pydoc > shelve

📛 NAME

shelve - Manage shelves of pickled objects.

🚀 Quick Reference

Use CaseCommandDescription
📂 Open a shelfd = shelve.open(filename)Open a persistent dictionary backed by (g)dbm
💾 Open with writebackd = shelve.open(filename, writeback=True)Cache all accessed entries; write back on close()
📦 Store a valued[key] = valueStore an arbitrary picklable object at key
🔍 Retrieve a valuedata = d[key]Returns a copy of the stored object (KeyError if missing)
❌ Delete a keydel d[key]Remove the entry for key (KeyError if missing)
✔️ Check existencekey in dReturn True if key exists
📋 List all keyslist(d.keys())Retrieve all keys (may be slow)
🚪 Close the shelfd.close()Close the persistent dictionary; may flush changes
🔄 Sync cache to diskd.sync()Write back all cached entries and empty the cache
🔒 Context managerwith shelve.open(filename) as d:Automatically closes the shelf

📚 MODULE REFERENCE

https://docs.python.org/3.10/library/shelve.html

The following documentation is automatically generated from the Python source files. It may be incomplete, incorrect or include features that are considered implementation detail and may vary between Python implementations. When in doubt, consult the module reference at the location listed above.

📖 DESCRIPTION

A "shelf" is a persistent, dictionary-like object. The difference with dbm databases is that the values (not the keys!) in a shelf can be essentially arbitrary Python objects — anything that the "pickle" module can handle. This includes most class instances, recursive data types, and objects containing lots of shared sub-objects. The keys are ordinary strings.

To summarize the interface (key is a string, data is an arbitrary object):

import shelve
d = shelve.open(filename) # open, with (g)dbm filename -- no suffix

d[key] = data   # store data at key (overwrites old data if
                # using an existing key)
data = d[key]   # retrieve a COPY of the data at key (raise
                # KeyError if no such key) -- NOTE that this
                # access returns a *copy* of the entry!
del d[key]      # delete data stored at key (raises KeyError
                # if no such key)
flag = key in d # true if the key exists
list = d.keys() # a list of all existing keys (slow!)

d.close()       # close it

Dependent on the implementation, closing a persistent dictionary may or may not be necessary to flush changes to disk.

Normally, d[key] returns a COPY of the entry. This needs care when mutable entries are mutated: for example, if d[key] is a list,

d[key].append(anitem)

does NOT modify the entry d[key] itself, as stored in the persistent mapping — it only modifies the copy, which is then immediately discarded, so that the append has NO effect whatsoever. To append an item to d[key] in a way that will affect the persistent mapping, use:

data = d[key]
data.append(anitem)
d[key] = data

To avoid the problem with mutable entries, you may pass the keyword argument writeback=True in the call to shelve.open. When you use:

d = shelve.open(filename, writeback=True)

then d keeps a cache of all entries you access, and writes them all back to the persistent mapping when you call d.close(). This ensures that such usage as d[key].append(anitem) works as intended.

However, using keyword argument writeback=True may consume vast amount of memory for the cache, and it may make d.close() very slow, if you access many of d's entries after opening it in this way: d has no way to check which of the entries you access are mutable and/or which ones you actually mutate, so it must cache, and write back at close, all of the entries that you access. You can call d.sync() to write back all the entries in the cache, and empty the cache (d.sync() also synchronizes the persistent dictionary on disk, if feasible).

🏛️ CLASSES

collections.abc.MutableMapping(collections.abc.Mapping)

🗄️ class Shelf(collections.abc.MutableMapping)

Base class for shelf implementations.

This is initialized with a dictionary-like object. See the module's __doc__ string for an overview of the interface.

Method resolution order:

🔧 Methods defined here:

📋 Inherited from collections.abc.MutableMapping:

📋 Inherited from collections.abc.Mapping:

🔒 Data descriptors defined here:

__abstractmethods__ = frozenset()

🗄️ class BsdDbShelf(Shelf)

Shelf implementation using the "BSD" db interface.

This adds methods first(), next(), previous(), last() and set_location() that have no counterpart in [g]dbm databases.

The actual database must be opened using one of the "bsddb" modules "open" routines (i.e. bsddb.hashopen, bsddb.btopen or bsddb.rnopen) and passed to the constructor.

Method resolution order:

🔧 Methods defined here:

📋 Inherited from Shelf:

Data descriptors inherited from Shelf: __dict__, __weakref__

__abstractmethods__ = frozenset()

🗄️ class DbfilenameShelf(Shelf)

Shelf implementation using the "dbm" generic dbm interface.

This is initialized with the filename for the dbm database. See the module's __doc__ string for an overview of the interface.

Method resolution order:

🔧 Methods defined here:

📋 Inherited from Shelf:

Data descriptors inherited from Shelf: __dict__, __weakref__

__abstractmethods__ = frozenset()

⚙️ FUNCTIONS

📂 open(filename, flag='c', protocol=None, writeback=False)

Open a persistent dictionary for reading and writing.

The filename parameter is the base filename for the underlying database. As a side-effect, an extension may be added to the filename and more than one file may be created. The optional flag parameter has the same interpretation as the flag parameter of dbm.open(). The optional protocol parameter specifies the version of the pickle protocol.

See the module's __doc__ string for an overview of the interface.

📦 DATA

__all__ = ['Shelf', 'BsdDbShelf', 'DbfilenameShelf', 'open']

📄 FILE

/usr/lib/python3.10/shelve.py

shelve □✕
📛 NAME 🚀 Quick Reference 📚 MODULE REFERENCE 📖 DESCRIPTION 🏛️ CLASSES
🗄️ class Shelf(collections.abc.MutableMapping) 🗄️ class BsdDbShelf(Shelf) 🗄️ class DbfilenameShelf(Shelf)
⚙️ FUNCTIONS
📂 open(filename, flag='c', protocol=None, writeback=False)
📦 DATA 📄 FILE

Generated by phpman v4.9.27 · Markdown · JSON · MCP Author: Che Dong Under GNU General Public License
2026-07-18 13:21 @216.73.216.114
CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)
Valid XHTML 1.0 Transitional!Valid CSS!
Enhanced by LLM: deepseek-v4-flash / taotoken.net / www.chedong.com - original format

^_top_^