hii readers

readers, This is our first part of python shelve module tutorial

series and in this part, We will discuss what is shelve? and what are the usages of python shelve

module?

But First If You Are New Visitor,

For Introduction Part Click Here,

And

Then, Don't Forget To Check Our Index Because their You can find really many interesting stuff.

So, let's start our Tutorial.

shelve_part_1 slides

In [1]:

#
# ==================================================
#          PYTHON SHELVE MODULE TUTORIAL
# ==================================================
# 
# author   : suraj singh bisht
# contact  :  
#            surajsinghbisht054@gmail.com
#            https://www.bitforestinfo.com
#            
# Here, For This Tutorial
#
# I am using
#
# Operating System : Ubuntu 16.04
# Python Version   : python 2.7.12
# Editor           : ipython notebook
#

In [2]:

#
# Importing Modules
#
import shelve   # shelve : for database api 

import pprint   # pprint : for printing objects

In [3]:

#
# db_name = Name Of Database.
#
# You Can Use Any Name What You Want!
#
db_name = "example_database_shelve.db"

In [4]:

#
# Open Database And Create Shelve Object handler.
# Shelve Object handler Is Very Easy To Use.
# because shelve completely works like a 
# dictonery object.
#
db = shelve.open(db_name)

In [5]:

#
# Creating A List Only For Exmaple Purpose
#
storelist = ["Dog",
            "cat",
            "rat",
            "snake",
            "kite"]

In [6]:

#
# Print Example List
#
pprint.pprint(storelist)

['Dog', 'cat', 'rat', 'snake', 'kite']

In [7]:

#
# Create Example Dictonery
#
storedict = {"rat":"cat",
            "cat":"dog",
            "dog":"wolf",
            "wolf":"lion"}

In [8]:

#
# Print Example Dictonery
#
print storedict

{'rat': 'cat', 'wolf': 'lion', 'dog': 'wolf', 'cat': 'dog'}

In [9]:

#
# Storelist In Database.
#
db['store_list'] = storelist

In [10]:

#
# StoreDict In Database
#
db['store_dict'] = storedict

In [11]:

#
# Close Database
#
db.close()

In [12]:

#
# Again, open database for reading data. 
# but at this time, open only for reading
# data. and for read-only, use "r"
# flag.
#
db = shelve.open(db_name,  flag="r")

In [13]:

#
# Read All Items (Key and Value both)
#
recover_data = db.items()

In [14]:

#
# print data
#
print recover_data

[('store_dict', {'rat': 'cat', 'wolf': 'lion', 'dog': 'wolf', 'cat': 'dog'}), ('store_list', ['Dog', 'cat', 'rat', 'snake', 'kite'])]

In [15]:

#
# Print data in for loop
#
for key, value in recover_data:
    print key, " = ", value

store_dict  =  {'rat': 'cat', 'wolf': 'lion', 'dog': 'wolf', 'cat': 'dog'}
store_list  =  ['Dog', 'cat', 'rat', 'snake', 'kite']

In [16]:

#
# Close Database
#
db.close()

In [17]:

#
# Again Open Database Because Now,
# We Will See, usages of writeback option
#
db = shelve.open(db_name)

In [18]:

#
# Print Stored List
#
print db['store_list']

['Dog', 'cat', 'rat', 'snake', 'kite']

In [19]:

#
# Append Value
#
db['store_list'].append("lion")

In [20]:

#
# Check Appended Value
#
print db['store_list']

['Dog', 'cat', 'rat', 'snake', 'kite']

In [21]:

#
# As, You Can See, Value Is Not Updated,
# Because Shelve Do not track small modification
# By Default. Its Mean If You Want Modification,
# Then, You Need to Modify Complete item.
#
# For Example :
#
#    Take Data
#
modify = db['store_list']
#
# Modify Data
#
modify.append("lion")
#
# Print Data
#
print modify
#
# and modify entire item.
#
db['store_list'] = modify
#
# Close database
#
db.close()
#
# But For This Problem
# Their is A solution in shelve.
# and that solution is writeback option.
# for automatically detect changes in item,
# you need to enable writeback options.
#
# Let's See Practical Example.
#
db = shelve.open(db_name, writeback=True)
#

['Dog', 'cat', 'rat', 'snake', 'kite', 'lion']

In [22]:

#
# Print List
#
print db['store_list']
#
# Append New Value
#
db['store_list'].append("Tiger")
#
# Again, Print List
#
print db['store_list']

['Dog', 'cat', 'rat', 'snake', 'kite', 'lion']
['Dog', 'cat', 'rat', 'snake', 'kite', 'lion', 'Tiger']

In [23]:

#
# As You Can See Above Now, Its Working
# Completely Like A Dictonery Object.
#
db.close()

Our Today's tutorial ends here.

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