Generate a sequence in Python for barcoding items

Question

I am trying to generate barcodes in an app to tag the products which includes 3 things:

1. Batch no. (GRN ID)
2. Product ID
3. serial ID

Something like this:

 def get(self, request, *args, **kwargs):
        pk = self.kwargs['pk']
        grn = Grn.objects.filter(pk=pk)[0]
        grn_prod = grn.items.all()
        items = []
        for i in grn_prod:
            for j in range(i.item_quantity):
                items.append("YNT" + str(pk) + str(i.item.pk) + str(j + 1))  

It generates a sequence like the following:

YNT55232

Which is good but while scanning it if I want to know the item ID or Serial ID the it becomes a problem as it could be 23, 523, 3, etc.

For this I want to specify a no of digits for GRN , Product and Serial Id something like this:

GRN Barcode     GRN ID  Product ID  Serial ID
            YNT  000X     000X       0000X

I am unable to figure out how to append 0 before the IDs ?

Answer 1

you can use format in Python. It is commonly used to format many variables.

If you want to format this: "YNT" + str(pk) + str(i.item.pk) + str(j + 1) you can use format as below:

'"YNT"\t{:04d}\t{:04d}\t{:05d}'.format(pk, i.item.pk, j+1)

In case you do not know; the {} are for each variable as in order in format() .

As you want to have pk and i.item.pk as four characters, then you add :04d . :04d completes the words with 0. For instance;

if pk = 1 , then it converts it to 0001 , or if it is 101 then it converts to 0101 .

Same is for j+1 , if j+1 is 1, then it generates 00001 , if it is 101 , then it generates 00101 .

If you have not used format in Python, I suggest you learn it. It is really helpful for formatting variables.

Answer 2

Thezfill function does exactly this. str.zfill(5) will pad given string in variable str to at least 5 characters, for example.

Answer 3

There are different ways to achieve String formatting .

%-formatting

Look at the above mention documentation of string function zfill . A box follows that explains:

printf style String Formatting using the % operator (modulo):

barcode = '%(gnr)03d%(product)03d%(serial)04d' % {'gnr': 123, 'product': 456, 'serial': 7890}

print(barcode)

produces YNT1234567890 .

f-strings (since Python 3.6)

You can also use the Python 3 way with f-strings :

# barcode components readable named
gnr = pk
product = i.item.pk
serial = j + 1

#  format-literal simply will replace the variables named
barcode = f"YNT{gnr:03}{product:03}{serial:04}"

items.append(barcode)

It uses a prefix after the variable-name:

• :0x for left-padding with x leading zeros.

---

Note: I always clearly named the template-variables (here: barcode components):

• put in a map with descriptive keys (like above in %-formatting)
• put in separate variables with names describing each of them (like in f-string example)

So we can use a readable template also called format-literal like: "{component_1} before {component_2} then {the_rest}"