Template function to convert ISBN-10s

[ownedbycats]

I found this code to convert ISBN-10s to 13s:

def check_digit_10(isbn):
    assert len(isbn) == 9
    sum = 0
    for i in range(len(isbn)):
        c = int(isbn[i])
        w = i + 1
        sum += w * c
    r = sum % 11
    if r == 10: return 'X'
    else: return str(r)

def check_digit_13(isbn):
    assert len(isbn) == 12
    sum = 0
    for i in range(len(isbn)):
        c = int(isbn[i])
        if i % 2: w = 3
        else: w = 1
        sum += w * c
    r = 10 - (sum % 10)
    if r == 10: return '0'
    else: return str(r)

def convert_10_to_13(isbn):
    assert len(isbn) == 10
    prefix = '978' + isbn[:-1]
    check = check_digit_13(prefix)
    return prefix + check

Would this be able to turned into a template function?

[chaley]

def evaluate(self, formatter, kwargs, mi, locals):
    isbn = mi.isbn
    if len(isbn) != 10:
        return 'isbn length != 10'
    prefix = '978' + isbn[:-1]
    check = self.check_digit_13(prefix)
    return prefix + check

def check_digit_13(self, isbn):
    assert len(isbn) == 12
    sum = 0
    for i in range(len(isbn)):
        c = int(isbn[i])
        if i % 2: w = 3
        else: w = 1
        sum += w * c
    r = 10 - (sum % 10)
    if r == 10: return '0'
    else: return str(r)

[ownedbycats]

Yes, that's where I figured to put it. Should've bee a little more clear. What I'm a bit confused on is whether it could be plugged into a template (presumably Action Chains' single-field edit) to convert an identifier from isbn10 to 13.

[chaley]

Originally Posted by ownedbycats

Yes, that's where I figured to put it. Should've bee a little more clear. What I'm a bit confused on is whether it could be plugged into a template (presumably Action Chains' single-field edit) to convert an identifier from isbn10 to 13.

Sure. It is a template function like any other. You just make a GPM template to call it.

program: whatever_you_called_it()

You could instead make it a stored template instead of a template function.

Example:


This template is slightly different from the function above, correcting a bug and making it return the existing isbn if it isn't 10 long.

def evaluate(book, context):
	isbn = book.identifiers.get('isbn', '')
	if len(isbn) != 10:
		# This isn't an isbn 10. Return it as it is.
		return isbn
	prefix = '978' + isbn[:-1]
	check = check_digit_13(prefix)
	return prefix + check

def check_digit_13(isbn):
	sum = 0
	for i in range(len(isbn)):
		c = int(isbn[i])
		if i % 2: w = 3
		else: w = 1
		sum += w * c
	r = 10 - (sum % 10)
	if r == 10: return '0'
	else: return str(r)

Call it with

program: isbn10_to_13()

[ownedbycats]

Thanks.

When trying to get the new ISBN back into the identifiers field, I tried this:

program: 

	isbn = columnupdate_identifier_isbnconvert();
	
	newisbn = strcat('isbn:', isbn);

	list_union($identifiers, newisbn, ',')

Template tester shows it producing a result of
isbn:9780690042399, goodreads:2152001, isbn:0690042396

However, actually running it fails, I think because the identifiers field won't accept the isbn value when one already exists. What would be the best option for either

a) instead of list_union, replacing the ISBN;
b) removing the existing ISBN before doing the list_union?

I thought list_re should work, but I'm having trouble with the syntax.

[chaley]

Here are two solutions, one in GPM and one in Python.

program: 
	new_ids = '';
	found_isbn = '';

# first search for an isbn. Remove it from the list if found.
	for id in $identifiers:
		if '^isbn:' in id then
			found_isbn = '1'
		else
# Can't use list operations because ids can contain commas
			new_ids = new_ids & (if new_ids then ', ' fi) & id
  		fi
	rof;

# If we found an isbn try to convert it and then add it back into the identifiers list
	if found_isbn then
		isbn = isbn10_to_13();
		newisbn = strcat('isbn:', isbn);
		new_ids & (if new_ids then ', ' fi) & newisbn
	else
		$identifiers
	fi

Here is a solution in Python. This will be much faster but probably harder for you to understand what it does. It doesn't use the stored template, instead including the conversion functions directly.

python:
def evaluate(book, context):
	new_ids = {}
	# Copy the identifiers dict, replacing isbns with the converted value
	for k,v in book.identifiers.items():
		new_ids[k] = convert_isbn(v) if k == 'isbn' else v
	# Rebuild the identifiers string from the new identifiers dict
	return ', '.join([k + ':' + v for k,v in new_ids.items()])
		
def convert_isbn(isbn):
	if len(isbn) != 10:
		# This isn't an isbn 10. Return it as it is.
		return isbn
	prefix = '978' + isbn[:-1]
	check = check_digit_13(prefix)
	return prefix + check

def check_digit_13(isbn):
	sum = 0
	for i in range(len(isbn)):
		c = int(isbn[i])
		if i % 2: w = 3
		else: w = 1
		sum += w * c
	r = 10 - (sum % 10)
	if r == 10: return '0'
	else: return str(r)

[ownedbycats]

Oh, I didn't realize about the list ops not working for ids. That's useful to know in the future. Thanks.