{"id":181,"date":"2019-02-05T06:25:15","date_gmt":"2019-02-05T06:25:15","guid":{"rendered":"https:\/\/www.kindsonthegenius.com\/python\/?p=181"},"modified":"2019-03-02T03:54:07","modified_gmt":"2019-03-02T03:54:07","slug":"12-python-dictionary","status":"publish","type":"post","link":"https:\/\/www.kindsonthegenius.com\/python\/12-python-dictionary\/","title":{"rendered":"Python – Dictionary"},"content":{"rendered":"

In this lesson you will learn how to use Python Dictionary. We would cover the following topics.<\/p>\n

    \n
  1. \n
      \n
    1. Introduction to Python Dictionary<\/a><\/li>\n
    2. Creating a Dictionary<\/a><\/li>\n
    3. Accessing Values in a Dictionary<\/a><\/li>\n
    4. Modifying a Dictionary<\/a><\/li>\n
    5. Dictionary Functions in Python<\/a><\/li>\n
    6. Dictionary Methods in Python<\/a><\/li>\n
    7. Watch the Video<\/a><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n

       <\/p>\n

      1. Introduction to Python Dictionary<\/strong><\/h4>\n

      A dictionary is Python store items the way a normal dictionary stores item. In each entry, you have two things: a key and a value. That is why we say, dictionary stores key-value pairs. The key and its value is separated using color (:). Then each entry is separate from the other by a comma. Also a python dictionary is created using curly braces { }.<\/p>\n

      While the keys in a dictionary are unique, the values are not. So key in a dictionary are immutable.<\/p>\n

       <\/p>\n

      2. Creating in a Dictionary<\/strong><\/h4>\n

      Unlike the list and tuples, you create\u00a0 dictionary using curly braces. Then you use comma to separate each key-value pair in the dictionary.<\/p>\n

      student =<\/span> {\r\n    \"name\"<\/span>: \"Emily William\"<\/span>,\r\n    \"Location\"<\/span>: \"Nigeria\"<\/span>,\r\n    \"Score\"<\/span> : 89<\/span>,\r\n    \"Grade\"<\/span> : 'A'<\/span>,\r\n    \"Address\"<\/span> : \"No 21 Bills Street\"<\/span>\r\n}\r\n<\/pre>\n
      The code above creates a dictionary named student. This represents the record of a particular student.<\/p>\n
       <\/p>\n
       <\/p>\n
      3. Accessing Values in Dictionary<\/strong><\/h4>\n
      How can we access values in a dictionary? Unlike lists and tuples that use indexes, dictionary uses key. So you specify the key to access the value. Let’s use a typical example of a dictionary containing the days of the week.<\/p>\n
      This is shown below.<\/p>\n
      daysOfWeek =<\/span> {\r\n    1<\/span> : \"Monday\"<\/span>,\r\n    2<\/span> : \"Tuesday\"<\/span>,\r\n    3<\/span> : \"Wednesday\"<\/span>,\r\n    4<\/span> : \"Thursday\"<\/span>,\r\n    5<\/span> : \"Friday\"<\/span>,\r\n    6<\/span> : \"Saturday\"<\/span>,\r\n    7<\/span> : \"Sunday\"<\/span>  \r\n}\r\n<\/pre>\n
      To access the values (given as strings) we used the keys (given as numbers). So look at the code below. What do you think the output would be?<\/p>\n
      print<\/span>(“Today is “<\/span> +<\/span> daysOfWeek[1<\/span>])
      \nprint<\/span>(“Tomorrow is “<\/span> +<\/span> daysOfWeek[2<\/span>])<\/p>\n
       <\/p>\n
      The output would be:<\/p>\n
      Today is<\/span> Monday\r\nTomorrow is<\/span> Tuesday\r\n<\/pre>\n
      Note that we can only access values using keys that exist in the dictionary. For example we cannot day daysOfWeek(8). This would result in an error because there is not 8 in the dictionary.<\/p>\n
       <\/p>\n
       <\/p>\n
      4. Modifying a Dictionary<\/strong><\/h4>\n
      Remember we cannot modify the keys. We can only modify the values. These we can do in three ways:<\/p>\n
        \n
      • add new entry<\/li>\n
      • update the value of an entry<\/li>\n
      • delete an entry<\/li>\n<\/ul>\n
         <\/p>\n
        Add new entry<\/strong><\/p>\n
        To add a new entry into a dictionary, you use that add method of the dictionary. So\u00a0 to add an entry Nationality and Language to the original dictionary we created, we can say:<\/p>\n
        <\/p>\n
        student[\"Nationality\"<\/span>] =<\/span> \"American\"<\/span>\r\nstudent[\"Language\"<\/span>] =<\/span> \"English\"<\/span>\r\n<\/pre>\n
         <\/p>\n
        Update value of an entry<\/strong><\/p>\n
        To update and entry you simply assign another value to the key of the entry you want to update. The following would update the name and address of the student:<\/p>\n
        student[\"Name\"<\/span>] =<\/span> \"Emily Normal William\"<\/span>\r\nstudent[\"Address\"<\/span>] =<\/span> \"25 Western Avenue 1104 BP\"<\/span>\r\n\r\n\r\n<\/pre>\n
        Delete an entry<\/strong><\/p>\n
        To delete an entry from a dictionary, you use the del keyword. Example is given below:<\/p>\n
        <\/p>\n
        del<\/span> student[\"Location\"<\/span>]\r\n<\/pre>\n
        Note that the above code would delete both the key and the value.<\/p>\n
         <\/p>\n
         <\/p>\n
        5. Dictionary Functions in Python<\/strong><\/h4>\n
        Python provides a number of useful functions you can use with dictionaries. These functions are given in the table below. I recommend you take some time to practice them.<\/p>\n\n\n\n\n\n\n\n
        SN.<\/th>\nFunction and brief description<\/th>\n<\/tr>\n
        1<\/td>\ncmp(dict1, dict2):\u00a0<\/strong>Compares elements of both dict but has been removed in Python 3.<\/td>\n<\/tr>\n
        2<\/td>\nlen(dict):\u00a0<\/strong>Returns the total length of the dictionary. This is the same as the number of items in the dictionary.<\/td>\n<\/tr>\n
        3<\/td>\nstr(dict):\u00a0<\/strong>Returns a printable string representation of\u00a0 the dictionary<\/td>\n<\/tr>\n
        4<\/td>\ntype(variable):\u00a0<\/strong>Gives the type of the variable passed. If the\u00a0 passed variable is a dictionary, then it would return a dictionary type.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
        Python includes following dictionary method<\/p>\n
         <\/p>\n
         <\/p>\n
        6. Dictionary Methods in Python<\/strong><\/h4>\n
        Python provides a number of useful methods you can use with dictionaries. These methods are given in the table below. I recommend you take some time to practice them. The video below this page can help you.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
        SN<\/th>\nMethods and brief description<\/th>\n<\/tr>\n
        1<\/td>\ndict.clear():\u00a0<\/strong>Deletes all elements of dictionary\u00a0dict<\/i><\/td>\n<\/tr>\n
        2<\/td>\ndict.copy():\u00a0<\/strong>Returns another copy of dictionary\u00a0dict<\/i><\/td>\n<\/tr>\n
        3<\/td>\ndict.fromkeys():\u00a0<\/strong>Create a new dictionary with keys from seq and values\u00a0set<\/i>\u00a0to\u00a0value<\/i>.<\/td>\n<\/tr>\n
        4<\/td>\ndict.get(key, default=None):\u00a0<\/strong>For the given\u00a0key<\/i>\u00a0key, returns value or default if key not in dictionary<\/td>\n<\/tr>\n
        5<\/td>\ndict.has_key(key):\u00a0<\/strong>Returns\u00a0true<\/i>\u00a0if key in dictionary\u00a0dict. Returns false if otherwise<\/i><\/td>\n<\/tr>\n
        6<\/td>\ndict.items():\u00a0<\/strong>Returns a list of the entries in a dictionary as\u00a0(key, value) tuple pairs<\/td>\n<\/tr>\n
        7<\/td>\ndict.keys():\u00a0<\/strong>Returns list of all the dictionary dict’s keys<\/td>\n<\/tr>\n
        8<\/td>\ndict.setdefault(key, default=None):\u00a0<\/strong>Similar to get(), but will set dict[key]=default if\u00a0key<\/i>\u00a0is not already in dict<\/td>\n<\/tr>\n
        9<\/td>\ndict.update(dict2):\u00a0<\/strong>Adds dictionary\u00a0dict2<\/i>‘s key-values pairs to\u00a0dict<\/i><\/td>\n<\/tr>\n
        10<\/td>\ndict.values():\u00a0<\/strong>Returns list of dictionary\u00a0dict<\/i>‘s values<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
        7. Watch the Video<\/strong><\/h4>\n