Python Code to Write to file with Left and Right Margins and Fixed Line Length

Question

I am writing a Python program that reads a file and then writes its contents to another one, with added margins. The margins are user-input and the line length must be at most 80 characters.

I wrote a recursive function to handle this. For the most part, it is working. However, the 2 lines before any new paragraph display the indentation that was input for the right side, instead of keeping the left indentation. Any clues on why this happen?

Here's the code:

left_Margin = 4
right_Margin = 5

# create variable to hold the number of characters to withhold from line_Size
avoid = right_Margin
num_chars = left_Margin


def insertNewlines(i, line_Size):
    string_length = len(i) + avoid + right_Margin
    if len(i) <= 80 + avoid + left_Margin:
        return i.rjust(string_length)
    else:
        i = i.rjust(len(i)+left_Margin)
        return i[:line_Size] + '\n' + ' ' * left_Margin + insertNewlines(i[line_Size:], line_Size)

with open("inputfile.txt", "r") as inputfile:
    with open("outputfile.txt", "w") as outputfile:
        for line in inputfile:
            num_chars += len(line)
            string_length = len(line) + left_Margin
            line = line.rjust(string_length)
            words = line.split()
            # check if num of characters is enough
            outputfile.write(insertNewlines(line, 80 - avoid - left_Margin))

For input of left_Margin=4 and right_Margin = 5, I expect this:

____Poetry is a form of literature that uses aesthetic and rhythmic
____qualities of language—such as phonaesthetics, sound symbolism, and
____metre—to evoke meanings in addition to, or in place of, the prosai
____c ostensible meaning. 
____Poetry has a very long history, dating back to prehistorical ti
____mes with the creation of hunting poetry in Africa, and panegyric an
____d elegiac court poetry was developed extensively throughout the his
____tory of the empires of the Nile, Niger and Volta river valleys.

But The result is:

     ____Poetry is a form of literature that uses aesthetic and rhythmic
     ______qualities of language—such as phonaesthetics, sound symbolism, and
     ______metre—to evoke meanings in addition to, or in place of, the prosai
          ________c ostensible meaning. 
    _____Poetry has a very long history, dating back to prehistorical ti
    _____mes with the creation of hunting poetry in Africa, and panegyric an
    _____d elegiac court poetry was developed extensively throughout the his
          _____tory of the empires of the Nile, Niger and Volta river valleys.

Answer 1

This isn't really a good fit for a recursive solution in Python. Below is an imperative/iterative solution of the formatting part of your question (I'm assuming you can take this and write it to a file instead). The code assumes that paragraphs are indicated by two consecutive newlines ('\n\n').

txt = """
Poetry is a form of literature that uses aesthetic and rhythmic qualities of language—such as phonaesthetics, sound symbolism, and metre—to evoke meanings in addition to, or in place of, the prosaic ostensible meaning.

Poetry has a very long history, dating back to prehistorical times with the creation of hunting poetry in Africa, and panegyric and elegiac court poetry was developed extensively throughout the history of the empires of the Nile, Niger and Volta river valleys.
"""


def format_paragraph(paragraph, length, left, right):
    """Format paragraph ``p`` so the line length is at most ``length``
       with ``left`` as the number of characters for the left margin,
       and similiarly for ``right``.
    """
    words = paragraph.split()
    lines = []
    curline = ' ' * (left - 1)  # we add a space before the first word

    while words:
        word = words.pop(0)  # process the next word

        # +1 in the next line is for the space.
        if len(curline) + 1 + len(word) > length - right:
            # line would have been too long, start a new line
            lines.append(curline)
            curline = ' ' * (left - 1)
        curline += " " + word

    lines.append(curline)

    return '\n'.join(lines)


# we need to work on one paragraph at a time
paragraphs = txt.split('\n\n')

print('0123456789' * 8)  # print a ruler..

for paragraph in paragraphs:
    print(format_paragraph(paragraph, 80, left=4, right=5))
    print()  # next paragraph

the output of the above is:

01234567890123456789012345678901234567890123456789012345678901234567890123456789
    Poetry is a form of literature that uses aesthetic and rhythmic
    qualities of language such as phonaesthetics, sound symbolism, and
    metre to evoke meanings in addition to, or in place of, the prosaic
    ostensible meaning.

    Poetry has a very long history, dating back to prehistorical times with
    the creation of hunting poetry in Africa, and panegyric and elegiac
    court poetry was developed extensively throughout the history of the
    empires of the Nile, Niger and Volta river valleys.