Function mode for Search & replace in the Editor

The Search & replace tool in the editor support a function mode. In this mode, you can combine regular expressions (see All about using regular expressions in calibre) with arbitrarily powerful Python functions to do all sorts of advanced text processing.

In the standard regexp mode for search and replace, you specify both a regular expression to search for as well as a template that is used to replace all found matches. In function mode, instead of using a fixed template, you specify an arbitrary function, in the Python programming language. This allows you to do lots of things that are not possible with simple templates.

Techniques for using function mode and the syntax will be described by means of examples, showing you how to create functions to perform progressively more complex tasks.

Automatically fixing the case of headings in the document

Here, we will leverage one of the builtin functions in the editor to automatically change the case of all text inside heading tags to title case:

Find expression: <([Hh][1-6])[^>]*>.+?</\1>

For the function, simply choose the Title-case text (ignore tags) builtin function. The will change titles that look like: <h1>some titLE</h1> to <h1>Some Title</h1>. It will work even if there are other HTML tags inside the heading tags.

Your first custom function - smartening hyphens

The real power of function mode comes from being able to create your own functions to process text in arbitrary ways. The Smarten Punctuation tool in the editor leaves individual hyphens alone, so you can use the this function to replace them with em-dashes.

To create a new function, simply click the Create/edit button to create a new function and copy the Python code from below.

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    return match.group().replace('--', '—').replace('-', '—')

Every Search & replace custom function must have a unique name and consist of a Python function named replace, that accepts all the arguments shown above. For the moment, we won’t worry about all the different arguments to replace() function. Just focus on the match argument. It represents a match when running a search and replace. Its full documentation in available here. match.group() simply returns all the matched text and all we do is replace hyphens in that text with em-dashes, first replacing double hyphens and then single hyphens.

Use this function with the find regular expression:

>[^<>]+<

And it will replace all hyphens with em-dashes, but only in actual text and not inside HTML tag definitions.

The power of function mode - using a spelling dictionary to fix mis-hyphenated words

Often, e-books created from scans of printed books contain mis-hyphenated words – words that were split at the end of the line on the printed page. We will write a simple function to automatically find and fix such words.

import regex
from calibre import replace_entities
from calibre import prepare_string_for_xml

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):

    def replace_word(wmatch):
        # Try to remove the hyphen and replace the words if the resulting
        # hyphen free word is recognized by the dictionary
        without_hyphen = wmatch.group(1) + wmatch.group(2)
        if dictionaries.recognized(without_hyphen):
            return without_hyphen
        return wmatch.group()

    # Search for words split by a hyphen
    text = replace_entities(match.group()[1:-1])  # Handle HTML entities like &
    corrected = regex.sub(r'(\w+)\s*-\s*(\w+)', replace_word, text, flags=regex.VERSION1 | regex.UNICODE)
    return '>%s<' % prepare_string_for_xml(corrected)  # Put back required entities

Use this function with the same find expression as before, namely:

>[^<>]+<

And it will magically fix all mis-hyphenated words in the text of the book. The main trick is to use one of the useful extra arguments to the replace function, dictionaries. This refers to the dictionaries the editor itself uses to spell check text in the book. What this function does is look for words separated by a hyphen, remove the hyphen and check if the dictionary recognizes the composite word, if it does, the original words are replaced by the hyphen free composite word.

Note that one limitation of this technique is it will only work for mono-lingual books, because, by default, dictionaries.recognized() uses the main language of the book.

Auto numbering sections

Now we will see something a little different. Suppose your HTML file has many sections, each with a heading in an <h2> tag that looks like <h2>Some text</h2>. You can create a custom function that will automatically number these headings with consecutive section numbers, so that they look like <h2>1. Some text</h2>.

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    section_number = '%d. ' % number
    return match.group(1) + section_number + match.group(2)

# Ensure that when running over multiple files, the files are processed
# in the order in which they appear in the book
replace.file_order = 'spine'

Use it with the find expression:

(?s)(<h2[^<>]*>)(.+?</h2>)

Place the cursor at the top of the file and click Replace all.

This function uses another of the useful extra arguments to replace(): the number argument. When doing a Replace All number is automatically incremented for every successive match.

Another new feature is the use of replace.file_order – setting that to 'spine' means that if this search is run on multiple HTML files, the files are processed in the order in which they appear in the book. See Choose file order when running on multiple HTML files for details.

Auto create a Table of Contents

Finally, lets try something a little more ambitious. Suppose your book has headings in h1 and h2 tags that look like <h1 id="someid">Some Text</h1>. We will auto-generate an HTML Table of Contents based on these headings. Create the custom function below:

from calibre import replace_entities
from calibre.ebooks.oeb.polish.toc import TOC, toc_to_html
from calibre.gui2.tweak_book import current_container
from calibre.ebooks.oeb.base import xml2str

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    if match is None:
        # All matches found, output the resulting Table of Contents.
        # The argument metadata is the metadata of the book being edited
        if 'toc' in data:
            toc = data['toc']
            root = TOC()
            for (file_name, tag_name, anchor, text) in toc:
                parent = root.children[-1] if tag_name == 'h2' and root.children else root
                parent.add(text, file_name, anchor)
            toc = toc_to_html(root, current_container(), 'toc.html', 'Table of Contents for ' + metadata.title, metadata.language)
            print(xml2str(toc))
        else:
            print('No headings to build ToC from found')
    else:
        # Add an entry corresponding to this match to the Table of Contents
        if 'toc' not in data:
            # The entries are stored in the data object, which will persist
            # for all invocations of this function during a 'Replace All' operation
            data['toc'] = []
        tag_name, anchor, text = match.group(1), replace_entities(match.group(2)), replace_entities(match.group(3))
        data['toc'].append((file_name, tag_name, anchor, text))
        return match.group()  # We don't want to make any actual changes, so return the original matched text

# Ensure that we are called once after the last match is found so we can
# output the ToC
replace.call_after_last_match = True
# Ensure that when running over multiple files, this function is called,
# the files are processed in the order in which they appear in the book
replace.file_order = 'spine'

And use it with the find expression:

<(h[12]) [^<>]* id=['"]([^'"]+)['"][^<>]*>([^<>]+)

Run the search on All text files and at the end of the search, a window will popup with “Debug output from your function” which will have the HTML Table of Contents, ready to be pasted into toc.html.

The function above is heavily commented, so it should be easy to follow. The key new feature is the use of another useful extra argument to the replace() function, the data object. The data object is a Python dictionary that persists between all successive invocations of replace() during a single Replace All operation.

Another new feature is the use of call_after_last_match – setting that to True on the replace() function means that the editor will call replace() one extra time after all matches have been found. For this extra call, the match object will be None.

This was just a demonstration to show you the power of function mode, if you really needed to generate a Table of Contents from headings in your book, you would be better off using the dedicated Table of Contents tool in Tools → Table of Contents.

The API for the function mode

All function mode functions must be Python functions named replace, with the following signature:

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    return a_string

When a find/replace is run, for every match that is found, the replace() function will be called, it must return the replacement string for that match. If no replacements are to be done, it should return match.group() which is the original string. The various arguments to the replace() function are documented below.

The match argument

The match argument represents the currently found match. It is a Python Match object. Its most useful method is group() which can be used to get the matched text corresponding to individual capture groups in the search regular expression.

The number argument

The number argument is the number of the current match. When you run Replace All, every successive match will cause replace() to be called with an increasing number. The first match has number 1.

The file_name argument

This is the filename of the file in which the current match was found. When searching inside marked text, the file_name is empty. The file_name is in canonical form, a path relative to the root of the book, using / as the path separator.

The metadata argument

This represents the metadata of the current book, such as title, authors, language, etc. It is an object of class calibre.ebooks.metadata.book.base.Metadata. Useful attributes include, title, authors (a list of authors) and language (the language code).

The dictionaries argument

This represents the collection of dictionaries used for spell checking the current book. Its most useful method is dictionaries.recognized(word) which will return True if the passed in word is recognized by the dictionary for the current book’s language.

The data argument

This a simple Python dictionary. When you run Replace all, every successive match will cause replace() to be called with the same dictionary as data. You can thus use it to store arbitrary data between invocations of replace() during a Replace all operation.

The functions argument

The functions argument gives you access to all other user defined functions. This is useful for code re-use. You can define utility functions in one place and re-use them in all your other functions. For example, suppose you create a function name My Function like this:

def utility():
   # do something

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    ...

Then, in another function, you can access the utility() function like this:

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    utility = functions['My Function']['utility']
    ...

You can also use the functions object to store persistent data, that can be re-used by other functions. For example, you could have one function that when run with Replace All collects some data and another function that uses it when it is run afterwards. Consider the following two functions:

# Function One
persistent_data = {}

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    ...
    persistent_data['something'] = 'some data'

# Function Two
def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    persistent_data = functions['Function One']['persistent_data']
    ...

Debugging your functions

You can debug the functions you create by using the standard print() function from Python. The output of print will be displayed in a popup window after the Find/replace has completed. You saw an example of using print() to output an entire table of contents above.

Choose file order when running on multiple HTML files

When you run a Replace all on multiple HTML files, the order in which the files are processes depends on what files you have open for editing. You can force the search to process files in the order in which the appear by setting the file_order attribute on your function, like this:

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    ...

replace.file_order = 'spine'

file_order accepts two values, spine and spine-reverse which cause the search to process multiple files in the order they appear in the book, either forwards or backwards, respectively.

Having your function called an extra time after the last match is found

Sometimes, as in the auto generate table of contents example above, it is useful to have your function called an extra time after the last match is found. You can do this by setting the call_after_last_match attribute on your function, like this:

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    ...

replace.call_after_last_match = True

Appending the output from the function to marked text

When running search and replace on marked text, it is sometimes useful to append so text to the end of the marked text. You can do that by setting the append_final_output_to_marked attribute on your function (note that you also need to set call_after_last_match), like this:

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    ...
    return 'some text to append'

replace.call_after_last_match = True
replace.append_final_output_to_marked = True

Suppressing the result dialog when performing searches on marked text

You can also suppress the result dialog (which can slow down the repeated application of a search/replace on many blocks of text) by setting the suppress_result_dialog attribute on your function, like this:

def replace(match, number, file_name, metadata, dictionaries, data, functions, *args, **kwargs):
    ...

replace.suppress_result_dialog = True

More examples

More useful examples, contributed by calibre users, can be found in the calibre E-book editor forum.

© Copyright Kovid Goyal. Last updated on Oct 18, 2024.