Python Shelve: Storing, Retrieving, Updating, and Deleting Data

Hello coders!! In this article, we will be learning about Python shelve and the various functions that we can do in it. A shelve in Python is a dictionary-like object. It is different from “dbm” databases as the value of shelve can be arbitrary Python objects. So, let us now get straight into our topic.

Different functions available in Python Shelve:

MethodDescription
open()open persistent dictionary object
close()synchronize and close persistent dictionary object.
sync()Write back all entries in the cache given that the shelf was opened with the writeback set to True.
get()returns value associated with key
items()tuples list
keys()list of shelf keys
pop()remove specified key and return the corresponding value.
update()update shelf from another dictionary/iterable
values()list of shelf values

Let us see certain examples to understand these functions in a better way.

Example 1: Create a database and store values in Python shelve:

import shelve
sh = shelve.open("student")
sh['name'] = "Prachee"
sh['age'] = 21
sh['marks'] = 95
sh.close()

The above code will create a database sample.dir in the current working directory and store the key-value data in the form of the hashtable.

Example 2: Access the value corresponding to the given key:

sh=shelve.open('student')
sh['age']
21

This can also be written as:

sh.get('age')
21

The get() method returns the value which is associated with the particular key.

Example 3: List the items:

list(sh.items())
[ ( ' name ' , ' Prachee ') , ( ' age ' , 21 ) , ( ' marks ' , 95 ) ]

The items() method returns the key with the corresponding values as a list of tuples.

Example 4: List the keys:

list(sh.keys())
[ ' name ' , ' age ' , ' marks ' ]

The keys() method returns the keys in the form of a list.

Example 5: List the values:

list(sh.values())
[ ' Prachee ', 21 , 95 ]

The values() method returns shelf values in the form of a list.

Example 6: Delete an item in Python Shelve:

sh.pop('marks')
list(sh.items())
95
[ ( ' name ' , ' Prachee ' ) , ( ' age ', 21 ) ]

The pop() function removes the item having the given key from the shelf and returns its corresponding value.

Example 7: Update Python Shelve:

up = {'roll':66 , 'dept':'IT'}
sh.update(up)
list(sh.items())
[ ( ' name ' , ' Prachee ' ) , ( ' age ' , 21 ) , ( ' roll ', 66 ) ]

Using the update() method we can update the shelve with some dictionary or iterable.

Python shelve vs pickle:

SHELVEPICKLE
It is built on top of pickle. It is used to implement a serialization dictionary where the objects are pickled but associated with a key. It is used to serialize some object as a single byte stream in a file.
import shelve
vals = [1, 2, 3, 4, 5]
with shelve.open('shelfE', 'c') as shelf:
shelf['ints'] = vals
with shelve.open('shelfE', 'r') as shelf:
for key in shelf.keys():
print(repr(key), repr(shelf[key]))
import pickle
vals = [1, 2, 3, 4, 5]
with open('pickleE.p', 'wb') as pfile: pickle.dump(vals, pfile)
with open('pickleE.p', 'rb') as pfile: integers = pickle.load(pfile)

print(integers)
OUTPUT:
‘ints’, [1, 2, 3, 4, 5]
OUTPUT:
[1, 2, 3, 4, 5]

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Conclusion:

With this, we come to an end with this article. I hope that the concept of Python shelves and the various functions that are available for shelf operations was cleared from this article.

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