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Python : Dictionaries

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Emertxe Information Technologies Pvt Ltd
Emertxe Information Technologies Pvt Ltd

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 key:value pair. Key value is provided in the dictionary to make it more optimized. Each key-value pair in a Dictionary is separated by a colon :, whereas each key is separated by a ‘comma’. A Dictionary in Python works similar to the Dictionary in a real world. Keys of a Dictionary must be unique and of immutable data type such as Strings, Integers and tuples, but the key-values can be repeated and be of any type.

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Dictionaries Team Emertxe
Dictionaries Introduction Group of items arranged in the form of key-value pair Example d = {"Name": "Ram", "ID": 102, "Salary": 10000} Program #Print the entire dictionary print(d) #Print only the keys print("Keys in dic: ", d.keys()) #Print only values print("Values: ", d.values()) #Print both keys and value pairs as tuples print(d.items())
Dictionaries Operations d = {"Name": "Ram", "ID": 102, "Salary": 10000} 1. To get the no. of pairs in the Dictionary n = len(d) 2. To modify the existing value d[salary] = 15000 3. To insert new key:value pair d["Dept"] = "Finance" 4. To delete the key:value pair del d["ID"] 5. To check whether the key is present in dictionary "Dept" in d - Returns True, if it is present 6. We can use any datatype fro values, but keys should obey the rules R1: Keys should be unique Ex: emp = {10: "Ram", 20: "Ravi", 10: "Rahim"} - Old value will be overwritten, emp = {10: "Rahim", 20: "Ravi"} R2: Keys should be immutable type. Use numbers, strings or tuples If mutable keys are used, will get 'TypeError'
Dictionaries Methods clear() d.clear() Removes all key-value pairs from the d copy() d1 = d.copy() Copies all items from ‘d’ into a new dictionary ‘d1’ fromkeys() d.fromkeyss(s, [,v]) Create a new dictionary with keys from sequence ‘s’ and values all set to ‘v’ get() d.get(k, [,v]) Returns the value associated with key ‘k’. If key is not found, it returns ‘v’ items() d.items() Returns an object that contains key-value pairs of ‘d’. The pairs are stored as tuples in the object keys() d.keys() Returns a sequence of keys from the dictionary ‘d’ values() d.values() Returns a sequence of values from the dictionary ‘d’ update() d.update(x) Adds all elements from dictionary ‘x’ to ‘d’ pop() d.pop(k, [,v]) Removes the key ‘k’ and its value.
Dictionaries Programs To create the dictionary with employee details d = {"Name": "Ram", "ID": 1023, "Salary": 10000} #Print the entire dictionary print(d) #Print only the keys print("Keys in dic: ", d.keys()) #Print only values print("Values: ", d.values()) #Print both keys and value pairs as tuples print(d.items())
Dictionaries Programs #To create a dictionary from the keyboard and display the items x = {} print("Enter 'n' value: ", end='') n = int(input()) for i in range(n): print("Enter the key: ", end='') k = input() print("Enter the value: ", end='') v = int(input()) x.update({k: v}) print(x)
Dictionaries Using for loop with Dictionaries Method-1 for k in colors: print(k) Method-2 for k in colors: print(colors[k]) Method-3 for k, v in colors.items(): print("key = {}nValue = {}". format(k, v))
Dictionaries Sorting Dictionaries: Exercise To sort the elements of a dictionary based on akey or value
Dictionaries Converting Lists into Dictionary Two step procedure - zip() - dict() #To convert list into dictionary countries = ["India", "USA"] cities = ["New Delhi", "Washington"] #Make a dictionary z = zip(countries, cities) d = dict(z) print(d)
Dictionaries Converting strings into dictionary str = "Ram=23,Ganesh=20" #Create the empty list lst = [] for x in str.split(','): y = x.split('=') lst.append(y) #Convert into dictionary d = dict(lst) print(d)
Dictionaries Passing dictionary to function By specifying the name of the dictionary as the parameter, we can pass the dictionary to the function. Example d = {10: "Ram"} display(d)
Dictionaries Ordered Dictionaries from collections import OrderedDict Example d = {10: "Ram"} display(d) Program: #To create the ordered dictionary from collections import OrderedDict #Create empty dictionary d = OrderedDict() d[10] = 'A' d[11] = 'B' d[12] = 'C' d[13] = 'D' print(d)
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Python : Dictionaries

  • 2. Dictionaries Introduction Group of items arranged in the form of key-value pair Example d = {"Name": "Ram", "ID": 102, "Salary": 10000} Program #Print the entire dictionary print(d) #Print only the keys print("Keys in dic: ", d.keys()) #Print only values print("Values: ", d.values()) #Print both keys and value pairs as tuples print(d.items())
  • 3. Dictionaries Operations d = {"Name": "Ram", "ID": 102, "Salary": 10000} 1. To get the no. of pairs in the Dictionary n = len(d) 2. To modify the existing value d[salary] = 15000 3. To insert new key:value pair d["Dept"] = "Finance" 4. To delete the key:value pair del d["ID"] 5. To check whether the key is present in dictionary "Dept" in d - Returns True, if it is present 6. We can use any datatype fro values, but keys should obey the rules R1: Keys should be unique Ex: emp = {10: "Ram", 20: "Ravi", 10: "Rahim"} - Old value will be overwritten, emp = {10: "Rahim", 20: "Ravi"} R2: Keys should be immutable type. Use numbers, strings or tuples If mutable keys are used, will get 'TypeError'
  • 4. Dictionaries Methods clear() d.clear() Removes all key-value pairs from the d copy() d1 = d.copy() Copies all items from ‘d’ into a new dictionary ‘d1’ fromkeys() d.fromkeyss(s, [,v]) Create a new dictionary with keys from sequence ‘s’ and values all set to ‘v’ get() d.get(k, [,v]) Returns the value associated with key ‘k’. If key is not found, it returns ‘v’ items() d.items() Returns an object that contains key-value pairs of ‘d’. The pairs are stored as tuples in the object keys() d.keys() Returns a sequence of keys from the dictionary ‘d’ values() d.values() Returns a sequence of values from the dictionary ‘d’ update() d.update(x) Adds all elements from dictionary ‘x’ to ‘d’ pop() d.pop(k, [,v]) Removes the key ‘k’ and its value.
  • 5. Dictionaries Programs To create the dictionary with employee details d = {"Name": "Ram", "ID": 1023, "Salary": 10000} #Print the entire dictionary print(d) #Print only the keys print("Keys in dic: ", d.keys()) #Print only values print("Values: ", d.values()) #Print both keys and value pairs as tuples print(d.items())
  • 6. Dictionaries Programs #To create a dictionary from the keyboard and display the items x = {} print("Enter 'n' value: ", end='') n = int(input()) for i in range(n): print("Enter the key: ", end='') k = input() print("Enter the value: ", end='') v = int(input()) x.update({k: v}) print(x)
  • 7. Dictionaries Using for loop with Dictionaries Method-1 for k in colors: print(k) Method-2 for k in colors: print(colors[k]) Method-3 for k, v in colors.items(): print("key = {}nValue = {}". format(k, v))
  • 8. Dictionaries Sorting Dictionaries: Exercise To sort the elements of a dictionary based on akey or value
  • 9. Dictionaries Converting Lists into Dictionary Two step procedure - zip() - dict() #To convert list into dictionary countries = ["India", "USA"] cities = ["New Delhi", "Washington"] #Make a dictionary z = zip(countries, cities) d = dict(z) print(d)
  • 10. Dictionaries Converting strings into dictionary str = "Ram=23,Ganesh=20" #Create the empty list lst = [] for x in str.split(','): y = x.split('=') lst.append(y) #Convert into dictionary d = dict(lst) print(d)
  • 11. Dictionaries Passing dictionary to function By specifying the name of the dictionary as the parameter, we can pass the dictionary to the function. Example d = {10: "Ram"} display(d)
  • 12. Dictionaries Ordered Dictionaries from collections import OrderedDict Example d = {10: "Ram"} display(d) Program: #To create the ordered dictionary from collections import OrderedDict #Create empty dictionary d = OrderedDict() d[10] = 'A' d[11] = 'B' d[12] = 'C' d[13] = 'D' print(d)