{"id":8455,"date":"2023-11-08T18:35:00","date_gmt":"2023-11-08T13:05:00","guid":{"rendered":"https:\/\/python-programs.com\/?p=8455"},"modified":"2023-11-10T12:23:12","modified_gmt":"2023-11-10T06:53:12","slug":"python-data-persistence-shelve-module","status":"publish","type":"post","link":"https:\/\/python-programs.com\/python-data-persistence-shelve-module\/","title":{"rendered":"Python Data Persistence &#8211; shelve Module"},"content":{"rendered":"<h2>Python Data Persistence &#8211; shelve Module<\/h2>\n<p>Serialization and persistence affected by functionality in this module depend on the pickle storage format, although it is meant to deal with a dictionary-like object only and not with other Python objects. The shelve module defines an all-important open( ) function that returns the \u2018shelf object representing the underlying disk file in which the \u2018pickled\u2019 dictionary object is persistently stored.<\/p>\n<p><strong>Example<\/strong><\/p>\n<pre>&gt;&gt;&gt; import shelve\r\n&gt;&gt;&gt; obj =shelve.open('shelvetest1)<\/pre>\n<p>In addition to the filename, the <strong>open( )<\/strong> function has two more optional parameters. One is \u2018flag\u2019 which is by default set to \u2018c\u2019 indicating that the file has read\/write access. Other accepted values for flag parameters are <strong>\u2018w\u2019<\/strong> (write-only), <strong>\u2018r\u2019<\/strong> (read-only), and <strong>\u2018n\u2019<\/strong> (new with reading\/write access). The second optional parameter is <strong>\u2018writeback\u2019<\/strong> whose default value is False. If this parameter is set to True, any modification made to the shelf object will be cached in the memory and will only be written to file on calling sync () or <strong>close ( )<\/strong> methods, which might result in the process becoming slow.<\/p>\n<p>Once a shelf object is declared, you can store key-value pair data to it. However, the shelf object accepts only a string as the key. Value can be any valid Python object.<\/p>\n<p><strong>Example<\/strong><\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">&gt;&gt;&gt; obj ['name'] = 'Virat Kohli'\r\n&gt;&gt;&gt; obj ['age']=29\r\n&gt;&gt;&gt; obj ['teams']=['India', 'IndiaU19', 'RCB', 'Delhi']\r\n&gt;&gt;&gt; obj.close( )<\/pre>\n<p>In the current working directory, a file named \u2018shelveset.dir\u2019 will store the above data. Since the shelf is a dictionary-like object, it can invoke familiar methods of built-in diet class. Using the get () method, one can fetch a value associated with a certain key. Similarly, the update () method can be used to add\/modify k-v pairs in shelf objects.<\/p>\n<p><strong>Example<\/strong><\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">&gt;&gt;&gt; obj.get('name')\r\n'Virat Kohli'\r\n&gt;&gt;&gt; dct = { '100s' :64, '50s' :69}\r\n&gt;&gt;&gt; obj.update(dct)\r\n&gt;&gt;&gt; diet(obj)\r\n{'name': 'Virat Kohli', 'age': 29, 'teams':\r\n['India', 'IndiaU19', 'RCB', 'Delhi'], '100s': 64,' 50s' : 69}<\/pre>\n<p>The shelf object also returns views of keys, values, and items,same as the built-in dictionary object.<\/p>\n<p><strong>Example<\/strong><\/p>\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\">&gt;&gt;&gt; keys=list(obj.keys())\r\n&gt;&gt;&gt; keys\r\n['name', 'age', 'teams', '100s', '50s']\r\n&gt;&gt;&gt; values=list(obj.values() )\r\n&gt;&gt;&gt; values\r\n['Virat Kohli', 29, ['India' , 'IndiaU19' 'RCB', 'Delhi\u2019], 64, 69]\r\n&gt;&gt;&gt; items=list(obj.items())\r\n&gt;&gt;&gt; items\r\n[('name', 'Virat Kohli'), (' age 1, 29), ( teams',\r\n['India', \u2019IndiaU19', 'RCB', 'Delhi']), ' 100s ' , 64), ( ' 50s 1 , 69)]<\/pre>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Python Data Persistence &#8211; shelve Module Serialization and persistence affected by functionality in this module depend on the pickle storage format, although it is meant to deal with a dictionary-like object only and not with other Python objects. The shelve module defines an all-important open( ) function that returns the \u2018shelf object representing the underlying &hellip;<\/p>\n<p class=\"read-more\"> <a class=\"\" href=\"https:\/\/python-programs.com\/python-data-persistence-shelve-module\/\"> <span class=\"screen-reader-text\">Python Data Persistence &#8211; shelve Module<\/span> Read More &raquo;<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true},"categories":[5],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v18.9 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Python Data Persistence - shelve Module - Python Programs<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/python-programs.com\/python-data-persistence-shelve-module\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Python Data Persistence - shelve Module - Python Programs\" \/>\n<meta property=\"og:description\" content=\"Python Data Persistence &#8211; shelve Module Serialization and persistence affected by functionality in this module depend on the pickle storage format, although it is meant to deal with a dictionary-like object only and not with other Python objects. 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