Converting Pandoc Markdown images from captioned to inline

Question

After writing a rather long document in Markdown and using pandoc to convert it to a PDF, I found, to my dismay, that many of the images were out of place, and that they all had their alternate text proudly displayed underneath them as captions. My document is rather instructional, so this rearrangement was harmful to its readability.

I eventually found a way to display the images as inline. I still wanted to write the document in standard Markdown, though, so I wrote a Python script to convert all the standalone images in a document to this inline form.

pandoc_images.py:

import sys

# Convert standalone images in standard Markdown
# to inline images in Pandoc's Markdown
# (see http://pandoc.org/README.html#images)
with open(sys.argv[1], 'r') as markdown:
    lines = markdown.read().splitlines()
    for index, line in enumerate(lines):
        is_first_line = index == 0
        preceding_blank = True if is_first_line else not lines[index - 1]

        is_last_line = index == len(lines) - 1
        following_blank = True if is_last_line else not lines[index + 1]

        is_standalone = preceding_blank and following_blank
        is_image = line.startswith('![') and '](' in line and line.endswith(')')
        print(line + ('\\\n' if is_standalone and is_image else ''))

Example (text.md):

This is some text.

![This is an image.](image.png)

### This is a header.

Running python3 pandoc_images.py text.md would produce:

This is some text.

![This is an image.](image.png)\


### This is a header.

It seems like a lot of mess (enumerate, bounds checking, etc.) for such a simple job, though. Is there any way I can improve any of this code?

Answer 1

Instead of a ternary, use the or syntax for setting your booleans here. If is_first_line is True then True is returned, if it's not then not lines[index - 1] is evaluated and the result of that is returned whether it's True or False.

preceding_blank = is_first_line or not lines[index - 1]

But since you're setting is_first_line one line before and never using it again, I'd even fold that into this expression.

preceding_blank = index == 0 or not lines[index - 1]

I'd make both the same changes with is_last_line. Also I would substitute index for i, since i is idiomatic for index anyway and will save some characters.

One last thing that you may want, adding .strip() to not line will strip out any whitespace on the line and make sure that even an empty whitespace line will be considered False because any character in a string will make it evaluate as True. This may or may not be beneficial to you, as whitespace could be meaningful.

with open(sys.argv[1], 'r') as markdown:
    lines = markdown.read().splitlines()
    for i, line in enumerate(lines):
        precedingBlank = i == 0 or not lines[i - 1].strip()
        followingBlank = i == len(lines) - 1 or not lines[i + 1].strip()
        is_standalone = preceding_blank and following_blank

        is_image = line.startswith('![') and '](' in line and line.endswith(')')
        print(line + ('\\\n' if is_standalone and is_image else ''))

Answer 2

How about a regular expression?

def convert(s):
  return re.sub(r"((?:\A|^ *\n)!\[.*\]\(.*\))\n(^ *\n|\Z)", r"\1\\\2", s, 0, re.M)

def test1():
  print convert("""![foo](bar)\n\nthis is a test\n""")

def test2():
  print convert("""line 1\n\n![foo](asd)\n\nanother test\n""")

def test3():
  print convert("""line 1\n\n![foo](asd)\n""")

def test4():
  print convert("""line 1\n\n![foo](asd)\nNot blank\n""")

Note: I am using ^\s*\n to match a blank line - i.e. it can also contain spaces.

Answer 3

You could make your code more reusable (for example, from another Python program) by making it into a function. The descriptive comment would then naturally be the docstring of this function, which allows it to be accessed by other tools, like the help function in an interactive Python session, or the pydoc command-line tool.

To allow both using the function from another program (by importing it) and running it as a standalone script, use the __name__ == '__main__' idiom.

Concerning opening a file, 'r' is the default mode and does not need to be specified.

So, change this:

import sys

# Convert standalone images in standard Markdown
# to inline images in Pandoc's Markdown
# (see http://pandoc.org/README.html#images)
with open(sys.argv[1], 'r') as markdown:
    # ... process lines ...

To this:

def inline_images(markdown):
    """
    Convert standalone images in standard Markdown contained in the
    open file "markdown" to inline images in Pandoc's Markdown
    (see http://pandoc.org/README.html#images).
    """
    # ... process lines ...

if __name__ == '__main__':
    import sys
    with open(sys.argv[1]) as markdown:
        inline_images(markdown)