====== Python Data Structures ======




===== Summary ====

[ ] = [[python:python-data-struct#list|List]] \\
{ } = [[python:python-data-struct#dictionary|Dictionary]] \\
( ) = [[python:python-data-struct#tuple|Tuple]] \\

Boolean:- [[python:python-data-struct#boolean_true_of_false]] \\

===== List =====

Identified by square brackets and uses comma as seperator between elements. A list element is looked up by it's position in the list.

<code python>
list = ['value1', 'value2']
</code>

Remember, list indices start at ''0''!!
To get the first item, start with the index 0:-

<code python>
firstitem = list[0] 
</code>

Add a new item to the end of the list with:-

<code python>
list.append(value3)
</code>

Add a new item in the middle:-

<code python>
list.insert(value2)
</code>


Select the last item in a list, this example splits a file url on directory separator (''/''), and selects the last item which should be the filename. Won't work on windows, but who cares!!

<code python>
fileName = key.split('/')[-1]
</code>

Iterate over a list
<code python>
# for loop
for index in list:
    print(index)
</code>

===== Dictionary =====

Identified by curly brackets and uses ":" to seperate out a Key and a Value. A value in a dictionary is referenced by it's key, the actual order of items stored in a dictionary can change, so you cannot retreive a value based on the position if you just print out the whole dictionary, you **have** to use the key.


<code python>
dict = { "key1": "value1", "key2": "value2" }
</code>

If you want to look up the meaning of a word in English, you use a Dictionary to find the word (Key) and then read out the meaning of the word (Value).

<code python>
wordlist = { 
  'obfuscate': 'to make something less clear and harder to understand, especially intentionally',  
  'clarify': 'to make something clear or easier to understand by giving more details' 
}
</code>

So:-
<code python>
definition = wordlist['obfuscate']
</code>

returns '' to make something less clear and harder to understand, especially intentionally ''


As a dictionary is referenced by it's key to get a value, adding a new element is as easy as just creating a new key:value pair, there is no concept of insert as with a list.

<code python>
wordlist.update({'understand':'to know the meaning of something that someone says'})
wordlist['difficult'] = 'needing skill or effort'
</code>


Testing if a key exists in a dictionary, ''key in dictionary'' evaluates to true or false:-
<code python>
if record["Key1"] in record:
    record["Key2"] = record["Key1"]
</code>


Print just keys:-
<code python>
print(dictionary.keys())
</code>

Print all keys and values in a dictionary:-

<code python>
for key in dict:
    print(key, dict[key])
</code>


Print out each key/value line by line:-

<code python>
for key, value in get_metadata_response.items():
        print(key, ' : ', value)   
</code>


Testing keys, check if a dictionary contains a specified key:-

<code python>
if 'user_a' in metadata.keys():
    print("user_a supplied")             
elif 'user_b' in metadata.keys():
    print("user_b supplied")
else:
    print('Neither user A or B')
</code>


===== Tuple =====

A tuples is an immutable sequence. This means you cannot change it after it is created.

<code python>
tuple = (a, b, c)
</code>


===== Strings =====

In Python a string is a [[python:python-data-struct#list|list]] so you can address individual elements in it using list notation.

So to select a portion of a string you can address each character as a list element:-

<code python>
account = '445156287145'
removechar = 8

result1 = account[removechar:]

result2 = account[removechar:len(account)]

print(result1, result2)
</code>
  7145 7145


===== List of dictionaries =====

<code python>
listOfDict = [ {'foo':1,'bar':123},
  	     {'boo':3,'mar':234},
	     {'moo':5,'par':345} ]
</code>


===== Boolean True of False =====

Booleans are either "True or False"


        # Add user to user_model table, sql code to add new row OR update existing one:-
        # https://stackoverflow.com/questions/15383852/sql-if-exists-update-else-insert-into
        user_model_sql = f'''
        insert into user_model(highside_user_id, login_status)
        values ('{hsusername}', true)
        on duplicate key
        update highside_user_id = values(highside_user_id), login_status = values(login_status);
        '''
        
mysql_query = f"SELECT IF(login_status, 'true', 'false') from user_model WHERE highside_user_id = '{sessionname}'; "