence module

Functions

Functions for storing and retrieving archive files using Python pickle format are

Functions for storing and retrieving pickled archive strings are

Functions for storing and retrieving archive files using JSON format are

Functions for storing and retrieving an archive as a JSON-formatted string are

Module contents

class Archive

An Archive helps to store and retrieve uncertain numbers, so that they can be used in later calculations.

A particular Archive object can either be used to prepare a record of uncertain numbers for storage, or to retrieve a stored record.

add(**kwargs)

Add entries to an archive.

Each entry is given a name that identifies it within the archive.

Example

>>> a = pr.Archive()
>>> x = ureal(1,1)
>>> y = ureal(2,1)
>>> z = ureal(20,1)
>>> a.add(x=x,fred=y)

# Entries can also be added using the name as a key
>>> a['z'] = z

Here f is a file stream opened in mode ‘wb’:

>>> pr.dump(f, a)
>>> f.close()
extract(*args)

Extract uncertain numbers by name

Parameters:args – names of uncertain numbers stored in the archive

If just one name is provided, a single uncertain number is returned. Otherwise a sequence of uncertain numbers is returned.

Example

Continuing the example in add(), but in a different Python session, f is now a file stream opened in ‘rb’ mode:

>>> a = pr.load(f)
>>> f.close()

>>> a.extract('fred')
ureal(2.0,1.0,inf)
>>> x, fred = a.extract('x','fred')
>>> x
ureal(1.0,1.0,inf)

# Entries can also be extracted using the name as a key
>>> a['z']
ureal(20.0,1.0,inf)
items()

Return a list of name -to- uncertain-number pairs

iteritems()

Return an iterator of name -to- uncertain-number pairs

iterkeys()

Return an iterator for names

itervalues()

Return an iterator for uncertain numbers

keys()

Return a list of names

values()

Return a list of uncertain numbers

load(file)

Load an archive from a file

Parameters:file – a file object opened in binary mode (with ‘rb’)

Several archives can be extracted from the same file by repeatedly calling this function.

dump(file, ar)

Save an archive in a file

Parameters:
  • file – a file object opened in binary mode (with ‘wb’)
  • ar – an Archive object

Several archives can be saved in the same file by repeated use of this function.

dumps(ar, protocol=4)

Save an archive pickled in a string

Parameters:
  • ar – an Archive object
  • protocol – encoding type

Possible values for protocol are described in the Python documentation for the pickle module.

protocol=0 creates an ASCII string, but note that many (special) linefeed characters are embedded.

loads(s)

Return an archive object from a pickled string

Parameters:s – a string created by dumps()
dump_json(file, ar, **kw)

Save an archive in a file in JSON format

Parameters:
  • file – a file object opened in text mode (with ‘w’)
  • ar – an Archive object

Keyword arguments will be passed to json.dump()

Only one archive can be saved in a file.

New in version 1.3.0.

load_json(file, **kw)

Load an archive from a file

Parameters:file – a file created by dump_json()

Keyword arguments will be passed to json.load()

New in version 1.3.0.

dumps_json(ar, **kw)

Convert an archive to a JSON string

Parameters:ar – an Archive object

Keyword arguments will be passed to json.dumps()

New in version 1.3.0.

loads_json(s, **kw)

Return an archive object by converting a JSON string

Parameters:s – a string created by dumps_json()

Keyword arguments will be passed to json.loads()

New in version 1.3.0.