Dictionariesasdfghjsdfghjklsdfghjkl.pptx

Dictionariesasdfghjsdfghjklsdfghjkl.pptx

• 1.
  Dictionaries
• 2.
  Introduction • A dictionaryis a container object that stores a collection of key/value pairs. It enables fast retrieval, deletion, and updating of the value by using the key. • A dictionary is an efficient data structure for such a task. • A dictionary is a collection that A dictionary is an efficient data structure for such a task. • A dictionary is a collection that stores the values along with the keys. • The keys are like an index operator. In a list, the indexes are integers. • In a dictionary, the key must be a hashable object. A dictionary cannot contain duplicate keys. • A dictionary is also known as a map, which maps each key to a value. • Each key maps to one value. A key and its corresponding value form an item (or entry) stored in a dictionary, as shown in Figure 14.1a.
• 3.
  Contd..
• 4.
  What is aDictionary? • Dictionary in Python is an unordered collection of data values, used to store data values like a map, which unlike other Data Types that hold only single value as an element. • Dictionary holds a pair of values, one being the Key and the other corresponding pair element being its key-value.
• 5.
  What is aDictionary? • Dictionary in Python is an unordered collection of data values, used to store data values like a map, which unlike other Data Types that hold only single value as an element. • A dictionary is a collection which is unordered, changeable and indexed • Values in a dictionary can be of any data type and can be duplicated, whereas keys can’t be repeated and must be immutable. • Key value is provided in the dictionary to make it more optimized.
• 6.
  Creating a Dictionary •n Python, a Dictionary can be created by placing sequence of elements within curly “{ }” braces, separated by ‘comma’. • Dictionary keys are case sensitive, same name but different cases of Key will be treated distinctly.
• 8.
  Creating empty dictionary
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  Creating dictionary usingdict() function • We can create dictionaries by using a builtin function called dict().
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  Adding and replacingvalues to a dictionary • To add new items in to a dictionary , we can use the subscript [] operator. • Syntax: Dictioanry_name [key] = value
• 11.
  Adding and replacingvalues to a dictionary
• 12.
  Replacing value ofdictionary
• 13.
  Formatting dictionaries • The% operator is used to substitute values from a dictionary , in to a string by using key.
• 14.
  Deleting items fromdictionary • We can delete any entry from dictionary. • The “del” operator is used to remove key and its associated value. • If key is found in the dictionary then it is removed otherwise python raises an error. • Syntax: del dictioanry_name[key]
• 15.
  Deleting items fromdictionary
• 16.
  The len Function •You can find the number of the items in a dictionary by using len(dictionary). For example.
• 17.
  Testing Whether aKey Is in a Dictionary • You can use the in or not in operator to determine whether a key is in the dictionary. For example:
• 18.
  Equality Test (or)Comparingtwo dictionaries • The “==” operator is used to test if two dictionaries contains the same items. • It returns true two dictionaries contains same items. • Similarly the “!=” operator is used to test if two dictionaries doesn’t contain same items. • It returns true two dictionaries contains different items.
• 19.
  example
• 20.
  Comparing two dictionaries
• 21.
  The Dictionary Methods •The Python class for dictionaries is dict. Figure 14.2 lists the methods that can be invoked from a dictionary object
• 22.
  • The get(key)method is similar to dictionaryName[key] except that the get method returns None if the key is not in the dictionary rather than raising an exception. • The pop(key) method is the same as del dictionaryName[key]. Here are some examples that show these methods in use:
• 23.
  The methods ofdictionary class • keys() – return a sequence of keys from dictionary
• 24.
  The methods ofdictionary class • values() – return a sequence of vales from a dictionary
• 25.
  The methods ofdictionary class • items() – Return a sequence of tuples
• 26.
  The methods ofdictionary class • get(key) – return the value for key.
• 27.
  The methods ofdictionary class • clear() – Delete all entries of a dictionary
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  Traversing dictionaries • Thefor loop is used to traverse all keys and values of a dictionary. • The variable of the for loop is bound to each key in an unspecified order. • It means it retrieve the keys and values in any order.
• 29.
  Traversing dictionaries usingfor loop
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  Nested dictionaries • Adictionary with in a dictionary is called nested dictionary.
• 31.
  Traversing Nested dictionaries
• 32.
  Polynomials as dictionaries •Dictionaries can change their content so they are mutable in nature. • The keys in a dictionary is not restricted to be strings. • Any immutable object can be used as key. • A common type of key used in dictionaries is integers. • We can use dictionaries while calculating polynomial equation. • A dictionary is used to map a power to a coefficient. let the equation be -2 + y^4 + 3y^6 The dictionary for the above equation is {0:-2, 4:1, 6:3}
• 33.
  Write a pythonprogram to calculate the polynomial equation -2 + y^4 + 3y^6