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Learning Python-Basic course: Day 18, Dictionaries in Python

Aatmaj
I'm a Computer Science enthusiast with a keen interest in Maths. I like to tinker with things around me & build projects on my own. I like to play musical instruments & practise Sahaja Yoga meditation
・3 min read

Welcome all🤟 Today we will cover dictionaries!


Dictionary is simply a collection of unordered key value pairs
Or sometimes referred as a 'hash table' of key value pairs. Dictionary holds key:value pair. this means that every value in an dictionary is mapped with some other value. Values in a dictionary can be of any datatype. Dictionaries cannot have two items with the same key for obvious reasons.
example

AatmajProfileDictionary={"name":"Aatmaj","Hobby":"teaching","Commits":700}
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Here is a quick difference between lists, tuples and dictionaries.
image

a=[] #list
a=() #tuple
a={}#dictionary
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Hash table

A Hash table is a data structure. A hash table is a data structure that implements an associative array abstract data type that can map keys to values. A hash table uses a hash function to compute an index also called as the hash code, into a array of buckets or slots, from which the desired value can be found.

As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

Sample program-

Here is a sample program just to get you started with dictionaries. It is quite easy to understand and commented whenever necessary

>>> hardware={    "Brand": "Dell",    "Model": 2430,    "Year":  "2020"}
>>> print(hardware) #prints the value of the dictionary
{'Brand': 'Dell', 'Model': 2430, 'Year': '2020'}
>>> print(hardware["Model"])
2430
>>> print(hardware.get("Model"))
2430
>>> hardware["Year"]=2021 #Changing the value of the dictionary
>>> print(hardware)
{'Brand': 'Dell', 'Model': 2430, 'Year': 2021}
>>> print(hardware.pop("Model"))
2430
>>> print(hardware)
{'Brand': 'Dell', 'Year': 2021}
>>> hardware["Model"]="Lenovo"
>>> hardware["Year"]=2019
>>> print(hardware.popitem()) #popitem returns the last value entered
('Model', 'Lenovo')
>>> print(hardware)
{'Brand': 'Dell', 'Year': 2019}
>>> for y in hardware:
...     print(y)#Corresponds to each key
...
Brand
Year
>>> for x in hardware:
...      print(hardware[x])#refers to the value
...
Dell
2019
>>> for z in hardware.values():
...      print(z)
...
Dell
2019
>>> hardware.clear() #Cleares the dictionary (not delete)
>>> print(hardware)
{}
>>> print(hardware["Price"])#trying to remove element which is not present
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'Price'
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Multidimensional dictionaries

Same story needs no explanation!

hardware={
    "LAPTOP":{"Brand": "Dell","Model": 2430,"Year":  "2020"},
    "DESKTOP":{"Brand":"Lenovo","Model":8877,"Warranty": 2},
    "TABLET":{"Brand":"Apple", "price":"3000$"}
}
print(hardware)
print(hardware["TABLET"])
print(hardware["LAPTOP"]["Model"]) #Note the syntax
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{'TABLET': {'price': '3000$', 'Brand': 'Apple'}, 'LAPTOP': {'Model': 2430, 'Brand': 'Dell', 'Year': '2020'}, 'DESKTOP': {'Model': 8877, 'Brand': 'Lenovo', 'Warranty': 2}}
{'price': '3000$', 'Brand': 'Apple'}
2430
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Exercise-
1) Make a dictionary which contains a list and a tuple. Then append the tuple in the list in the dictionary.

2) Dynamic generation of dictionaries- Write a program to take names of five students and their corresponding marks, put them in an dictionary.
output-

Please enter student name peter
Please enter marks 13
Please enter student name john
Please enter marks 32
Please enter student name pappu
Please enter marks 5
Please enter student name bob
Please enter marks 7
Please enter student name mina
Please enter marks 32
{'peter': 13, 'john': 32, 'pappu': 5, 'mina': 32, 'bob': 7}
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Answers will be found here

So friends that's all for this part. 😊For any suggestions please ping me🤠.
Here is my Gmail- aatmaj.mhatre@gmail.com 🤟
Don't forget to follow me on GitHub for updates on the course.😊

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