Convert comma to dot in Python or MySQL - mysql

Question

I have a Python script which collects data and sends it to my MySQL table.
I noticed that the "Cost" sometimes is 0,95 which results in 0 in my table since my table use "0.95" instead of "0,95".
I assume the best solution is to convert the , to . in my Python script by using:
variable.replace(",", ".")
However, couldn't one solution be to change format in my MySQL table? So that I store numbers in this format:
1100
0,95
0,1
150000
My Django Model
cost = models.DecimalField(max_digits=10, decimal_places=4, default=None)
Any feedback on how to best solve this issue?
Thanks

Answer 1

Your first instinct is correct: convert the "unusual" (comma-decimal) input into the standard format that MySQL used by default (dot-decimal) at the first point where you receive it.
there's lots of ways to write numbers
Be careful, though that you don't get stung by people using commas as thousands separators like "3,203,907.23", or the European form "3.203.907,23", the Swiss "3'203'907,23' or even this form, which is widely used in India: "32,03,907.71" (yes, I did mean to type only two digits there!)
To make your life easier, the rule for currencies is relatively simple:
where a dot or comma is followed by only two digits at the end of the string, that character is acting as the decimal separator.
Once you know which is the decimal separator, you can safely remove all other non-digits from the string, change the decimal separator you found to . then use any standard library string-to-number conversion.
Storage format isn't presentation format
Yes, you can tell MySQL to use comma as its decimal separator, but doing that will break so much of your code - including the parts of the framework that read from the database and expect dot-decimal numbers - that you'll regret doing it that way very quickly...
There's a general principle at work here: you should do your data storage and processing using a format that is easy to process, interchangeable with other systems, and understood by other software developers.
Consider what happens if you need to allow a different framework to access your MySQL database to generate reports... whoever develops that software (and it may be you) will be glad that the numbers are all stored the way numbers are "always" stored in databases.
Convert on the way in, re-convert on the way out
Where you need to accept input in a different format, convert that input into your standardised format as early as possible.
When you need to use an output format, do the conversion to that format as late as possible.
The idea is to keep as much of your system "unexceptional" as possible. A programmer who has to remember what numeric format will in force at the time when a given method is called is not a happy programmer.
P.S.
The option you're talking about in MySQL is an example of this pattern: it doesn't change how numeric data is stored. All that changes is how you pass numbers to MySQL and how it presents them back to you.