Word Document Manipulation with python-docx

Critical: Split Placeholder Problem

The #1 issue with Word templates: Word often splits placeholder text across multiple XML runs. For example,

{{CANDIDATE_NAME}}

might be stored as:

• Run 1:

  {{CANDI

• Run 2:

  DATE_NAME}}

This happens due to spell-check, formatting changes, or Word's internal XML structure.

Naive Approach (FAILS on split placeholders)

# DON'T DO THIS - won't find split placeholders
for para in doc.paragraphs:
    for run in para.runs:
        if '{{NAME}}' in run.text:  # Won't match if split!
            run.text = run.text.replace('{{NAME}}', value)

Correct Approach: Paragraph-Level Search and Rebuild

import re

def replace_placeholder_robust(paragraph, placeholder, value):
    """Replace placeholder that may be split across runs."""
    full_text = paragraph.text
    if placeholder not in full_text:
        return False

    # Find all runs and their positions
    runs = paragraph.runs
    if not runs:
        return False

    # Build mapping of character positions to runs
    char_to_run = []
    for run in runs:
        for char in run.text:
            char_to_run.append(run)

    # Find placeholder position
    start_idx = full_text.find(placeholder)
    end_idx = start_idx + len(placeholder)

    # Get runs that contain the placeholder
    if start_idx >= len(char_to_run):
        return False

    start_run = char_to_run[start_idx]

    # Clear all runs and rebuild with replacement
    new_text = full_text.replace(placeholder, str(value))

    # Preserve first run's formatting, clear others
    for i, run in enumerate(runs):
        if i == 0:
            run.text = new_text
        else:
            run.text = ''

    return True

Best Practice: Regex-Based Full Replacement

import re
from docx import Document

def replace_all_placeholders(doc, data):
    """Replace all {{KEY}} placeholders with values from data dict."""

    def replace_in_paragraph(para):
        """Replace placeholders in a single paragraph."""
        text = para.text
        # Find all placeholders
        pattern = r'\{\{([A-Z_]+)\}\}'
        matches = re.findall(pattern, text)

        if not matches:
            return

        # Build new text with replacements
        new_text = text
        for key in matches:
            placeholder = '{{' + key + '}}'
            if key in data:
                new_text = new_text.replace(placeholder, str(data[key]))

        # If text changed, rebuild paragraph
        if new_text != text:
            # Clear all runs, put new text in first run
            runs = para.runs
            if runs:
                runs[0].text = new_text
                for run in runs[1:]:
                    run.text = ''

    # Process all paragraphs
    for para in doc.paragraphs:
        replace_in_paragraph(para)

    # Process tables (including nested)
    for table in doc.tables:
        for row in table.rows:
            for cell in row.cells:
                for para in cell.paragraphs:
                    replace_in_paragraph(para)
                # Handle nested tables
                for nested_table in cell.tables:
                    for nested_row in nested_table.rows:
                        for nested_cell in nested_row.cells:
                            for para in nested_cell.paragraphs:
                                replace_in_paragraph(para)

    # Process headers and footers
    for section in doc.sections:
        for para in section.header.paragraphs:
            replace_in_paragraph(para)
        for para in section.footer.paragraphs:
            replace_in_paragraph(para)

Headers and Footers

Headers/footers are separate from main document body:

from docx import Document

doc = Document('template.docx')

# Access headers/footers through sections
for section in doc.sections:
    # Header
    header = section.header
    for para in header.paragraphs:
        # Process paragraphs
        pass

    # Footer
    footer = section.footer
    for para in footer.paragraphs:
        # Process paragraphs
        pass

Nested Tables

Tables can contain other tables. Must recurse:

def process_table(table, data):
    """Process table including nested tables."""
    for row in table.rows:
        for cell in row.cells:
            # Process paragraphs in cell
            for para in cell.paragraphs:
                replace_in_paragraph(para, data)

            # Recurse into nested tables
            for nested_table in cell.tables:
                process_table(nested_table, data)

Conditional Sections

For

{{IF_CONDITION}}...{{END_IF_CONDITION}}

patterns:

def handle_conditional(doc, condition_key, should_include, data):
    """Remove or keep conditional sections."""
    start_marker = '{{IF_' + condition_key + '}}'
    end_marker = '{{END_IF_' + condition_key + '}}'

    for para in doc.paragraphs:
        text = para.text
        if start_marker in text and end_marker in text:
            if should_include:
                # Remove just the markers
                new_text = text.replace(start_marker, '').replace(end_marker, '')
                # Also replace any placeholders inside
                for key, val in data.items():
                    new_text = new_text.replace('{{' + key + '}}', str(val))
            else:
                # Remove entire content between markers
                new_text = ''

            # Apply to first run
            if para.runs:
                para.runs[0].text = new_text
                for run in para.runs[1:]:
                    run.text = ''

Complete Solution Pattern

from docx import Document
import json
import re

def fill_template(template_path, data_path, output_path):
    """Fill Word template handling all edge cases."""

    # Load data
    with open(data_path) as f:
        data = json.load(f)

    # Load template
    doc = Document(template_path)

    def replace_in_para(para):
        text = para.text
        pattern = r'\{\{([A-Z_]+)\}\}'
        if not re.search(pattern, text):
            return

        new_text = text
        for match in re.finditer(pattern, text):
            key = match.group(1)
            placeholder = match.group(0)
            if key in data:
                new_text = new_text.replace(placeholder, str(data[key]))

        if new_text != text and para.runs:
            para.runs[0].text = new_text
            for run in para.runs[1:]:
                run.text = ''

    # Main document
    for para in doc.paragraphs:
        replace_in_para(para)

    # Tables (with nesting)
    def process_table(table):
        for row in table.rows:
            for cell in row.cells:
                for para in cell.paragraphs:
                    replace_in_para(para)
                for nested in cell.tables:
                    process_table(nested)

    for table in doc.tables:
        process_table(table)

    # Headers/Footers
    for section in doc.sections:
        for para in section.header.paragraphs:
            replace_in_para(para)
        for para in section.footer.paragraphs:
            replace_in_para(para)

    doc.save(output_path)

# Usage
fill_template('template.docx', 'data.json', 'output.docx')

Common Pitfalls

1. Forgetting headers/footers - They're not in

   doc.paragraphs

2. Missing nested tables - Must recurse into

   cell.tables

3. Split placeholders - Always work at paragraph level, not run level
4. Losing formatting - Keep first run's formatting when rebuilding
5. Conditional markers left behind - Remove

   {{IF_...}}

   markers after processing