Day 49: Python understanding data dictionaries

Data Dictionary

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We touch the concept of associative arrays today.

This is another name for data dictionary.


A data dictionary is pretty much like a table in which the first column is the key (we can think of it as the primary key in DBs)

Why ?

We use data dictionaries to store data where each piece of data share some kind of relation to each other.

How ?

we have to have a dictionary name.

Let’s say in this case we have a students dictionary.

students = {
'cvelvindron': 'Codarren Velvindron',
'jsnow': 'Jon Snow',
'rvazilito': 'Razor Vazilito',
'harvshrew': 'Harv Shrew',
print (students)

Output create dictionary python

Thoughts We can see the concept of key-value pair.

cvelvindron is my key (and as such, it is unique.

To see values of a key

#print (dictionaryname['key'])

The equivalent in SQL would be:

select * from students where id='cvelvindron';

Length of dictionary

==> 4

Check if exists

print ('smell' in students)
print ('cvelvindron' in students)

Get data from dict

#Syntax: dictionaryname.get(key)
print (students.get('cvelvindron'))
#not exist
print (students.get('manone'))

get data from dictionary

Get data from dict with custom error

#Syntax: dictionaryname.get(key, custommessage)
print (students.get('cvelvindron', 'Unknown?'))
#not exist
print (students.get('manone', 'Unknown?'))

Here, we added ‘Unknown?’ instead of the default ‘None’.

custom message data dictionary

Changing the value of a key

#Syntax: dictionaryname[key] = newvalue
students[cvelvindron] = 'Codarren Valaydon Velvindron'
print (students.get('cvelvindron', 'Unknown?'))

change dict value python

Adding or updating dictionary data

#Syntax: dictionaryname.update({key:value})
students.update('cvelvindron':'Codax Devildron')
print (students.get('cvelvindron', 'Unknown?'))

update key value python

That’s all folks!


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\ Codarren /

Written on February 18, 2021