Day 49: Python understanding data dictionaries
Data Dictionary
We touch the concept of associative arrays today.
This is another name for data dictionary.
Definition
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
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'])
print(students['cvelvindron'])
The equivalent in SQL would be:
select * from students where id='cvelvindron';
Length of dictionary
#len(dictionaryname)
len(students)
==> 4
Check if exists
print ('smell' in students)
print ('cvelvindron' in students)
False
True
Get data from dict
#Syntax: dictionaryname.get(key)
#exist
print (students.get('cvelvindron'))
#not exist
print (students.get('manone'))
Get data from dict with custom error
#Syntax: dictionaryname.get(key, custommessage)
#exist
print (students.get('cvelvindron', 'Unknown?'))
#not exist
print (students.get('manone', 'Unknown?'))
Here, we added ‘Unknown?’ instead of the default ‘None’.
Changing the value of a key
#Syntax: dictionaryname[key] = newvalue
students[cvelvindron] = 'Codarren Valaydon Velvindron'
print (students.get('cvelvindron', 'Unknown?'))
Adding or updating dictionary data
#Syntax: dictionaryname.update({key:value})
students.update('cvelvindron':'Codax Devildron')
print (students.get('cvelvindron', 'Unknown?'))
